ts-11-mini-sql
0.000
Challenge · difficulty 5/5
# In-memory SQL SELECT engine
Implement a file **`solution.ts`** that parses a small `SELECT` statement and executes
it against an in-memory table of rows. This is a parser + interpreter exercise: you must
tokenize the query, build a small AST, validate it, and evaluate it over the data.
## Types to export
```ts
export type Row = Record<string, number | string>;
export class QueryError extends Error {}
// Parse and execute a small SQL SELECT against the given rows. Returns the result rows.
export function query(sql: string, rows: Row[]): Row[];
```
The `rows` argument **is** the table; the table name in the query is accepted but
otherwise ignored (the data comes from `rows` regardless of the name written).
## Grammar
```
SELECT <cols> FROM <table> [WHERE <cond>] [ORDER BY <col> [ASC|DESC]] [LIMIT <n>]
```
The clauses, when present, must appear in exactly this order. The four optional clauses
(`WHERE`, `ORDER BY`, `LIMIT`) are each optional and independent.
### `<cols>`
- `*` selects **all** columns. Each result row preserves that source row's own key
insertion order (rows are copied; no column is renamed or reordered).
- Otherwise a comma-separated list of column names, e.g. `name, age`. The result rows
then contain **exactly** those columns, **in the listed order**. A selected column that
is missing from a given source row is simply omitted from that row's output (it is not
an error, and no placeholder value is inserted).
### `<table>`
A bare identifier (letters, digits, `_`, not starting with a digit). Any name is accepted.
### `<cond>` (the `WHERE` clause)
One or more comparisons combined with `AND` / `OR`. There are **no parentheses**.
`AND` binds **tighter** than `OR`, so
```
a = 1 AND b = 2 OR c = 3
```
parses as `(a = 1 AND b = 2) OR (c = 3)`.
A single comparison is `col <op> value` where:
- `<op>` is one of `= != < > <= >=`.
- `value` is either an **integer literal** (optionally signed, e.g. `42`, `-3`, `0`) or a
**single-quoted string** (e.g. `'alice'`). Strings may contain spaces; an unterminated
string literal is an error.
Comparison semantics, given `cell = row[col]`:
- `=` / `!=` work for both numbers and strings using strict (in)equality. If `cell` is a
number and `value` is a string (or vice versa), they are considered **not equal** (so
`=` is `false`, `!=` is `true`).
- `< > <= >=` are ordering comparisons:
- both number -> numeric comparison;
- both string -> lexicographic comparison (JavaScript `<`/`>` on strings);
- **type mismatch** (one number, one string) -> the comparison is **`false`**.
- If `col` is **not present** in the row, the comparison is treated as a non-match:
`=` is `false`, `!=` is `true`, and every ordering comparison is `false`. This does
**not** throw — only *syntactically* invalid queries throw.
A row is included iff the whole `<cond>` evaluates to true for it. With no `WHERE`, all
rows match.
### `ORDER BY <col> [ASC|DESC]`
Sort the result by a single column. `ASC` (the default) sorts ascending; `DESC`
descending. Numbers sort numerically, strings lexicographically. The sort must be
**stable**: rows that compare equal keep their relative input order. A mismatched-type or
missing sort key compares as equal to the others (it does not throw and does not crash);
ties are broken by stability (original order).
### `LIMIT <n>`
Keep the first `n` result rows after ordering. `n` must be a **non-negative integer**.
### Case sensitivity
Keywords (`SELECT`, `FROM`, `WHERE`, `AND`, `OR`, `ORDER`, `BY`, `ASC`, `DESC`, `LIMIT`)
are **case-insensitive** — `select` and `SELECT` are equivalent. Column names and quoted
string values are **case-sensitive**.
## Evaluation order
`WHERE` filtering -> `ORDER BY` sorting -> `LIMIT` truncation -> column projection.
(Projection last means you may order by a column you did not select.)
## Errors — throw `QueryError`
Throw a `QueryError` (not a plain `Error`) for any **syntactically invalid** query,
including:
- a statement that does not start with `SELECT`, or has no `FROM`;
- an empty column list, or a trailing/embedded comma in the column list;
- an unknown clause / leftover tokens after a valid statement;
- a bad comparison operator, or a comparison missing its column / operator / value;
- an unterminated single-quoted string;
- a `LIMIT` whose argument is missing or is not a non-negative integer;
- an `ORDER BY` without a column.
Referencing a column that is absent from a particular row at **evaluation** time (in
`WHERE` or `ORDER BY`) is **not** an error — see the semantics above.
## Worked example
```ts
const rows: Row[] = [
{ id: 1, name: "alice", age: 30 },
{ id: 2, name: "bob", age: 25 },
{ id: 3, name: "carol", age: 30 },
{ id: 4, name: "dave", age: 17 },
];
query(
"SELECT name, age FROM users WHERE age >= 18 ORDER BY age DESC LIMIT 2",
rows,
);
// WHERE drops dave (17). Remaining: alice(30), bob(25), carol(30).
// ORDER BY age DESC (stable): alice(30), carol(30), bob(25).
// LIMIT 2: alice(30), carol(30).
// Projection name, age:
// -> [ { name: "alice", age: 30 }, { name: "carol", age: 30 } ]
```
Keep it fully typed: `solution.ts` must pass `tsc --noEmit` in strict mode. Do not use
`any` in the implementation; prefer `unknown` and narrow.
tests/solution.test.ts
import { test } from "node:test";
import { strict as assert } from "node:assert";
import { query, QueryError, type Row } from "./solution.ts";
function people(): Row[] {
return [
{ id: 1, name: "alice", age: 30, city: "NYC" },
{ id: 2, name: "bob", age: 25, city: "LA" },
{ id: 3, name: "carol", age: 30, city: "NYC" },
{ id: 4, name: "dave", age: 17, city: "SF" },
];
}
test("SELECT * preserves all columns and per-row key order", () => {
const rows: Row[] = [{ z: 1, a: "x", m: 2 }];
const out = query("SELECT * FROM t", rows);
assert.deepEqual(out, [{ z: 1, a: "x", m: 2 }]);
assert.deepEqual(Object.keys(out[0]!), ["z", "a", "m"]);
// Result is a copy, not the same object.
assert.notEqual(out[0], rows[0]);
});
test("explicit column list selects exactly those columns in order", () => {
const out = query("SELECT name, id FROM users", people());
assert.deepEqual(out, [
{ name: "alice", id: 1 },
{ name: "bob", id: 2 },
{ name: "carol", id: 3 },
{ name: "dave", id: 4 },
]);
assert.deepEqual(Object.keys(out[0]!), ["name", "id"]);
});
test("selected column missing from a row is omitted, not an error", () => {
const rows: Row[] = [{ a: 1, b: 2 }, { a: 3 }];
const out = query("SELECT a, b FROM t", rows);
assert.deepEqual(out, [{ a: 1, b: 2 }, { a: 3 }]);
});
test("WHERE = and != on numbers", () => {
assert.deepEqual(
query("SELECT name FROM u WHERE age = 30", people()),
[{ name: "alice" }, { name: "carol" }],
);
assert.deepEqual(
query("SELECT name FROM u WHERE age != 30", people()),
[{ name: "bob" }, { name: "dave" }],
);
});
test("WHERE = and != on strings (case-sensitive values)", () => {
assert.deepEqual(
query("SELECT name FROM u WHERE city = 'NYC'", people()),
[{ name: "alice" }, { name: "carol" }],
);
// Wrong case does not match.
assert.deepEqual(query("SELECT name FROM u WHERE city = 'nyc'", people()), []);
assert.deepEqual(
query("SELECT name FROM u WHERE name != 'alice'", people()).length,
3,
);
});
test("numeric ordering comparisons < > <= >=", () => {
assert.deepEqual(
query("SELECT name FROM u WHERE age < 30", people()),
[{ name: "bob" }, { name: "dave" }],
);
assert.deepEqual(
query("SELECT name FROM u WHERE age > 25", people()),
[{ name: "alice" }, { name: "carol" }],
);
assert.deepEqual(
query("SELECT name FROM u WHERE age <= 25", people()),
[{ name: "bob" }, { name: "dave" }],
);
assert.deepEqual(
query("SELECT name FROM u WHERE age >= 30", people()),
[{ name: "alice" }, { name: "carol" }],
);
});
test("lexicographic string ordering comparisons", () => {
assert.deepEqual(
query("SELECT name FROM u WHERE name < 'carol'", people()),
[{ name: "alice" }, { name: "bob" }],
);
assert.deepEqual(
query("SELECT name FROM u WHERE name >= 'carol'", people()),
[{ name: "carol" }, { name: "dave" }],
);
});
test("negative integer literals", () => {
const rows: Row[] = [{ t: -5 }, { t: 0 }, { t: 3 }];
assert.deepEqual(query("SELECT t FROM r WHERE t < 0", rows), [{ t: -5 }]);
assert.deepEqual(query("SELECT t FROM r WHERE t = -5", rows), [{ t: -5 }]);
assert.deepEqual(query("SELECT t FROM r WHERE t >= -5", rows), [
{ t: -5 },
{ t: 0 },
{ t: 3 },
]);
});
test("AND binds tighter than OR", () => {
const rows: Row[] = [
{ a: 1, b: 2, c: 9 }, // a=1 AND b=2 -> true
{ a: 1, b: 5, c: 3 }, // c=3 -> true via OR
{ a: 9, b: 9, c: 9 }, // none -> false
];
// (a = 1 AND b = 2) OR (c = 3)
const out = query("SELECT a FROM t WHERE a = 1 AND b = 2 OR c = 3", rows);
assert.deepEqual(out, [{ a: 1 }, { a: 1 }]);
});
test("OR then AND precedence: a = 1 OR a = 2 AND b = 9", () => {
const rows: Row[] = [
{ a: 1, b: 0 }, // a=1 -> true
{ a: 2, b: 9 }, // a=2 AND b=9 -> true
{ a: 2, b: 0 }, // a=2 but b!=9 -> false
];
// parses as a = 1 OR (a = 2 AND b = 9)
const out = query("SELECT a, b FROM t WHERE a = 1 OR a = 2 AND b = 9", rows);
assert.deepEqual(out, [{ a: 1, b: 0 }, { a: 2, b: 9 }]);
});
test("ORDER BY ascending (default) and DESC", () => {
const asc = query("SELECT name FROM u ORDER BY age", people());
assert.deepEqual(asc.map((r) => r["name"]), ["dave", "bob", "alice", "carol"]);
const desc = query("SELECT name FROM u ORDER BY age DESC", people());
assert.deepEqual(desc.map((r) => r["name"]), ["alice", "carol", "bob", "dave"]);
});
test("ORDER BY is stable for equal keys", () => {
// alice and carol both have age 30; original order alice before carol.
const asc = query("SELECT name FROM u ORDER BY age ASC", people());
const names = asc.map((r) => r["name"]);
assert.ok(names.indexOf("alice") < names.indexOf("carol"));
const desc = query("SELECT name FROM u ORDER BY age DESC", people());
const dnames = desc.map((r) => r["name"]);
// Stability preserved under DESC too: equal keys keep input order.
assert.ok(dnames.indexOf("alice") < dnames.indexOf("carol"));
});
test("ORDER BY a column not in the SELECT list, plus LIMIT", () => {
const out = query(
"SELECT name FROM u WHERE age >= 18 ORDER BY age DESC LIMIT 2",
people(),
);
assert.deepEqual(out, [{ name: "alice" }, { name: "carol" }]);
});
test("LIMIT keeps first n and LIMIT 0 yields empty", () => {
assert.deepEqual(
query("SELECT id FROM u ORDER BY id LIMIT 2", people()),
[{ id: 1 }, { id: 2 }],
);
assert.deepEqual(query("SELECT id FROM u LIMIT 0", people()), []);
// LIMIT larger than result is fine.
assert.deepEqual(query("SELECT id FROM u ORDER BY id LIMIT 99", people()).length, 4);
});
test("type-mismatch comparisons: = is false, != is true, ordering is false", () => {
const rows: Row[] = [{ v: 5 }, { v: "5" }];
// number cell vs string literal
assert.deepEqual(query("SELECT v FROM t WHERE v = '5'", rows), [{ v: "5" }]);
assert.deepEqual(query("SELECT v FROM t WHERE v != '5'", rows), [{ v: 5 }]);
// ordering of number cell vs string literal is a type mismatch -> false,
// but the string cell "5" vs string literal '9' is a valid string comparison.
assert.deepEqual(query("SELECT v FROM t WHERE v < '9'", rows), [{ v: "5" }]);
// numeric cell 5 vs string '9' is a mismatch (false); string cell "5" vs number 0 too.
assert.deepEqual(query("SELECT v FROM t WHERE v > 0", rows), [{ v: 5 }]);
});
test("missing column in WHERE: = false, != true, ordering false (no throw)", () => {
const rows: Row[] = [{ a: 1 }, { a: 2 }];
assert.deepEqual(query("SELECT a FROM t WHERE missing = 1", rows), []);
assert.deepEqual(query("SELECT a FROM t WHERE missing != 1", rows), [{ a: 1 }, { a: 2 }]);
assert.deepEqual(query("SELECT a FROM t WHERE missing > 0", rows), []);
});
test("ORDER BY with missing / mismatched keys does not throw", () => {
const rows: Row[] = [{ a: 2 }, { b: 1 }, { a: 1 }];
// Rows without `a` compare as equal; should not throw.
const out = query("SELECT * FROM t ORDER BY a", rows);
assert.equal(out.length, 3);
});
test("keywords are case-insensitive; identifiers/strings are not", () => {
const out = query(
"select Name from u WHERE City = 'NYC' order by Age desc limit 1",
people().map((r) => ({ Name: String(r["name"]), City: String(r["city"]), Age: Number(r["age"]) })),
);
assert.deepEqual(out, [{ Name: "alice" }]);
// Mixed-case keywords work too.
assert.deepEqual(
query("SeLeCt id FrOm u Where age = 25", people()),
[{ id: 2 }],
);
});
test("no WHERE returns all rows; whitespace is tolerated", () => {
assert.equal(query(" SELECT * FROM t ", people()).length, 4);
});
test("throws: missing SELECT", () => {
assert.throws(() => query("FROM t", []), QueryError);
});
test("throws: missing FROM", () => {
assert.throws(() => query("SELECT *", []), QueryError);
assert.throws(() => query("SELECT a, b", []), QueryError);
});
test("throws: empty / malformed column list", () => {
assert.throws(() => query("SELECT FROM t", []), QueryError);
assert.throws(() => query("SELECT a, FROM t", []), QueryError);
assert.throws(() => query("SELECT , a FROM t", []), QueryError);
});
test("throws: bad operator and malformed comparison", () => {
assert.throws(() => query("SELECT * FROM t WHERE a == 1", []), QueryError);
assert.throws(() => query("SELECT * FROM t WHERE a 1", []), QueryError);
assert.throws(() => query("SELECT * FROM t WHERE a =", []), QueryError);
assert.throws(() => query("SELECT * FROM t WHERE = 1", []), QueryError);
});
test("throws: unterminated string literal", () => {
assert.throws(() => query("SELECT * FROM t WHERE name = 'alice", []), QueryError);
});
test("throws: bad LIMIT (missing, negative, non-integer, string)", () => {
assert.throws(() => query("SELECT * FROM t LIMIT", []), QueryError);
assert.throws(() => query("SELECT * FROM t LIMIT -1", []), QueryError);
assert.throws(() => query("SELECT * FROM t LIMIT 'x'", []), QueryError);
});
test("throws: unknown clause / leftover tokens", () => {
assert.throws(() => query("SELECT * FROM t GROUP BY a", []), QueryError);
assert.throws(() => query("SELECT * FROM t WHERE a = 1 b = 2", []), QueryError);
assert.throws(() => query("SELECT * FROM t ORDER BY", []), QueryError);
});
System prompt
You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.Errors (stderr)
no code extracted from responseReasoning (chain-of-thought)
Let me break down this problem:
1. I need to implement a SQL SELECT parser and interpreter in TypeScript
2. The grammar is: `SELECT <cols> FROM <table> [WHERE <cond>] [ORDER BY <col> [ASC|DESC]] [LIMIT <n>]`
3. I need to tokenize, parse into AST, validate, and evaluate
Let me think through the components:
### Tokenizer
- Keywords: SELECT, FROM, WHERE, AND, OR, ORDER, BY, ASC, DESC, LIMIT (case-insensitive)
- Identifiers: letters, digits, _, not starting with digit
- Operators: =, !=, <, >, <=, >=
- Literals: integers (optionally signed), single-quoted strings
- Punctuation: *, comma, parentheses (not used in grammar but might appear)
### Parser
- Parse SELECT <cols> FROM <table>
- Optionally parse WHERE <cond>
- Optionally parse ORDER BY <col> [ASC|DESC]
- Optionally parse LIMIT <n>
- Ensure no leftover tokens
### AST
- Columns: `*` or list of column names
- Table name
- WHERE condition: tree of AND/OR with leaf comparisons
- ORDER BY: column name + direction
- LIMIT: number
### Evaluation
1. WHERE filtering
2. ORDER BY sorting
3. LIMIT truncation
4. Column projection
Let me think about the WHERE condition parsing more carefully:
- AND binds tighter than OR
- No parentheses
- So I need to parse OR as the top level, and AND as the next level
For the condition:
```
cond := or_expr
or_expr := and_expr (OR and_expr)*
and_expr := comparison (AND comparison)*
comparison := col op value
```
Let me think about tokenization more carefully:
- I need to handle whitespace
- I need to handle single-quoted strings (which can contain spaces)
- I need to handle operators like <=, >=, != which are two characters
Let me think about the signed integer issue. The grammar says "optionally signed, e.g. 42, -3, 0". But `-` could also be a unary minus in front of a number. However, in the context of a comparison value, `-3` should be parsed as a single integer token. But wait, what about `col < -3`? The `-` here is part of the value, not an operator.
Actually, let me reconsider. The token `-3` should be recognized as a single integer token. But how do I distinguish between `-` as part of a negative number and `-` as something else? In SQL, `-3` is a single token. Let me handle this in the tokenizer: when I see a `-` followed by a digit, I treat it as part of the number.
Wait, but what about `col - 3`? That's not a valid operator in our grammar. The operators are `=`, `!=`, `<`, `>`, `<=`, `>=`. So `-` by itself is not an operator. So `-3` can safely be treated as a single integer token.
Actually, let me reconsider. What if someone writes `col < -3`? The tokenizer would see `<` as an operator and `-3` as a number. That works.
But what about `col != -3`? The tokenizer would see `!=` as an operator and `-3` as a number. That works too.
What about `col > -3`? The tokenizer would see `>` as an operator and `-3` as a number. That works.
OK so the tokenizer needs to handle:
1. Whitespace (skip)
2. Single-quoted strings
3. Operators: <=, >=, !=, =, <, >
4. Numbers: optional `-` followed by digits
5. Identifiers/keywords: letters, digits, _, not starting with digit
6. Punctuation: *, comma
Wait, I need to be careful about the `-` sign. If I see `-3`, I should tokenize it as a number. But what if I see `-` followed by a space and then `3`? That would be `-` (not a valid operator) followed by `3`. But `-` is not a valid operator in our grammar, so this would be a syntax error.
Actually, let me think again. The `-` sign is only valid as part of a number literal. So in the tokenizer, when I see `-` followed immediately by a digit, I consume it as part of the number. If I see `-` not followed by a digit, it's... well, it's not a valid token in our grammar. Let me just treat it as an error.
Hmm, but actually, what about `col < -3`? The `<` is an operator, and `-3` is a number. The tokenizer would see `<` and then `-3`. That's fine.
But what about `col < - 3`? The `<` is an operator, and then `-` is... not a valid token. This would be a syntax error. That seems correct.
Let me now think about the tokenizer implementation:
```typescript
type Token =
| { type: 'keyword'; value: string }
| { type: 'identifier'; value: string }
| { type: 'number'; value: number }
| { type: 'string'; value: string }
| { type: 'operator'; value: string }
| { type: 'star' }
| { type: 'comma' }
| { type: 'eof' };
```
Actually, let me simplify. Keywords and identifiers can be distinguished by checking against a keyword set. So I can have:
```typescript
type TokenType = 'IDENT' | 'NUMBER' | 'STRING' | 'OP' | 'STAR' | 'COMMA' | 'EOF';
interface Token {
type: TokenType;
value: string;
}
```
For keywords, I'll check the IDENT value against a set of known keywords.
Let me now think about the parser:
```typescript
interface SelectStmt {
columns: '*' | string[];
table: string;
where?: Condition;
orderBy?: { column: string; direction: 'ASC' | 'DESC' };
limit?: number;
}
interface Condition {
type: 'AND' | 'OR';
left: Condition | Comparison;
right: Condition | Comparison;
}
interface Comparison {
column: string;
operator: '=' | '!=' | '<' | '>' | '<=' | '>=';
value: number | string;
}
```
Actually, let me think about the condition structure more carefully. Since AND binds tighter than OR, I can represent it as:
```typescript
type Condition =
| { type: 'OR'; left: Condition; right: Condition }
| { type: 'AND'; left: Condition; right: Condition }
| { type: 'comparison'; column: string; operator: string; value: number | string };
```
Wait, but this doesn't quite work because AND and OR are binary operators. Let me think again.
Actually, the simplest approach is:
- `or_expr` = `and_expr` (`OR` `and_expr`)*
- `and_expr` = `comparison` (`AND` `comparison`)*
So I can represent it as a tree where OR nodes have AND nodes as children, and AND nodes have comparison nodes as children.
Let me simplify and just use a flat representation:
```typescript
type Condition =
| { type: 'OR'; left: Condition; right: Condition }
| { type: 'AND'; left: Condition; right: Condition }
| { type: 'comparison'; column: string; operator: str
…[20504 chars elided]…
see:
- `=` as... not an IDENT. So `consumeIdent` would throw an error. That's correct.
Now let me think about the ORDER BY error handling:
- "an ORDER BY without a column" -> throw QueryError
So if someone writes `ORDER BY`, the parser would see:
- `ORDER` keyword
- `BY` keyword
- EOF (not an IDENT). So `consumeIdent` would throw an error. That's correct.
Now let me think about the LIMIT error handling:
- "a LIMIT whose argument is missing or is not a non-negative integer" -> throw QueryError
So if someone writes `LIMIT`, the parser would see:
- `LIMIT` keyword
- EOF (not a NUMBER). So it would throw an error. That's correct.
What about `LIMIT -1`? The parser would see:
- `LIMIT` keyword
- `-1` as a NUMBER token with value `-1`
- `parseInt('-1', 10)` returns `-1`, which is negative. So it would throw an error. That's correct.
Wait, but what about `LIMIT 0`? That should be valid (returns no rows). Let me check: `parseInt('0', 10)` returns `0`, which is non-negative. So it's valid. That's correct.
What about `LIMIT 1.5`? The tokenizer would see `1` as a NUMBER and `.5` as... well, `.` is not a valid character. So it would throw an error. That's correct.
Actually wait, let me reconsider. The tokenizer would see `1` as a NUMBER, then `.` as an unexpected character. So it would throw an error. That's correct.
Now let me think about the column list validation more carefully. The spec says:
- "an empty column list, or a trailing/embedded comma in the column list"
So `SELECT , FROM table` is an error (empty column list with leading comma).
`SELECT a, FROM table` is an error (trailing comma).
`SELECT a,,b FROM table` is an error (embedded comma).
My parser handles these cases:
- `SELECT , FROM table`: The parser sees `,` after `SELECT`, which is not a STAR or IDENT. So it would throw an error for empty column list. Wait, let me check my code...
Actually, in my code, I check:
```typescript
if (peek().type === 'STAR') {
consume();
columns = '*';
} else if (peek().type === 'COMMA') {
throw new QueryError('Self-repair attempts
[
{
"total": 1,
"answer": "",
"passed": 0,
"reasoning": "Let me break down this problem:\n\n1. I need to implement a SQL SELECT parser and interpreter in TypeScript\n2. The grammar is: `SELECT <cols> FROM <table> [WHERE <cond>] [ORDER BY <col> [ASC|DESC]] [LIMIT <n>]`\n3. I need to tokenize, parse into AST, validate, and evaluate\n\nLet me think through the components:\n\n### Tokenizer\n- Keywords: SELECT, FROM, WHERE, AND, OR, ORDER, BY, ASC, DESC, LIMIT (case-insensitive)\n- Identifiers: letters, digits, _, not starting with digit\n- Operators: =, !=, <, >, <=, >=\n- Literals: integers (optionally signed), single-quoted strings\n- Punctuation: *, comma, parentheses (not used in grammar but might appear)\n\n### Parser\n- Parse SELECT <cols> FROM <table>\n- Optionally parse WHERE <cond>\n- Optionally parse ORDER BY <col> [ASC|DESC]\n- Optionally parse LIMIT <n>\n- Ensure no leftover tokens\n\n### AST\n- Columns: `*` or list of column names\n- Table name\n- WHERE condition: tree of AND/OR with leaf comparisons\n- ORDER BY: column name + direction\n- LIMIT: number\n\n### Evaluation\n1. WHERE filtering\n2. ORDER BY sorting\n3. LIMIT truncation\n4. Column projection\n\nLet me think about the WHERE condition parsing more carefully:\n- AND binds tighter than OR\n- No parentheses\n- So I need to parse OR as the top level, and AND as the next level\n\nFor the condition:\n```\ncond := or_expr\nor_expr := and_expr (OR and_expr)*\nand_expr := comparison (AND comparison)*\ncomparison := col op value\n```\n\nLet me think about tokenization more carefully:\n- I need to handle whitespace\n- I need to handle single-quoted strings (which can contain spaces)\n- I need to handle operators like <=, >=, != which are two characters\n\nLet me think about the signed integer issue. The grammar says \"optionally signed, e.g. 42, -3, 0\". But `-` could also be a unary minus in front of a number. However, in the context of a comparison value, `-3` should be parsed as a single integer token. But wait, what about `col < -3`? The `-` here is part of the value, not an operator.\n\nActually, let me reconsider. The token `-3` should be recognized as a single integer token. But how do I distinguish between `-` as part of a negative number and `-` as something else? In SQL, `-3` is a single token. Let me handle this in the tokenizer: when I see a `-` followed by a digit, I treat it as part of the number.\n\nWait, but what about `col - 3`? That's not a valid operator in our grammar. The operators are `=`, `!=`, `<`, `>`, `<=`, `>=`. So `-` by itself is not an operator. So `-3` can safely be treated as a single integer token.\n\nActually, let me reconsider. What if someone writes `col < -3`? The tokenizer would see `<` as an operator and `-3` as a number. That works.\n\nBut what about `col != -3`? The tokenizer would see `!=` as an operator and `-3` as a number. That works too.\n\nWhat about `col > -3`? The tokenizer would see `>` as an operator and `-3` as a number. That works.\n\nOK so the tokenizer needs to handle:\n1. Whitespace (skip)\n2. Single-quoted strings\n3. Operators: <=, >=, !=, =, <, >\n4. Numbers: optional `-` followed by digits\n5. Identifiers/keywords: letters, digits, _, not starting with digit\n6. Punctuation: *, comma\n\nWait, I need to be careful about the `-` sign. If I see `-3`, I should tokenize it as a number. But what if I see `-` followed by a space and then `3`? That would be `-` (not a valid operator) followed by `3`. But `-` is not a valid operator in our grammar, so this would be a syntax error.\n\nActually, let me think again. The `-` sign is only valid as part of a number literal. So in the tokenizer, when I see `-` followed immediately by a digit, I consume it as part of the number. If I see `-` not followed by a digit, it's... well, it's not a valid token in our grammar. Let me just treat it as an error.\n\nHmm, but actually, what about `col < -3`? The `<` is an operator, and `-3` is a number. The tokenizer would see `<` and then `-3`. That's fine.\n\nBut what about `col < - 3`? The `<` is an operator, and then `-` is... not a valid token. This would be a syntax error. That seems correct.\n\nLet me now think about the tokenizer implementation:\n\n```typescript\ntype Token = \n | { type: 'keyword'; value: string }\n | { type: 'identifier'; value: string }\n | { type: 'number'; value: number }\n | { type: 'string'; value: string }\n | { type: 'operator'; value: string }\n | { type: 'star' }\n | { type: 'comma' }\n | { type: 'eof' };\n```\n\nActually, let me simplify. Keywords and identifiers can be distinguished by checking against a keyword set. So I can have:\n\n```typescript\ntype TokenType = 'IDENT' | 'NUMBER' | 'STRING' | 'OP' | 'STAR' | 'COMMA' | 'EOF';\n\ninterface Token {\n type: TokenType;\n value: string;\n}\n```\n\nFor keywords, I'll check the IDENT value against a set of known keywords.\n\nLet me now think about the parser:\n\n```typescript\ninterface SelectStmt {\n columns: '*' | string[];\n table: string;\n where?: Condition;\n orderBy?: { column: string; direction: 'ASC' | 'DESC' };\n limit?: number;\n}\n\ninterface Condition {\n type: 'AND' | 'OR';\n left: Condition | Comparison;\n right: Condition | Comparison;\n}\n\ninterface Comparison {\n column: string;\n operator: '=' | '!=' | '<' | '>' | '<=' | '>=';\n value: number | string;\n}\n```\n\nActually, let me think about the condition structure more carefully. Since AND binds tighter than OR, I can represent it as:\n\n```typescript\ntype Condition = \n | { type: 'OR'; left: Condition; right: Condition }\n | { type: 'AND'; left: Condition; right: Condition }\n | { type: 'comparison'; column: string; operator: string; value: number | string };\n```\n\nWait, but this doesn't quite work because AND and OR are binary operators. Let me think again.\n\nActually, the simplest approach is:\n- `or_expr` = `and_expr` (`OR` `and_expr`)*\n- `and_expr` = `comparison` (`AND` `comparison`)*\n\nSo I can represent it as a tree where OR nodes have AND nodes as children, and AND nodes have comparison nodes as children.\n\nLet me simplify and just use a flat representation:\n\n```typescript\ntype Condition = \n | { type: 'OR'; left: Condition; right: Condition }\n | { type: 'AND'; left: Condition; right: Condition }\n | { type: 'comparison'; column: string; operator: str\n…[20504 chars elided]…\n see:\n- `=` as... not an IDENT. So `consumeIdent` would throw an error. That's correct.\n\nNow let me think about the ORDER BY error handling:\n- \"an ORDER BY without a column\" -> throw QueryError\n\nSo if someone writes `ORDER BY`, the parser would see:\n- `ORDER` keyword\n- `BY` keyword\n- EOF (not an IDENT). So `consumeIdent` would throw an error. That's correct.\n\nNow let me think about the LIMIT error handling:\n- \"a LIMIT whose argument is missing or is not a non-negative integer\" -> throw QueryError\n\nSo if someone writes `LIMIT`, the parser would see:\n- `LIMIT` keyword\n- EOF (not a NUMBER). So it would throw an error. That's correct.\n\nWhat about `LIMIT -1`? The parser would see:\n- `LIMIT` keyword\n- `-1` as a NUMBER token with value `-1`\n- `parseInt('-1', 10)` returns `-1`, which is negative. So it would throw an error. That's correct.\n\nWait, but what about `LIMIT 0`? That should be valid (returns no rows). Let me check: `parseInt('0', 10)` returns `0`, which is non-negative. So it's valid. That's correct.\n\nWhat about `LIMIT 1.5`? The tokenizer would see `1` as a NUMBER and `.5` as... well, `.` is not a valid character. So it would throw an error. That's correct.\n\nActually wait, let me reconsider. The tokenizer would see `1` as a NUMBER, then `.` as an unexpected character. So it would throw an error. That's correct.\n\nNow let me think about the column list validation more carefully. The spec says:\n- \"an empty column list, or a trailing/embedded comma in the column list\"\n\nSo `SELECT , FROM table` is an error (empty column list with leading comma).\n`SELECT a, FROM table` is an error (trailing comma).\n`SELECT a,,b FROM table` is an error (embedded comma).\n\nMy parser handles these cases:\n- `SELECT , FROM table`: The parser sees `,` after `SELECT`, which is not a STAR or IDENT. So it would throw an error for empty column list. Wait, let me check my code...\n\nActually, in my code, I check:\n```typescript\nif (peek().type === 'STAR') {\n consume();\n columns = '*';\n} else if (peek().type === 'COMMA') {\n throw new QueryError('",
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"reasoning": "The user wants me to implement an in-memory SQL SELECT engine in TypeScript.\nI need to output a single file `solution.ts` with the exact types and function signatures requested.\n\nLet's break down the requirements:\n1. **Types**: `Row`, `QueryError`, `query(sql: string, rows: Row[]): Row[]`\n2. **Grammar**: `SELECT <cols> FROM <table> [WHERE <cond>] [ORDER BY <col> [ASC|DESC]] [LIMIT <n>]`\n3. **Tokenization**: Need to handle keywords (case-insensitive), identifiers, numbers, strings, operators, commas, asterisks.\n4. **Parsing**: Build an AST or directly parse into a structured representation.\n - Columns: `*` or list of identifiers.\n - Table: identifier.\n - Where: conditions combined with AND/OR. AND binds tighter than OR. No parentheses.\n - Order By: column, optional ASC/DESC.\n - Limit: non-negative integer.\n5. **Evaluation**:\n - Filter rows based on WHERE.\n - Sort based on ORDER BY.\n - Limit based on LIMIT.\n - Project columns.\n6. **Error Handling**: Throw `QueryError` for syntax errors.\n7. **Type Safety**: Strict TypeScript, no `any`.\n\nLet's design the tokenizer first.\nTokens:\n- `SELECT`, `FROM`, `WHERE`, `AND`, `OR`, `ORDER`, `BY`, `ASC`, `DESC`, `LIMIT` (Keywords)\n- `IDENT` (identifiers)\n- `NUMBER` (integers, optionally signed? The grammar says integer literal optionally signed in comparisons, but LIMIT must be non-negative. I'll tokenize numbers as sequences of digits, and handle `-` as a separate token or part of the number if it's a unary minus. Actually, it's easier to tokenize `-` as an operator/unary minus, or just handle signed numbers in the lexer if preceded by `=` or start of condition. Let's stick to standard SQL-ish: `-` is a token, but for simplicity in this constrained grammar, I'll treat `-` followed by digits as a negative number token if it appears where a value is expected, or just tokenize `-` separately and handle it in parsing. Actually, the prompt says \"optionally signed, e.g. 42, -3, 0\". I'll tokenize `-` as a separate token `MINUS` or just handle it in the parser. Let's tokenize numbers as `[0-9]+`. If I see `-` before a number in a value position, I'll combine them or handle in parser. Actually, it's safer to tokenize `-` as a separate token `OP` or `MINUS`, but the prompt says `<op>` is one of `= != < > <= >=`. So `-` is only for negative numbers. I'll make the lexer recognize `-?[0-9]+` as a number token when appropriate, or just always recognize `-` as a token and handle it. Let's keep it simple: lexer produces `NUMBER` for `[0-9]+`, and `-` is a separate token. In the parser, when expecting a value, if I see `-` followed by `NUMBER`, I'll combine them. Or I can just make the lexer recognize `-?[0-9]+` as `NUMBER`. That's easier.)\n- `STRING` (single-quoted)\n- `OP` (`=`, `!=`, `<`, `>`, `<=`, `>=`)\n- `COMMA`\n- `STAR` (`*`)\n- `EOF`\n\nLet's refine the lexer:\nKeywords are case-insensitive. I'll uppercase them for matching.\nIdentifiers: `[a-zA-Z_][a-zA-Z0-9_]*`\nNumbers: `-?[0-9]+` (but careful: `-` might be an operator in other contexts? The grammar only uses `-` for negative numbers in values. So `-?[0-9]+` is fine.)\nStrings: `'[^']*'` (unterminated is error)\nOperators: `<=`, `>=`, `!=`, `=`, `<`, `>`\nPunctuation: `,`, `*`\n\nWait, `-` could be ambiguous if we just do `-?[0-9]+`. But in this grammar, `-` only appears in values. So it's fine.\n\nLet's write a simple tokenizer class/function.\n\n```typescript\ntype TokenType = \n | 'SELECT' | 'FROM' | 'WHERE' | 'AND' | 'OR' | 'ORDER' | 'BY' | 'ASC' | 'DESC' | 'LIMIT'\n | 'IDENT' | 'NUMBER' | 'STRING' | 'OP' | 'COMMA' | 'STAR' | 'EOF';\n\ninterface Token {\n type: TokenType;\n value: string;\n}\n\nfunction tokenize(sql: string): Token[] {\n const tokens: Token[] = [];\n let i = 0;\n const len = sql.length;\n \n while (i < len) {\n if (/\\s/.test(sql[i])) { i++; continue; }\n \n if (/[a-zA-Z_]/.test(sql[i])) {\n let start = i;\n while (i < len && /[a-zA-Z0-9_]/.test(sql[i])) i++;\n const word = sql.slice(start, i);\n const upper = word.toUpperCase();\n if (['SELECT','FROM','WHERE','AND','OR','ORDER','BY','ASC','DESC','LIMIT'].includes(upper)) {\n tokens.push({ type: upper as TokenType, value: word });\n } else {\n tokens.push({ type: 'IDENT', value: word });\n }\n continue;\n }\n \n if (/[0-9]/.test(sql[i]) || (sql[i] === '-' && i + 1 < len && /[0-9]/.test(sql[i+1]))) {\n let start = i;\n if (sql[i] === '-') i++;\n while (i < len && /[0-9]/.test(sql[i])) i++;\n tokens.push({ type: 'NUMBER', value: sql.slice(start, i) });\n continue;\n }\n \n if (sql[i] === \"'\") {\n let start = i;\n i++;\n while (i < len && sql[i] !== \"'\") i++;\n if (i >= len) throw new QueryError(\"Unterminated string literal\");\n tokens.push({ type: 'STRING', value: sql.slice(start + 1, i) });\n i++; // skip closing quote\n continue;\n }\n \n if (sql[i] === '<' || sql[i] === '>' || sql[i] === '!' || sql[i] === '=') {\n let start = i;\n if (i + 1 < len && (sql[i+1] === '=' || (sql[i] === '!' && sql[i+1] === '='))) {\n i += 2;\n } else {\n i++;\n }\n tokens.push({ type: 'OP', value: sql.slice(start, i) });\n continue;\n }\n \n if (sql[i] === ',') { tokens.push({ type: 'COMMA', value: ',' }); i++; continue; }\n if (sql[i] === '*') { tokens.push({ type: 'STAR', value: '*' }); i++; continue; }\n \n throw new QueryError(`Unexpected character: ${sql[i]}`);\n }\n \n tokens.push({ type: 'EOF', value: '' });\n return tokens;\n}\n```\n\nWait, `-` handling in lexer: `(sql[i] === '-' && i + 1 < len && /[0-9]/.test(sql[i+1]))` works for negative numbers. But what if `-` appears elsewhere? The grammar doesn't allow it elsewhere. So it's fine.\n\nNow, the parser.\nI'll create a simple recursive descent parser or a sequential parser since the grammar is linear.\n\nStructure of AST:\n```typescript\ninterface SelectStmt {\n cols: string[] | '*';\n table: string;\n where: WhereClause | null;\n orderBy: { col: string; asc: boolean } | null;\n limit: number | null;\n}\n\ninterface WhereClause {\n type: 'AND' | 'OR';\n left: WhereClause | Compariso\n…[19179 chars elided]…\n= 'FROM') {\n throw new QueryError(\"Expected FROM\");\n }\n this.consume('FROM');\n\n if (this.peek().type !== 'IDENT') {\n throw new QueryError(\"Expected table name\");\n }\n const table = this.consume('IDENT').value;\n\n let where: WhereAst = null;\n if (this.peek().type === 'WHERE') {\n this.consume('WHERE');\n where = this.parseWhere();\n }\n\n let orderBy: { col: string; asc: boolean } | null = null;\n if (this.peek().type === 'ORDER') {\n this.consume('ORDER');\n if (this.peek().type !== 'BY') throw new QueryError(\"Expected BY after ORDER\");\n this.consume('BY');\n if (this.peek().type !== 'IDENT') throw new QueryError(\"Expected column name after ORDER BY\");\n const col = this.consume('IDENT').value;\n let asc = true;\n if (this.peek().type === 'ASC') {\n this.consume('ASC');\n } else if (this.peek().type === 'DESC') {\n this.consume('DESC');\n asc = false;\n }\n orderBy = { col, asc };\n }\n\n let limit: number | null = null;\n if (this.peek().type === 'LIMIT') {\n this.consume('LIMIT');\n if (this.peek().type !== 'NUMBER') throw new QueryError(\"Expected number after LIMIT\");\n const numStr = this.consume('NUMBER').value;\n const num = parseInt(numStr, 10);\n if (isNaN(num) || num < 0 || !Number.isInteger(num)) {\n throw new QueryError(\"LIMIT must be a non-negative integer\");\n }\n limit = num;\n }\n\n if (this.peek().type !== 'EOF') {\n throw new QueryError(\"Unexpected tokens after valid statement\");\n }\n\n return { cols, table, where, orderBy, limit };\n }\n\n private parseWhere(): WhereAst {\n const groups: ConditionGroup[] = [];\n const currentGroup: Comparison[] = [];\n \n currentGroup.push(this.parseComparison());\n groups.push(currentGroup);\n\n while (this.peek().type === 'AND' || this.peek().type === 'OR') {\n const op = this.peek().type;\n this.consume();\n if (op === 'OR') {\n groups.push([]);\n }\n groups[groups.length - 1",
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"reasoning": "The user wants me to implement an in-memory SQL SELECT engine in TypeScript. The previous response apparently didn't include the code properly, so I need to provide the complete `solution.ts` file.\n\nLet me carefully implement this step by step:\n\n1. Tokenizer - break SQL into tokens\n2. Parser - build AST from tokens\n3. Evaluator - execute AST against rows\n\nKey requirements:\n- Keywords are case-insensitive\n- Column names and string values are case-sensitive\n- WHERE filtering -> ORDER BY sorting -> LIMIT truncation -> column projection\n- AND binds tighter than OR\n- Stable sort\n- Type mismatch handling in comparisons\n- Missing column handling\n- Various error conditions\n\nLet me design the tokenizer:\n- Keywords: SELECT, FROM, WHERE, AND, OR, ORDER, BY, ASC, DESC, LIMIT\n- Identifiers: letters, digits, _, not starting with digit\n- Numbers: optional sign, digits\n- Strings: single-quoted\n- Operators: =, !=, <, >, <=, >=\n- Punctuation: *, comma, dot (not needed)\n\nLet me think about the token types:\n- KEYWORD\n- IDENT\n- NUMBER\n- STRING\n- OP (=, !=, <, >, <=, >=)\n- STAR\n- COMMA\n- EOF\n\nParser:\n- SELECT <cols> FROM <table> [WHERE <cond>] [ORDER BY <col> [ASC|DESC]] [LIMIT <n>]\n\nCols: * | col (, col)*\nCond: comparison (AND|OR comparison)*\n But AND binds tighter than OR, so:\n Cond: or_expr\n or_expr: and_expr (OR and_expr)*\n and_expr: comparison (AND comparison)*\n comparison: col <op> value\n\nLet me implement this carefully.\n\nFor the ORDER BY sort, I need stable sort. JavaScript's Array.sort is not guaranteed to be stable in all engines, but in modern V8 it is. However, to be safe, I should implement a stable sort or use index tracking.\n\nActually, let me re-read: \"The sort must be stable: rows that compare equal keep their relative input order.\"\n\nI'll implement a stable sort manually to be safe.\n\nLet me write the complete solution:\n\n```typescript\nexport type Row = Record<string, number | string>;\n\nexport class QueryError extends Error {}\n\n// Token types\ntype TokenType = \n | 'KEYWORD'\n | 'IDENT'\n | 'NUMBER'\n | 'STRING'\n | 'OP'\n | 'STAR'\n | 'COMMA'\n | 'EOF';\n\ninterface Token {\n type: TokenType;\n value: string;\n}\n\n// AST types\ninterface SelectStmt {\n type: 'SELECT';\n cols: string[] | '*';\n table: string;\n where: WhereClause | null;\n orderBy: OrderByClause | null;\n limit: number | null;\n}\n\ninterface WhereClause {\n type: 'WHERE';\n expr: OrExpr;\n}\n\ninterface OrExpr {\n type: 'OR';\n left: AndExpr;\n right: AndExpr;\n}\n\ninterface AndExpr {\n type: 'AND';\n left: Comparison;\n right: Comparison;\n}\n\ninterface Comparison {\n type: 'COMPARISON';\n col: string;\n op: string;\n value: number | string;\n}\n\ninterface OrderByClause {\n type: 'ORDER BY';\n col: string;\n direction: 'ASC' | 'DESC';\n}\n\n// Tokenizer\nfunction tokenize(sql: string): Token[] {\n const tokens: Token[] = [];\n let i = 0;\n \n while (i < sql.length) {\n // Skip whitespace\n if (/\\s/.test(sql[i])) {\n i++;\n continue;\n }\n \n // String literal\n if (sql[i] === \"'\") {\n let j = i + 1;\n let str = '';\n while (j < sql.length && sql[j] !== \"'\") {\n str += sql[j];\n j++;\n }\n if (j >= sql.length) {\n throw new QueryError('Unterminated string literal');\n }\n tokens.push({ type: 'STRING', value: str });\n i = j + 1;\n continue;\n }\n \n // Operators\n if (sql[i] === '!' && sql[i + 1] === '=') {\n tokens.push({ type: 'OP', value: '!=' });\n i += 2;\n continue;\n }\n if (sql[i] === '<' && sql[i + 1] === '=') {\n tokens.push({ type: 'OP', value: '<=' });\n i += 2;\n continue;\n }\n if (sql[i] === '>' && sql[i + 1] === '=') {\n tokens.push({ type: 'OP', value: '>=' });\n i += 2;\n continue;\n }\n if (sql[i] === '=') {\n tokens.push({ type: 'OP', value: '=' });\n i++;\n continue;\n }\n if (sql[i] === '<') {\n tokens.push({ type: 'OP', value: '<' });\n i++;\n continue;\n }\n if (sql[i] === '>') {\n tokens.push({ type: 'OP', value: '>' });\n i++;\n continue;\n }\n \n // Star\n if (sql[i] === '*') {\n tokens.push({ type: 'STAR', value: '*' });\n i++;\n continue;\n }\n \n // Comma\n if (sql[i] === ',') {\n tokens.push({ type: 'COMMA', value: ',' });\n i++;\n continue;\n }\n \n // Number (including negative)\n if (/[0-9]/.test(sql[i]) || (sql[i] === '-' && i + 1 < sql.length && /[0-9]/.test(sql[i + 1]))) {\n let j = i;\n if (sql[j] === '-') j++;\n while (j < sql.length && /[0-9]/.test(sql[j])) {\n j++;\n }\n tokens.push({ type: 'NUMBER', value: sql.slice(i, j) });\n i = j;\n continue;\n }\n \n // Identifier or keyword\n if (/[a-zA-Z_]/.test(sql[i])) {\n let j = i;\n while (j < sql.length && /[a-zA-Z0-9_]/.test(sql[j])) {\n j++;\n }\n const word = sql.slice(i, j);\n const upper = word.toUpperCase();\n const keywords = ['SELECT', 'FROM', 'WHERE', 'AND', 'OR', 'ORDER', 'BY', 'ASC', 'DESC', 'LIMIT'];\n if (keywords.includes(upper)) {\n tokens.push({ type: 'KEYWORD', value: upper });\n } else {\n tokens.push({ type: 'IDENT', value: word });\n }\n i = j;\n continue;\n }\n \n throw new QueryError(`Unexpected character: ${sql[i]}`);\n }\n \n tokens.push({ type: 'EOF', value: '' });\n return tokens;\n}\n\n// Parser\nclass Parser {\n private tokens: Token[];\n private pos: number;\n \n constructor(tokens: Token[]) {\n this.tokens = tokens;\n this.pos = 0;\n }\n \n private peek(): Token {\n return this.tokens[this.pos];\n }\n \n private consume(expectedType?: TokenType, expectedValue?: string): Token {\n const token = this.tokens[this.pos];\n if (expectedType && token.type !== expectedType) {\n throw new QueryError(`Expected ${expectedType}, got ${token.type} (${token.value})`);\n }\n if (expectedValue && token.value !== expectedValue) {\n throw new QueryError(`Expected ${expectedValue}, got ${token.value}`);\n }\n this.pos++;\n return token;\n }\n \n parse(): SelectStmt {\n // SELECT\n this.consume('KEYWORD', 'SELECT');\n \n // Columns\n\n…[21284 chars elided]…\ns complete. Let me write it out.\n\nWait, I also need to handle the case where `ORDER BY` is followed by something other than an IDENT. My parser consumes an IDENT after ORDER BY, so if there's a keyword or other token, it would throw. Good.\n\nAlso, I need to handle the case where `LIMIT` is followed by something other than a NUMBER. My parser consumes a NUMBER after LIMIT, so if there's an IDENT or other token, it would throw. Good.\n\nLet me also check: what about `SELECT a FROM t ORDER BY a ASC LIMIT 5`? This should work. My parser handles this.\n\nWhat about `SELECT a FROM t LIMIT 5 ORDER BY a`? This should error because ORDER BY must come before LIMIT. My parser checks for ORDER BY before LIMIT, so if LIMIT comes first, it would consume LIMIT and then check for EOF. If there's ORDER BY after LIMIT, it would throw because there are leftover tokens. Good.\n\nActually, let me trace through:\n- SELECT a FROM t LIMIT 5 ORDER BY a\n- After parsing LIMIT 5, the parser checks for EOF.\n- The next token is ORDER, which is not EOF.\n- So it throws \"Unexpected token: ORDER\".\n\nGood.\n\nI think the solution is complete. Let me write it out.\n\nHmm, one more thing. The spec says \"an unknown clause / leftover tokens after a valid statement\" should throw. My parser checks for EOF at the end, so any leftover tokens would cause an error. Good.\n\nLet me also check: what about `SELECT a FROM t WHERE`? After WHERE, the parser tries to parse a comparison, which expects an IDENT. If there's no IDENT (EOF), it would throw. Good.\n\nWhat about `SELECT a FROM t ORDER`? After ORDER, the parser expects BY. If there's no BY (EOF), it would throw. Good.\n\nWhat about `SELECT a FROM t ORDER BY`? After BY, the parser expects an IDENT. If there's no IDENT (EOF), it would throw. Good.\n\nWhat about `SELECT a FROM t LIMIT`? After LIMIT, the parser expects a NUMBER. If there's no NUMBER (EOF), it would throw. Good.\n\nI think the solution is complete. Let me write it out.\n\nActually, I realize I should also handle the case where the column list is empty. The spec says \"",
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