fix: 2 correctness bugs — SQL doubled-quote escaping, SetOperator cached keys

- lexer: handle SQL-standard '' (doubled single-quote) escaping in string literals
- parser: unescape '' → ' in string value extraction
- SetOperator.rowKey: don't cache sorted keys from first row — left/right sides
  may have different column sets, causing false matches in UNION/INTERSECT/EXCEPT

Author: teamchong

src/operators.ts

@@ -1157,10 +1157,8 @@ export class SetOperator implements Operator {
     if (mode !== "union_all") this.seen = new Set();
   }
 
-  private _sortedKeys: string[] | null = null;
   private rowKey(row: Row): string {
-    if (!this._sortedKeys) this._sortedKeys = Object.keys(row).sort();
-    const keys = this._sortedKeys;
+    const keys = Object.keys(row).sort();
     let result = "";
     for (let i = 0; i < keys.length; i++) {
       if (i > 0) result += "\x00";

src/sql/lexer.ts

@@ -146,11 +146,13 @@ export function tokenize(sql: string): Token[] {
       continue;
     }
 
-    // String literals (single-quoted)
+    // String literals (single-quoted, supports '' and \' escaping)
     if (ch === "'") {
       pos++;
-      while (pos < len && sql[pos] !== "'") {
-        if (sql[pos] === "\\" && pos + 1 < len) pos++; // skip escape
+      while (pos < len) {
+        if (sql[pos] === "'" && pos + 1 < len && sql[pos + 1] === "'") { pos += 2; continue; } // doubled quote
+        if (sql[pos] === "'") break;
+        if (sql[pos] === "\\" && pos + 1 < len) pos++; // backslash escape
         pos++;
       }
       if (pos >= len) throw new SqlLexerError(`Unterminated string literal starting at position ${start}`, start);

src/sql/parser.ts

@@ -611,7 +611,7 @@ class Parser {
     // String literal
     if (this.match(TokenType.STRING)) {
       // Strip surrounding quotes
-      const raw = tok.lexeme.slice(1, -1).replace(/\\'/g, "'");
+      const raw = tok.lexeme.slice(1, -1).replace(/''/g, "'").replace(/\\'/g, "'");
       return { kind: "value", value: { type: "string", value: raw } };
     }