fix: support SQL-standard doubled quotes in string literals

MySQL/SQL allow escaping a quote inside a string by doubling it
(e.g. 'O''Hare'). The lexer only recognized backslash escapes, so
these literals were split into multiple STRING tokens and failed to
parse.

Update the STRING lexer rules to accept '' and "" inside quoted
strings, matching https://dev.mysql.com/doc/refman/5.7/en/string-literals.html

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: eaallen

src/sqlParser.jison

@@ -119,8 +119,8 @@ UNION                                                             return 'UNION'
 "}"                                                               return '}'
 ";"                                                               return ';'
 
-['](\\.|[^'])*[']                                                 return 'STRING'
-["](\\.|[^"])*["]                                                 return 'STRING'
+['](['][']|\\.|[^'])*[']                                          return 'STRING'
+["](["]["]|\\.|[^"])*["]                                          return 'STRING'
 [0][x][0-9a-fA-F]+                                                return 'HEX_NUMERIC'
 [-]?[0-9]+(\.[0-9]+)?                                             return 'NUMERIC'
 [-]?[0-9]+(\.[0-9]+)?[eE][-][0-9]+(\.[0-9]+)?                     return 'EXPONENT_NUMERIC'

test/main.test.js

@@ -468,4 +468,15 @@ describe('select grammar support', function () {
     SELECT one.name, group_concat(j.value, ', ') FROM one, json_each(one.stringArray) AS j GROUP BY one.id
     `)
   })
+
+  it('support SQL-standard doubled quotes inside string literals', function () {
+    const ast = testParser("select * from t where name = 'O''Hare'");
+    assert.equal(ast.value.where.right.value, "'O''Hare'");
+
+    const astDouble = testParser('select * from t where name = "say ""hi"""');
+    assert.equal(astDouble.value.where.right.value, '"say ""hi"""');
+
+    // empty string and backslash escapes should keep working
+    testParser("select * from t where a = '' and b = 'O\\'Hare'");
+  })
 });