perf(postgresql,mysql): limit SQL result memory usage

lib/core/database/mysql_connection.dart

@@ -239,20 +239,22 @@ class MysqlConnection {
   Future<IResultSet> execute(
     String sql, [
     Map<String, dynamic>? params,
+    bool iterable = false,
   ]) async {
     if (!isConnected || _conn == null) {
       throw StateError('Not connected to MySQL');
     }
-    return _conn!.execute(sql, params);
+    return _conn!.execute(sql, params, iterable);
   }
 
   /// Runs [execute] with an application-level [timeout] (driver limits still apply).
   Future<IResultSet> executeWithTimeout(
     String sql, {
     Duration? timeout,
     Map<String, dynamic>? params,
+    bool iterable = false,
   }) async {
-    final f = execute(sql, params);
+    final f = execute(sql, params, iterable);
     if (timeout == null) return f;
     return f.timeout(timeout);
   }

lib/core/database/postgres_sql.dart

@@ -36,3 +36,41 @@ bool shouldSkipImplicitBegin(String sql) {
 
   return false;
 }
+
+/// Injects a `LIMIT` clause to a read-only query (SELECT, WITH, VALUES)
+/// if it does not already contain a `LIMIT` clause.
+String injectSqlLimit(String sql, int limit) {
+  final cleanSql = stripLeadingWhitespaceAndLineComments(sql);
+  final upper = cleanSql.toUpperCase();
+
+  final isSelect = upper.startsWith('SELECT') ||
+      upper.startsWith('WITH') ||
+      upper.startsWith('VALUES');
+
+  if (!isSelect) {
+    return sql;
+  }
+
+  // Check if it already has a LIMIT clause
+  final hasLimit = RegExp(r'\bLIMIT\b', caseSensitive: false).hasMatch(sql);
+  if (hasLimit) {
+    return sql;
+  }
+
+  // Strip trailing whitespace and semicolons to build the body
+  var body = sql.trimRight();
+  var suffix = '';
+
+  while (true) {
+    if (body.isEmpty) break;
+    if (body.endsWith(';')) {
+      body = body.substring(0, body.length - 1).trimRight();
+      suffix = ';$suffix';
+      continue;
+    }
+    break;
+  }
+
+  return '$body\nLIMIT $limit$suffix';
+}
+

lib/features/mysql/mysql_sql_workspace.dart

@@ -147,7 +147,7 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
       }
 
       final to = _statementTimeout();
-      final rs = await conn.executeWithTimeout(userSql, timeout: to);
+      final rs = await conn.executeWithTimeout(userSql, timeout: to, iterable: true);
 
       if (!mounted) return;
 
@@ -159,8 +159,12 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
       final rawRows = <List<Object?>>[];
       var n = 0;
       final cap = _resultMaxRows;
-      for (final row in rs.rows) {
-        if (n >= cap) break;
+      var truncated = false;
+      await for (final row in rs.rowsStream) {
+        if (n >= cap) {
+          truncated = true;
+          break;
+        }
         rawRows.add(
           List.generate(row.numOfColumns, (i) => row.colAt(i)),
         );
@@ -186,11 +190,9 @@ class _MysqlSqlWorkspaceState extends material.State<MysqlSqlWorkspace> {
               ? 'OK. Rows affected: $affected.'
               : 'Command completed.';
         } else {
-          final total = rs.numOfRows;
-          final truncated = total > cap;
           _statusLine = truncated
-              ? 'Showing first $cap of $total row(s).'
-              : '$total row(s).';
+              ? 'Showing first $cap row(s) (result capped).'
+              : '$n row(s).';
         }
         _running = false;
       });

lib/features/postgresql/postgres_sql_workspace.dart

@@ -261,7 +261,7 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
   Future<void> _execute() async {
     final userSql = _sqlController.text.trim();
     if (userSql.isEmpty) return;
-    var sql = userSql;
+    var sql = injectSqlLimit(userSql, _resultMaxRows);
 
     setState(() {
       _running = true;
@@ -323,9 +323,9 @@ class _PostgresSqlWorkspaceState extends material.State<PostgresSqlWorkspace> {
           _statusLine =
               'Command completed. Rows affected: ${result.affectedRows}.';
         } else {
-          final truncated = result.length > cap;
+          final truncated = result.length >= cap;
           _statusLine = truncated
-              ? 'Showing first $cap of ${result.length} row(s).'
+              ? 'Showing first $cap row(s) (result capped).'
               : '${result.length} row(s).';
         }
         _running = false;

test/core/database/postgres_sql_test.dart

@@ -79,4 +79,33 @@ void main() {
       expect(shouldSkipImplicitBegin('UPDATE t SET x = 1'), isFalse);
     });
   });
+
+  group('injectSqlLimit', () {
+    test('appends LIMIT to select query without limit', () {
+      expect(injectSqlLimit('SELECT * FROM users', 5000), 'SELECT * FROM users\nLIMIT 5000');
+    });
+
+    test('handles trailing semicolons', () {
+      expect(injectSqlLimit('SELECT * FROM users;', 5000), 'SELECT * FROM users\nLIMIT 5000;');
+      expect(injectSqlLimit('SELECT * FROM users;  ', 5000), 'SELECT * FROM users\nLIMIT 5000;');
+      expect(injectSqlLimit('SELECT * FROM users;;', 5000), 'SELECT * FROM users\nLIMIT 5000;;');
+    });
+
+    test('does not append LIMIT if LIMIT already exists', () {
+      expect(injectSqlLimit('SELECT * FROM users LIMIT 10', 5000), 'SELECT * FROM users LIMIT 10');
+      expect(injectSqlLimit('SELECT * FROM users limit 10;', 5000), 'SELECT * FROM users limit 10;');
+    });
+
+    test('does not modify non-select/non-read queries', () {
+      expect(injectSqlLimit('INSERT INTO users VALUES (1)', 5000), 'INSERT INTO users VALUES (1)');
+      expect(injectSqlLimit('UPDATE users SET x = 1', 5000), 'UPDATE users SET x = 1');
+    });
+
+    test('appends LIMIT to WITH query', () {
+      expect(
+        injectSqlLimit('WITH t AS (SELECT * FROM users) SELECT * FROM t;', 5000),
+        'WITH t AS (SELECT * FROM users) SELECT * FROM t\nLIMIT 5000;',
+      );
+    });
+  });
 }