fix: allow scalar subquery as LIMIT row count (#2359)

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -5383,8 +5383,19 @@ PlainSelect PlainSelect() #PlainSelect:
     [ LOOKAHEAD(<K_ORDER> <K_BY>) orderByElements = OrderByElements() { plainSelect.setOrderByElements(orderByElements); } ]
     [ LOOKAHEAD(2) forClause = ForClause() {plainSelect.setForClause(forClause);} ]
     [ LOOKAHEAD(2) <K_EMIT> <K_CHANGES> { plainSelect.setEmitChanges(true); } ]
-    [ LOOKAHEAD(7) limit = LimitBy() { plainSelect.setLimitBy(limit);  } ]
-    [ LOOKAHEAD(<K_LIMIT>) limit = LimitWithOffset() { plainSelect.setLimit(limit);    } ]
+    // Parse the LIMIT row count once (this accepts a parenthesized subquery too), then
+    // optionally attach ClickHouse's `LIMIT ... BY ...`. Checking BY right after the limit
+    // expression avoids a numeric LOOKAHEAD, which cannot see past a long parenthesized
+    // subquery and would wrongly commit to LIMIT BY (issue #2359).
+    [ LOOKAHEAD(<K_LIMIT>) limit = LimitWithOffset()
+        [ LOOKAHEAD(<K_BY>) <K_BY> expressionList = ExpressionList() { limit.setByExpressions(expressionList); } ]
+        {
+            if (limit.getByExpressions() != null) {
+                plainSelect.setLimitBy(limit);
+            } else {
+                plainSelect.setLimit(limit);
+            }
+        } ]
     [ LOOKAHEAD(<K_OFFSET>) offset = Offset() { plainSelect.setOffset(offset);    } ]
 	[ LOOKAHEAD(<K_LIMIT>, { limit==null }) limit = LimitWithOffset() { plainSelect.setLimit(limit);    } ]
     [ LOOKAHEAD(<K_FETCH>) fetch = Fetch() { plainSelect.setFetch(fetch);    } ]
@@ -6773,24 +6784,6 @@ Limit PlainLimit() #PlainLimit:
     }
 }
 
-/**
- * Clickhouse LIMIT BY
- * @see <a href='https://clickhouse.com/docs/en/sql-reference/statements/select'>SELECT Query</a>
- */
-Limit LimitBy():
-{
-    Limit limit;
-    ExpressionList byExpressions;
-}
-{
-    limit = LimitWithOffset()
-    <K_BY> byExpressions = ExpressionList()
-    {
-        limit.setByExpressions(byExpressions);
-        return limit;
-    }
-}
-
 Offset Offset():
 {
     Offset offset = new Offset();

src/test/java/net/sf/jsqlparser/expression/LimitExpressionTest.java

@@ -11,6 +11,7 @@
 
 import net.sf.jsqlparser.JSQLParserException;
 import net.sf.jsqlparser.parser.CCJSqlParserUtil;
+import net.sf.jsqlparser.statement.select.ParenthesedSelect;
 import net.sf.jsqlparser.statement.select.PlainSelect;
 import net.sf.jsqlparser.test.TestUtils;
 import org.junit.jupiter.api.Assertions;
@@ -31,6 +32,38 @@ public void testIssue933() throws JSQLParserException {
                 "SELECT * FROM tmp3 LIMIT (SELECT 2)", true);
     }
 
+    @Test
+    public void testIssue2359() throws JSQLParserException {
+        // PostgreSQL allows any expression, including a scalar subquery, as the LIMIT row
+        // count. A long parenthesized subquery used to fail because the ClickHouse
+        // "LIMIT ... BY ..." branch was chosen by a numeric LOOKAHEAD that cannot see past
+        // the subquery.
+        String sql = "WITH some_table AS (SELECT 1 AS some_column), "
+                + "another_table AS (SELECT 'some_value' AS condition_column) "
+                + "SELECT some_column FROM some_table ORDER BY some_column "
+                + "LIMIT (SELECT COUNT(*) FROM another_table WHERE condition_column = 'some_value')";
+
+        PlainSelect plainSelect = (PlainSelect) CCJSqlParserUtil.parse(sql);
+        Assertions.assertTrue(
+                plainSelect.getLimit().getRowCount() instanceof ParenthesedSelect);
+        Assertions.assertNull(plainSelect.getLimitBy());
+
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sql, true);
+
+        // A function wrapping a scalar subquery must work as the row count too.
+        TestUtils.assertSqlCanBeParsedAndDeparsed(
+                "SELECT a FROM t LIMIT GREATEST(0, (SELECT COUNT(*) FROM u WHERE c = 'x'))",
+                true);
+    }
+
+    @Test
+    public void testLimitByClickHouseUnchanged() throws JSQLParserException {
+        // ClickHouse "LIMIT ... BY ..." must keep parsing and round-tripping after the LIMIT
+        // row-count disambiguation was rewritten (issue #2359).
+        TestUtils.assertSqlCanBeParsedAndDeparsed("SELECT id FROM t LIMIT 5 BY id", true);
+        TestUtils.assertSqlCanBeParsedAndDeparsed("SELECT id FROM t LIMIT 2, 5 BY id", true);
+    }
+
     @Test
     public void testIssue1373() throws JSQLParserException {
         TestUtils.assertSqlCanBeParsedAndDeparsed(