[FLINK-22654][sql-parser] Fix SqlCreateTable#toString()/unparse() lose CONSTRAINTS and watermarks

This closes #15918

Author: zjuwangg

flink-table/flink-sql-parser/src/main/java/org/apache/flink/sql/parser/ddl/SqlCreateTable.java

@@ -266,7 +266,7 @@ public void unparse(SqlWriter writer, int leftPrec, int rightPrec) {
             writer.keyword("IF NOT EXISTS");
         }
         tableName.unparse(writer, leftPrec, rightPrec);
-        if (columnList.size() > 0) {
+        if (columnList.size() > 0 || tableConstraints.size() > 0 || watermark != null) {
             SqlWriter.Frame frame =
                     writer.startList(SqlWriter.FrameTypeEnum.create("sds"), "(", ")");
             for (SqlNode column : columnList) {

flink-table/flink-sql-parser/src/test/java/org/apache/flink/sql/parser/FlinkSqlParserImplTest.java

@@ -816,6 +816,35 @@ public void testCreateTableWithLikeClause() {
         sql(sql).ok(expected);
     }
 
+    @Test
+    public void testCreateTableWithLikeClauseWithoutColumns() {
+        final String sql =
+                ""
+                        + "create TEMPORARY table source_table (\n"
+                        + "   WATERMARK FOR ts AS ts - INTERVAL '5' SECOND\n"
+                        + ") with (\n"
+                        + "  'scan.startup.mode' = 'specific-offsets',\n"
+                        + "  'scan.startup.specific-offsets' = 'partition:0,offset:1169129'\n"
+                        + ") like t_order_course (\n"
+                        + "   OVERWRITING  WATERMARKS\n"
+                        + "   OVERWRITING OPTIONS\n"
+                        + "   EXCLUDING CONSTRAINTS\n"
+                        + ")";
+        final String expected =
+                "CREATE TEMPORARY TABLE `SOURCE_TABLE` (\n"
+                        + "  WATERMARK FOR `TS` AS (`TS` - INTERVAL '5' SECOND)\n"
+                        + ") WITH (\n"
+                        + "  'scan.startup.mode' = 'specific-offsets',\n"
+                        + "  'scan.startup.specific-offsets' = 'partition:0,offset:1169129'\n"
+                        + ")\n"
+                        + "LIKE `T_ORDER_COURSE` (\n"
+                        + "  OVERWRITING WATERMARKS\n"
+                        + "  OVERWRITING OPTIONS\n"
+                        + "  EXCLUDING CONSTRAINTS\n"
+                        + ")";
+        sql(sql).ok(expected);
+    }
+
     @Test
     public void testCreateTemporaryTable() {
         final String sql =
@@ -851,6 +880,25 @@ public void testCreateTableWithNoColumns() {
         sql(sql).ok(expected);
     }
 
+    @Test
+    public void testCreateTableWithOnlyWaterMark() {
+        final String sql =
+                "create table source_table (\n"
+                        + "  watermark FOR ts AS ts - interval '3' second\n"
+                        + ") with (\n"
+                        + "  'x' = 'y',\n"
+                        + "  'abc' = 'def'\n"
+                        + ")";
+        final String expected =
+                "CREATE TABLE `SOURCE_TABLE` (\n"
+                        + "  WATERMARK FOR `TS` AS (`TS` - INTERVAL '3' SECOND)\n"
+                        + ") WITH (\n"
+                        + "  'x' = 'y',\n"
+                        + "  'abc' = 'def'\n"
+                        + ")";
+        sql(sql).ok(expected);
+    }
+
     @Test
     public void testDropTable() {
         final String sql = "DROP table catalog1.db1.tbl1";