fix: allow GROUPS as identifier by making it a non-reserved keyword (#2473) (#2474)

Signed-off-by: 付典 <fudianchn@gmail.com>

Author: fudianchn

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

@@ -1287,6 +1287,7 @@ String NonReservedWord() :
       | tk=<K_FULLTEXT:"FULLTEXT">
       | tk=<K_FUNCTION:"FUNCTION">
       | tk=<K_GRANT:"GRANT">
+      | tk=<K_GROUPS:"GROUPS">
       | tk=<K_GROUP_CONCAT:"GROUP_CONCAT">
       | tk=<K_GUARD:"GUARD">
       | tk=<K_HASH:"HASH">
@@ -1577,7 +1578,6 @@ TOKEN: /* Reserved SQL Keywords and structural tokens */
 |   <K_GLOBAL:"GLOBAL">
 |   <K_GROUP:"GROUP">
 |   <K_GROUPING:"GROUPING">
-|   <K_GROUPS:"GROUPS">
 |   <K_HAVING:"HAVING">
 |   <K_IF:"IF">
 |   <K_IIF:"IIF">

src/test/java/net/sf/jsqlparser/statement/KeywordsTest.java

@@ -51,4 +51,15 @@ public void testCombinedTokenKeywords() throws JSQLParserException {
         String sqlStr = "SELECT current_date(3)";
         assertSqlCanBeParsedAndDeparsed(sqlStr, true);
     }
+
+    // #2473: GROUPS is a non-reserved keyword in PostgreSQL and must stay usable as an
+    // identifier, although it also introduces the GROUPS window frame unit.
+    @Test
+    public void testGroupsAsIdentifier() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("SELECT groups FROM mytable", true);
+        assertSqlCanBeParsedAndDeparsed("SELECT * FROM groups", true);
+        assertSqlCanBeParsedAndDeparsed("SELECT a AS groups FROM mytable", true);
+        assertSqlCanBeParsedAndDeparsed("SELECT a groups FROM mytable", true);
+        assertSqlCanBeParsedAndDeparsed("CREATE TABLE mytable (groups INT)", true);
+    }
 }