feat: add DB2 special register CURRENT TIMEZONE

fixes #1949

Signed-off-by: Andreas Reichel <andreas@manticore-projects.com>

Author: manticore-projects

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

@@ -427,6 +427,7 @@ TOKEN: /* SQL Keywords. prefixed with K_ to avoid name clashes */
                          ("CURRENT" ( "_" | (" ")+ ) "TIMESTAMP")
                          | ("CURRENT" ( "_" | (" ")+ ) "TIME")
                          | ("CURRENT" ( "_" | (" ")+ ) "DATE")
+                         | ("CURRENT" ( "_" | (" ")+ ) "TIMEZONE")
                        ) ( "()" )?>
 |   <K_TIMEOUT:"TIMEOUT">
 |   <K_TRIM:"TRIM">

src/test/java/net/sf/jsqlparser/statement/select/DB2Test.java

@@ -0,0 +1,13 @@
+package net.sf.jsqlparser.statement.select;
+
+import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.test.TestUtils;
+import org.junit.jupiter.api.Test;
+
+public class DB2Test {
+    @Test
+    void testDB2SpecialRegister() throws JSQLParserException {
+        String sqlStr = "SELECT * FROM TABLE1 where COL_WITH_TIMESTAMP <= CURRENT TIMESTAMP - CURRENT TIMEZONE";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+    }
+}