refactor

src/main/java/com/alibaba/druid/sql/parser/Keywords.java

@@ -41,7 +41,6 @@ public class Keywords {
         map.put("FOR", Token.FOR);
         map.put("SCHEMA", Token.SCHEMA);
         map.put("FOREIGN", Token.FOREIGN);
-        map.put("REFERENCE", Token.REFERENCE);
         map.put("REFERENCES", Token.REFERENCES);
         map.put("CHECK", Token.CHECK);
         map.put("PRIMARY", Token.PRIMARY);

src/main/java/com/alibaba/druid/sql/parser/SQLExprParser.java

@@ -214,7 +214,6 @@ public class SQLExprParser extends SQLParser {
             case USER:
             case PASSWORD:
             case DUAL:
-            case REFERENCE:
             case KEY:
             case DISTINCT:
             case LIMIT:
@@ -615,9 +614,6 @@ public class SQLExprParser extends SQLParser {
         } else if (lexer.token() == Token.IDENTIFIER) {
             identName = lexer.stringVal();
 
-            lexer.nextToken();
-        } else if (lexer.token() == Token.REFERENCE) {
-            identName = lexer.stringVal();
             lexer.nextToken();
         } else {
             throw new ParserException("error " + lexer.token());

src/main/java/com/alibaba/druid/sql/parser/Token.java

@@ -53,7 +53,6 @@ public enum Token {
     DISTINCT("DISTINCT"),
     UNIQUE("UNIQUE"), 
     FOREIGN("FOREIGN"), 
-    REFERENCE("REFERENCE"), 
     REFERENCES("REFERENCES"), 
     ALL("ALL"), 
     UNION("UNION"),