sql parser refactor

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

@@ -17,7 +17,6 @@ package com.alibaba.druid.sql.parser;
 
 import java.util.HashMap;
 import java.util.Map;
-import java.util.Set;
 
 /**
  * @author wenshao<szujobs@hotmail.com>

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

@@ -368,6 +368,10 @@ public class SQLExprParser extends SQLParser {
                 sqlExpr = new SQLIdentifierExpr("RIGHT");
                 lexer.nextToken();
                 break;
+            case DATABASE:
+                sqlExpr = new SQLIdentifierExpr("DATABASE");
+                lexer.nextToken();
+                break;
             case LOCK:
                 sqlExpr = new SQLIdentifierExpr("LOCK");
                 lexer.nextToken();