improved sql parser.

src/main/java/com/alibaba/druid/sql/builder/FunctionBuilder.java

@@ -0,0 +1,78 @@
+/*
+ * Copyright 1999-2017 Alibaba Group Holding Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.alibaba.druid.sql.builder;
+
+import com.alibaba.druid.sql.ast.SQLExpr;
+import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
+import com.alibaba.druid.util.JdbcConstants;
+
+/**
+ * Created by wenshao on 09/07/2017.
+ */
+public class FunctionBuilder {
+    private final String dbType;
+
+    public FunctionBuilder(String dbType) {
+        this.dbType = dbType;
+    }
+
+    // for character function
+    public SQLMethodInvokeExpr length(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("length", null, expr);
+    }
+
+    public SQLMethodInvokeExpr lower(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("lower", null, expr);
+    }
+
+    public SQLMethodInvokeExpr upper(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("upper", null, expr);
+    }
+
+    public SQLMethodInvokeExpr substr(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("substr", null, expr);
+    }
+
+    public SQLMethodInvokeExpr ltrim(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("ltrim", null, expr);
+    }
+
+    public SQLMethodInvokeExpr rtrim(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("rtrim", null, expr);
+    }
+
+    public SQLMethodInvokeExpr trim(SQLExpr expr) {
+        return new SQLMethodInvokeExpr("trim", null, expr);
+    }
+
+    public SQLMethodInvokeExpr ifnull(SQLExpr expr1, SQLExpr expr2) {
+        if (JdbcConstants.ALIYUN_ADS.equals(dbType)
+                || JdbcConstants.PRESTO.equals(dbType)
+                || JdbcConstants.ODPS.equals(dbType)) {
+            return new SQLMethodInvokeExpr("coalesce", null, expr1, expr2);
+        }
+
+        if (JdbcConstants.ORACLE.equals(dbType)) {
+            return new SQLMethodInvokeExpr("nvl", null, expr1, expr2);
+        }
+
+        if (JdbcConstants.SQL_SERVER.equals(dbType)) {
+            return new SQLMethodInvokeExpr("isnull", null, expr1, expr2);
+        }
+
+        return new SQLMethodInvokeExpr("ifnull", null, expr1, expr2);
+    }
+}