add mapping support

src/main/java/com/alibaba/druid/sql/SQLUtils.java

@@ -0,0 +1,34 @@
+package com.alibaba.druid.sql;
+
+import com.alibaba.druid.sql.ast.SQLObject;
+import com.alibaba.druid.sql.dialect.mysql.visitor.MySqlOutputVisitor;
+import com.alibaba.druid.sql.dialect.oracle.visitor.OracleOutputVisitor;
+import com.alibaba.druid.sql.dialect.postgresql.visitor.PGOutputVisitor;
+
+public class SQLUtils {
+
+    public static String toMySqlString(SQLObject sqlObject) {
+        StringBuilder out = new StringBuilder();
+        sqlObject.accept(new MySqlOutputVisitor(out));
+
+        String sql = out.toString();
+        return sql;
+    }
+    
+    public static String toOracleString(SQLObject sqlObject) {
+        StringBuilder out = new StringBuilder();
+        sqlObject.accept(new OracleOutputVisitor(out));
+        
+        String sql = out.toString();
+        return sql;
+    }
+    
+    public static String toPGString(SQLObject sqlObject) {
+        StringBuilder out = new StringBuilder();
+        sqlObject.accept(new PGOutputVisitor(out));
+        
+        String sql = out.toString();
+        return sql;
+    }
+ 
+}

src/main/java/com/alibaba/druid/sql/ast/statement/SQLExprTableSource.java

@@ -27,8 +27,10 @@ public class SQLExprTableSource extends SQLTableSourceImpl {
     public SQLExprTableSource(){
 
     }
-    
-    
+
+    public SQLExprTableSource(SQLExpr expr){
+        this.expr = expr;
+    }
 
     public SQLExpr getExpr() {
         return this.expr;

src/main/java/com/alibaba/druid/sql/dialect/mysql/visitor/MySqlMappingVisitor.java

@@ -1,16 +0,0 @@
-package com.alibaba.druid.sql.dialect.mysql.visitor;
-
-import java.util.HashMap;
-import java.util.Map;
-
-import com.alibaba.druid.sql.ast.SQLExpr;
-
-public class MySqlMappingVisitor extends MySqlASTVisitorAdapter {
-
-    private final Map<String, SQLExpr> mapping = new HashMap<String, SQLExpr>();
-    
-    public void addMapping(String column, String targetExpr) {
-        
-    }
-    
-}

src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java

@@ -85,14 +85,22 @@ import com.alibaba.druid.sql.ast.statement.SQLUpdateStatement;
 
 public class SQLASTOutputVisitor extends SQLASTVisitorAdapter {
 
-    protected Appendable appender;
-    private String       indent      = "\t";
-    private int          indentCount = 0;
+    protected final Appendable appender;
+    private String             indent      = "\t";
+    private int                indentCount = 0;
 
     public SQLASTOutputVisitor(Appendable appender){
         this.appender = appender;
     }
 
+    public int getIndentCount() {
+        return indentCount;
+    }
+
+    public Appendable getAppender() {
+        return appender;
+    }
+
     public void decrementIndent() {
         this.indentCount -= 1;
     }
@@ -213,8 +221,8 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter {
         if (x.getLeft() instanceof SQLBinaryOpExpr) {
             SQLBinaryOpExpr left = (SQLBinaryOpExpr) x.getLeft();
             boolean leftRational = left.getOperator() == SQLBinaryOperator.BooleanAnd
-                    || left.getOperator() == SQLBinaryOperator.BooleanOr;
-            
+                                   || left.getOperator() == SQLBinaryOperator.BooleanOr;
+
             if (left.getOperator().priority > x.getOperator().priority) {
                 if (leftRational) {
                     incrementIndent();
@@ -222,7 +230,7 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter {
                 print('(');
                 left.accept(this);
                 print(')');
-                
+
                 if (leftRational) {
                     decrementIndent();
                 }
@@ -257,11 +265,11 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter {
                 if (rightRational) {
                     incrementIndent();
                 }
-                
+
                 print('(');
                 right.accept(this);
                 print(')');
-                
+
                 if (rightRational) {
                     decrementIndent();
                 }
@@ -985,5 +993,5 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter {
 
         return false;
     }
-    
+
 }

src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitor.java

@@ -135,7 +135,7 @@ public interface SQLASTVisitor {
 
     boolean visit(SQLExistsExpr x);
 
-    boolean visit(SQLIdentifierExpr astNode);
+    boolean visit(SQLIdentifierExpr x);
 
     boolean visit(SQLInListExpr x);
 

src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitorAdapter.java

@@ -172,7 +172,7 @@ public class SQLASTVisitorAdapter implements SQLASTVisitor {
         return true;
     }
 
-    public boolean visit(SQLIdentifierExpr astNode) {
+    public boolean visit(SQLIdentifierExpr x) {
         return true;
     }