support sql ast object toString

src/main/java/com/alibaba/druid/sql/dialect/postgresql/ast/stmt/PGDeleteStatement.java

@@ -23,6 +23,7 @@ import com.alibaba.druid.sql.ast.statement.SQLDeleteStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.PGWithClause;
 import com.alibaba.druid.sql.dialect.postgresql.visitor.PGASTVisitor;
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+import com.alibaba.druid.util.JdbcConstants;
 
 public class PGDeleteStatement extends SQLDeleteStatement implements PGSQLStatement {
 
@@ -31,6 +32,10 @@ public class PGDeleteStatement extends SQLDeleteStatement implements PGSQLStatem
     private List<SQLName> using = new ArrayList<SQLName>(2);
     private boolean       returning;
     private String        alias;
+    
+    public PGDeleteStatement() {
+        super (JdbcConstants.POSTGRESQL);
+    }
 
     public boolean isReturning() {
         return returning;

src/main/java/com/alibaba/druid/sql/dialect/postgresql/ast/stmt/PGSelectStatement.java

@@ -20,16 +20,18 @@ import com.alibaba.druid.sql.ast.statement.SQLSelectStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.PGWithClause;
 import com.alibaba.druid.sql.dialect.postgresql.visitor.PGASTVisitor;
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+import com.alibaba.druid.util.JdbcConstants;
 
 public class PGSelectStatement extends SQLSelectStatement implements PGSQLStatement {
 
     private PGWithClause with;
 
     public PGSelectStatement(){
+        super(JdbcConstants.POSTGRESQL);
     }
 
     public PGSelectStatement(SQLSelect select){
-        super(select);
+        super(select, JdbcConstants.POSTGRESQL);
     }
 
     public PGWithClause getWith() {

src/main/java/com/alibaba/druid/sql/dialect/postgresql/ast/stmt/PGUpdateStatement.java

@@ -24,6 +24,7 @@ import com.alibaba.druid.sql.ast.statement.SQLUpdateStatement;
 import com.alibaba.druid.sql.dialect.postgresql.ast.PGWithClause;
 import com.alibaba.druid.sql.dialect.postgresql.visitor.PGASTVisitor;
 import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+import com.alibaba.druid.util.JdbcConstants;
 
 public class PGUpdateStatement extends SQLUpdateStatement implements PGSQLStatement {
 
@@ -34,6 +35,10 @@ public class PGUpdateStatement extends SQLUpdateStatement implements PGSQLStatem
     private List<SQLExpr>  returning = new ArrayList<SQLExpr>(2);
 
     private SQLTableSource from;
+    
+    public PGUpdateStatement(){
+        super (JdbcConstants.POSTGRESQL);
+    }
 
     public SQLTableSource getFrom() {
         return from;