improved sql parser, bug fixed for parent is null

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

@@ -48,6 +48,13 @@ public class PGWithQuery extends PGSQLObjectImpl {
         return columns;
     }
 
+    public void addColumn(SQLExpr column) {
+        if (column != null) {
+            column.setParent(this);
+        }
+        this.columns.add(column);
+    }
+    
     @Override
     public void accept0(PGASTVisitor visitor) {
         if (visitor.visit(this)) {

src/main/java/com/alibaba/druid/sql/dialect/postgresql/parser/PGSQLStatementParser.java

@@ -254,7 +254,7 @@ public class PGSQLStatementParser extends SQLStatementParser {
 
             for (;;) {
                 SQLExpr expr = this.exprParser.expr();
-                withQuery.getColumns().add(expr);
+                withQuery.addColumn(expr);
                 if (lexer.token() == Token.COMMA) {
                     lexer.nextToken();
                     continue;