fix postgresql parenthesized bug

example:
1、(select * from a)
2、(select * from a) union all select * from b;
pg以括号开头的select语句会陷入死循环。

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

@@ -31,6 +31,7 @@ public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery
     protected SQLExprTableSource        into;
     protected SQLExpr                   where;
     protected SQLSelectGroupByClause    groupBy;
+    protected boolean parenthesized = false;
 
     public SQLSelectQueryBlock(){
 
@@ -90,7 +91,15 @@ public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery
         this.from = from;
     }
 
-    @Override
+    public boolean isParenthesized() {
+		return parenthesized;
+	}
+
+	public void setParenthesized(boolean parenthesized) {
+		this.parenthesized = parenthesized;
+	}
+
+	@Override
     protected void accept0(SQLASTVisitor visitor) {
         if (visitor.visit(this)) {
             acceptChild(visitor, this.selectList);
@@ -105,6 +114,7 @@ public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery
     public int hashCode() {
         final int prime = 31;
         int result = 1;
+        result = prime * result + (Boolean.valueOf(parenthesized).hashCode());
         result = prime * result + distionOption;
         result = prime * result + ((from == null) ? 0 : from.hashCode());
         result = prime * result + ((groupBy == null) ? 0 : groupBy.hashCode());
@@ -120,6 +130,7 @@ public class SQLSelectQueryBlock extends SQLObjectImpl implements SQLSelectQuery
         if (obj == null) return false;
         if (getClass() != obj.getClass()) return false;
         SQLSelectQueryBlock other = (SQLSelectQueryBlock) obj;
+        if (parenthesized ^ other.parenthesized) return false;
         if (distionOption != other.distionOption) return false;
         if (from == null) {
             if (other.from != null) return false;

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

@@ -22,6 +22,7 @@ import com.alibaba.druid.sql.ast.SQLSetQuantifier;
 import com.alibaba.druid.sql.ast.expr.SQLIdentifierExpr;
 import com.alibaba.druid.sql.ast.statement.SQLExprTableSource;
 import com.alibaba.druid.sql.ast.statement.SQLSelectQuery;
+import com.alibaba.druid.sql.ast.statement.SQLSelectQueryBlock;
 import com.alibaba.druid.sql.ast.statement.SQLTableSource;
 import com.alibaba.druid.sql.dialect.postgresql.ast.expr.PGParameter;
 import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGFunctionTableSource;
@@ -58,6 +59,18 @@ public class PGSelectParser extends SQLSelectParser {
             return queryRest(valuesQuery);
         }
         
+        if (lexer.token() == Token.LPAREN) {
+            lexer.nextToken();
+
+            SQLSelectQuery select = query();
+			if (select instanceof SQLSelectQueryBlock) {
+				((SQLSelectQueryBlock) select).setParenthesized(true);
+			}
+            accept(Token.RPAREN);
+
+            return queryRest(select);
+        }
+        
         PGSelectQueryBlock queryBlock = new PGSelectQueryBlock();
 
         if (lexer.token() == Token.SELECT) {