sql从Java调用PostgreSQL中的存储过程

Question

我已经编写了一个我想用Java调用的存储过程。但我认为它无法处理我传递的查询。以下是我的java代码：

String QUERY_LOCATION = "select (license_plate) as test from carInst( (select     category_name from reservation where rid = ?) , (select lname from reservation where rid =  ?))";  
        //PreparedStatement check_location = null;
        PreparedStatement check_location = connection.prepareStatement(QUERY_LOCATION);
        check_location.setInt(1, rid);
        check_location.setInt(2, rid);
        rs = check_location.executeQuery();
        if (rs.next()) {
            System.out.print("Car found: "+rs.getString("test")+"\n");
            license_plate = rs.getString("test");
            update_reservation.setString(5, license_plate);

            bool = false;
        } else {
            System.out
                    .print("There is no car available\n");
        }

下面是我用PL/pgSQL（PostgreSQL）编写的存储过程：

CREATE OR REPLACE FUNCTION carInst(cname varchar(20), loc varchar(20) ) 
RETURNS TABLE (license_plate varchar(6) ) AS $$
BEGIN 
    DECLARE cur CURSOR 
        FOR SELECT carinstance.license_plate, carmodel.category_name, carinstance.lname FROM carinstance,carmodel 
            WHERE carinstance.mid = carmodel.mid ;                  
BEGIN 
    FOR rec IN cur LOOP
        RETURN QUERY SELECT distinct carinstance.license_plate FROM Carinstance 
            WHERE rec.category_name  = cname
                AND rec.lname = loc
                AND rec.license_plate=carinstance.license_plate;
        END LOOP;
    END; 
END;
$$ LANGUAGE plpgsql;

当我用Java运行代码时，print语句为Car found打印一个空值。我真的很想在这里得到一些帮助

Answer 1

问题

• 最重要的是，LOOP中的查询毫无意义。您可以从carinstance中选择行，但所有条件都在rec上。多次选择所有行

• 太多了FOR没有END，只有LOOP有

• 每当你想在plpgsql中使用显式游标时，就到此为止。很可能你做错了。FOR循环仍然有一个隐式游标

• 别惹mixed case identifiers without double quotes。我将所有标识符转换为小写

• 您可以使用一个简单的查询，分散在一个光标和另一个查询上。这一切都可以简单得多

解决方案

请尝试以下简单的SQL函数：

CREATE OR REPLACE FUNCTION car_inst(_cname text, _loc text) 
  RETURNS TABLE (license_plate text) AS
$func$
   SELECT DISTINCT ci.license_plate
   FROM   carmodel    cm
   JOIN   carinstance ci USING (mid)
   WHERE  cm.category_name  = $1
   AND    ci.lname = $2
$func$ LANGUAGE sql;

电话：

"SELECT license_plate AS test FROM car_inst(
         (SELECT category_name FROM reservation WHERE rid = ?)
        ,(SELECT lname FROM reservation WHERE rid = ?))";  

或者将其全部构建到您的功能中：

CREATE OR REPLACE FUNCTION car_inst(_cname text, _loc text) 
  RETURNS TABLE (license_plate text) AS
$func$
   SELECT DISTINCT ci.license_plate
   FROM   carmodel    cm
   JOIN   carinstance ci USING (mid)
   JOIN   reservation r1 ON r1.category_name = cm.category_name
   JOIN   reservation r2 ON r2.lname = ci.lname
   WHERE  r1.rid = $1
   AND    r2.rid = $2;
$func$ LANGUAGE sql;

电话：

"SELECT license_plate AS test FROM car_inst(? , ?)";  

记住：OUT参数license_plate在函数体的任何地方都可见。因此，必须始终对相同名称的列进行表限定，以防止命名冲突

DISTINCT可能是多余的，也可能不是多余的