Question

我有3个表，T1 T2和T3。

T1有2列：t1_id，t1_country
T2还具有2列：t2_id，t2_country

仅当(t1_id,t2_id)时，我才需要在T3中插入元组t1_country = t2_country（t1_id和t2_id是特定的并给出）。

我尝试创建3个查询：

从T1中选择特定的t1_id
从T2 t2_id中选择AND国家==我在上一个查询中找到的国家。（通过使用SELECT ... WHERE（.. AND ..））

将2个给定的ID插入到第三张表中

    pstmt = connection.prepareStatement("SELECT id , country FROM T1"+
            " where id= ?  ");
    pstmt.setInt(1,t1_id);
    ResultSet results = pstmt.executeQuery();

    pstmt2 = connection.prepareStatement("SELECT * FROM T2"+
            " where id= ? AND country=?  ");
    pstmt2.setInt(1,t2_id);
    pstmt2.setString(2,results.getString("country"));
    ResultSet results2 = pstmt2.executeQuery();

    pstmt3 = connection.prepareStatement("INSERT INTO T3" +
            " VALUES (?, ?)");
    pstmt3.setInt(1, results.getInt("id"));
    pstmt3.setInt(2, results2.getInt("id"));
    pstmt3.executeQuery();

Answer 1

您可以只执行查询

  insert into T3 
  select  t1.id, t2.id
  from  t1 
  inner join t2 on t1.id = t2.id  
     and t2.country = t1.country 
     and t1.id  = ?

从2个不同的表中选择2个特定值，然后仅在有条件的情况下将它们插入到第三个表中

1 个答案: