加入基于各表中的

Question

这里以不同的名字出现两种常见的列是两个表中各表的例子：

客户

╔══════════╦════════════╗ 
║ GROUP_ID ║ GROUP_NAME ║ 
╠══════════╬════════════╣ 
║ abc  ║ xex  ║ 
║ def  ║ tet  ║ 
╚══════════╩════════════╝ 

队

╔════════╦════════════╗ 
║ ACT_ID ║ GROUP_NAME ║ 
╠════════╬════════════╣ 
║  44 ║ xex  ║ 
║  32 ║ tet  ║ 
╚════════╩════════════╝ 

动作

╔════╦════════════╗ 
║ ID ║ STATE ║ 
╠════╬════════════╣ 
║ 44 ║ complete ║ 
║ 58 ║ incomplete ║ 
╚════╩════════════╝ 

注意act_id表teams也存在于表actions作为id

我要选择有两列的表：group_id和group_name，其中每个group_name具有带有完整的act_idstate。

我做这样的事情：

SELECT group_id AND group_name 
FROM clients 
WHERE group_name IN (SELECT group_name 
        FROM teams, actions 
        WHERE teams.act_id = actions.id 
         AND actions.state IS complete) 

这是正确的？

我也想到了什么样

SELECT group_id AND group_name 
FROM clients 
WHERE group_name IN (SELECT group_name 
        FROM teams 
        WHERE act_id IN (SELECT id 
             FROM actions 
             WHERE teams.act_id = actions.id. 
             AND state IS complete)) 

或者是上述的正确吗？

我希望得到的表显然是这一个：

╔══════════╦════════════╗ 
║ GROUP_ID ║ GROUP_NAME ║ 
╠══════════╬════════════╣ 
║ abc  ║ xex  ║ 
╚══════════╩════════════╝ 

Answer 1

SELECT a.* 
FROM clients a 
     INNER JOIN teams b 
      ON a.group_name = b.group_name 
     INNER JOIN actions c 
      ON b.act_ID = c.id 
WHERE c.state = 'complete' 

• SQLFiddle Demo

你的SQL查询看到星号*意味着它将选择所有列都可用，在这种情况下，它将全部从表clients中选择。如果您只想选择特定列，请使用comma来区分不是AND。例如，

SELECT a.GROUP_ID, a.GROUP_NAME 
FROM clients a 
     INNER JOIN teams b 
      ON a.group_name = b.group_name 
     INNER JOIN actions c 
      ON b.act_ID = c.id 
WHERE c.state = 'complete' 

为了进一步获得更多的知识有关加入，请访问以下链接：

• Visual Representation of SQL Joins