SQL Server 子查询错误：No column name was specified for column 2 of 'a' error （转载）

问：

---

I have a MySQL query and I ran it working fine but same query showing error in SQL Server.

SQL Server query:

SELECT 
    COUNT(*) cnt 
FROM 
    (SELECT DISTINCT 
         tc_id, MAX(exn_time), STATUS 
     FROM 
         release_details a, tc_details b  
     WHERE 
         a.project = b.project 
         AND a.tc_id = b.tc_name 
         AND logicaldel = 0 
         AND a.project = 'test' 
     GROUP BY 
         tc_id, STATUS) a 
WHERE 
    a.status = 'PASS';

Error:

No column name was specified for column 2 of 'a'.

How do I modify the above query?

答：

---

Use the Alias name for your inner query.You are getting the MAX(exn_time) but not specified the name for that column that's why throwing the error. And you can use the Joins to the tables to make it more readable.

SELECT COUNT(*) cnt 
FROM (
     SELECT DISTINCT 
         tc_id,
         MAX(exn_time) AS Maxtime ,
         STATUS 
      FROM 
         release_details a JOIN tc_details b  
           ON a.project= b.project 
             AND a.tc_id = b.tc_name 
      WHERE 
           logicaldel = 0  
           AND a.project ='test' 
      GROUP BY 
         tc_id,
         STATUS 
      ) a 
 WHERE a.status='PASS';

所以记住SQL Server的子查询，每一列都要起个列名，否者会报错！

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