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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