同一个MySQL查询中的GROUP BY和ORDER BY？

Question

我想使用GROUP BY子句从表中选择一堆数据.这很好用,但我需要按照创建日期的顺序对数据进行排序ORDER BY.我的问题是,我可以在同一个查询中使用这两个子句,还是应该在子查询中使用其中一个,还是其他什么？

原始查询(无修改)是这样的:

SELECT * 
FROM table 
WHERE tag_draft=0 
AND 
(
    (target_id=2 AND tag_del_target=0) 
    OR (source_id=2 AND tag_del_source=0)
) 
AND updated IN
(
    SELECT MAX(updated) 
    FROM table 
    GROUP BY thread_id
) 
ORDER BY updated DESC

希望这个问题足够可读,以便能够回答它.

Answer 1

MySQL SELECT语法是:

SELECT
    [ALL | DISTINCT | DISTINCTROW ]
      [HIGH_PRIORITY]
      [STRAIGHT_JOIN]
      [SQL_SMALL_RESULT] [SQL_BIG_RESULT] [SQL_BUFFER_RESULT]
      [SQL_CACHE | SQL_NO_CACHE] [SQL_CALC_FOUND_ROWS]
    select_expr [, select_expr ...]
    [FROM table_references
    [WHERE where_condition]
    [GROUP BY {col_name | expr | position}
      [ASC | DESC], ... [WITH ROLLUP]]
    [HAVING where_condition]
    [ORDER BY {col_name | expr | position}
      [ASC | DESC], ...]
    [LIMIT {[offset,] row_count | row_count OFFSET offset}]
    [PROCEDURE procedure_name(argument_list)]
    [INTO OUTFILE 'file_name' export_options
      | INTO DUMPFILE 'file_name'
      | INTO var_name [, var_name]]
    [FOR UPDATE | LOCK IN SHARE MODE]]

所以是的,你可以在同一个查询中使用GROUP BY和ORDER BY.什么不能正确排序结果是在子查询中使用ORDER BY.例如:

SELECT 
       something
FROM 
       aTable 
JOIN 
       (SELECT myID FROM anotherTable ORDER BY myID) as bTable 
  ON aTable.ID=bTable.myID

首先订购子查询然后进行连接是没有任何意义的.