Question

I want to select a bunch of data from a table using a GROUP BY clause. This works great, but I need to order the data by the date it was created, with an ORDER BY clause. My question is, can I use both these clauses within the same query, or should I be using one in a sub-query, or something else?

The original query (no modification) is this:

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

Hopefully this question is readable enough to be able to answer it.

Answer 1

The MySQL SELECT syntax is:

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]]

So yes, you can use GROUP BY and ORDER BY in the same query. What won’t order the results properly is to use ORDER BY in a sub-query. For example:

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

It doesn’t make any sense first to order the sub-query, then to make join.