使用MySQL的UNION中每个SELECT的ORDER BY不同

Question

Using PHP and MySQL, is there a way to use a different ORDER BY for each of the SELECT statements in a UNION?

SELECT * FROM the_table WHERE color = 'blue' ORDER BY price ASC LIMIT 5
UNION ALL
SELECT * FROM the_table WHERE color = 'red' ORDER BY RAND() LIMIT 10

The above statement does not work. It seems you can only do an ORDER BY on the final result set. Is there a way to do an ORDER BY on the first SELECT then a different ORDER BY on the second SELECT using UNION?

Answer 1

(SELECT * FROM the_table WHERE color = 'blue' ORDER BY price ASC LIMIT 5)
UNION ALL
(SELECT * FROM the_table WHERE color = 'red' ORDER BY RAND() LIMIT 10)

Answer 2

Please note that this does not work if you don't specify a LIMIT (though you can specify a very large dummy limit). See mysql documentation (13.2.7.3. UNION Syntax):

"Use of ORDER BY for individual SELECT statements implies nothing about the order in which the rows appear in the final result because UNION by default produces an unordered set of rows... "To cause rows in a UNION result to consist of the sets of rows retrieved by each SELECT one after the other, select an additional column in each SELECT to use as a sort column and add an ORDER BY following the last SELECT:

"(SELECT 1 AS sort_col, col1a, col1b, ... FROM t1) UNION (SELECT 2, col2a, col2b, ... FROM t2) ORDER BY sort_col; To additionally maintain sort order within individual SELECT results, add a secondary column to the ORDER BY clause:

"(SELECT 1 AS sort_col, col1a, col1b, ... FROM t1) UNION (SELECT 2, col2a, col2b, ... FROM t2) ORDER BY sort_col, col1a;"