带联合和顺序的sql语句

Question

这个SQL很好用，但是一旦我想使用ORDER BY id来排序我的选择，它将无法工作。 所有这些表都有一个id类型int 。

$sth = $this->db->prepare("SELECT r1, r2, r3, r4
    FROM table1
        WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0,20 
    UNION
        SELECT   r1, r2, r3, r4  FROM table2
            WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0,20 
    UNION
        SELECT   r1, r2, r3, r4  FROM table3
            WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0,20 
    UNION
        SELECT   r1, r2, r3, r4  FROM table4
            WHERE name LIKE '%{$key}%'  AND status = 1 LIMIT 0,20 ");

$sth->execute();
$data = $sth->fetchAll();

Answer 1

• 必须在每个选择上都包含ID以保持结构相等。
• 然后将所有内容放在解析之间，并在需要时分配别名。 ( a union b union c ) as ALIAS
• 最后做的select上表的别名SELECT * FROM ALIAS ORDER BY ID

。

$sth = $this->db->prepare(" SELECT * FROM (
     SELECT   id, r1, r2, r3, r4  FROM table1 WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0,20 
     UNION
     SELECT   id, r1, r2, r3, r4  FROM table2 WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0,20 
     UNION
     SELECT   id, r1, r2, r3, r4  FROM table3 WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0,20 
     UNION
     SELECT   id, r1, r2, r3, r4  FROM table4 WHERE name LIKE '%{$key}%'  AND status = 1 LIMIT 0,20 
) as Alias ORDER BY ID");
$sth->execute();
$data = $sth->fetchAll();

Answer 2

要在union的组件中使用order by ，您需要将子查询括在括号中。 然后，您可以在最后添加order by 。 因此，此结构将起作用：

(SELECT id, r1, r2, r3, r4 FROM table1 WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0, 20
) UNION
(SELECT id, r1, r2, r3, r4  FROM table2 WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0, 20 
) UNION
(SELECT id, r1, r2, r3, r4  FROM table3 WHERE name LIKE '%{$key}%' AND status = 1 LIMIT 0, 20 
) UNION
(SELECT id, r1, r2, r3, r4  FROM table4 WHERE name LIKE '%{$key}%'  AND status = 1 LIMIT 0, 20)
ORDER BY id;

注意：使用此结构时，如果要按顺序进行排序，则需要在列列表中包含id 。