帶聯合和順序的sql語句

Question

這個SQL很好用，但是一旦我想使用ORDER BY id來排序我的選擇，它將無法工作。 所有這些表都有一個id類型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

• 必須在每個選擇上都包含ID以保持結構相等。
• 然后將所有內容放在解析之間，並在需要時分配別名。 ( a union b union c ) as ALIAS
• 最后做的select上表的別名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的組件中使用order by ，您需要將子查詢括在括號中。 然后，您可以在最后添加order by 。 因此，此結構將起作用：

(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：使用此結構時，如果要按順序進行排序，則需要在列列表中包含id 。