MySQL查詢交叉引用

Question

我正在尋找一個mysql查詢（使用php）一次遍歷每個表，並且只顯示與cross_check.lastmod中的結果不同的結果

音

guid | name | lastmod
 1   |  Joe | 2012-01-01 01:00:00
 2   |  Tom | 2012-01-02 01:00:00
 3   |  Sue | 2012-03-01 02:00:00

t_two

guid | pet  | lastmod
 4   | cat  | 2012-01-01 01:00:00
 5   | dog  | 2012-01-02 01:00:00
 6   | fish | 2012-03-01 02:00:00

t_three

guid | fruit   | lastmod
 7   |  orange | 2012-01-01 01:00:00
 8   |  pear   | 2012-01-02 01:00:00
 9   |  grape  | 2012-03-01 02:00:00

cross_check

guid | lastmod
   1 |  2012-01-01 01:00:00
   2 |  2012-01-02 01:00:00
   3 |  2012-01-01 02:00:00
   4 |  2012-01-01 01:00:00
   5 |  2012-01-02 01:00:00
   6 |  2012-01-01 02:00:00
   7 |  2012-01-01 01:00:00
   8 |  2012-01-02 01:00:00
   9 |  2012-01-01 02:00:00

查詢結果將是：

t_one => 3 | Sue   | 2012-03-01 02:00:00
t_two => 6 | fish  | 2012-03-01 02:00:00
t_three => 9 | grape | 2012-03-01 02:00:00

到目前為止，我的代碼（需要表交叉引用）

$tables = array('t_one', 't_two', 't_three');

  foreach ($tables AS $table) {

    $query = sprintf("SELECT * FROM '%s'",
    mysql_real_escape_string($table));

    $result = mysql_query($query);

  }

Answer 1

剛剛JOIN的cross_check表。

SELECT t_one.*
FROM t_one
JOIN cross_check ON t_one.guid=cross_check.guid
WHERE t_one.lastmod != cross_check.lastmod

但是，每個表仍然有一個查詢（您可以放心使用聯合，但這不會減少查詢的核心數量）。

如果要將它們合並為一個，則可以使用UNION：

[query for t_one]
 UNION
[query for t_two]
 UNION
[query for t_three]

我覺得這並沒有比執行三個不同的查詢更有效（盡管有直覺，但沒有根據）。

您也可以這樣做（盡管這僅在t_* guid之間沒有交叉的情況下才有效；如果有t_one將受到青睞，則t_two ）：

SELECT COALESCE(t_one.guid,t_two.guid,t_three.guid) AS guid
FROM cross_check
LEFT JOIN t_one ON t_one.guid=cross_check.guid 
LEFT JOIN t_two ON t_two.guid=cross_check.guid
LEFT JOIN t_three ON t_three.guid=cross_check.guid
WHERE (t_one.lastmod IS NOT NULL AND t_one.lastmod != cross_check.lastmod)
   OR (t_two.lastmod IS NOT NULL AND t_two.lastmod != cross_check.lastmod)
   OR (t_three.lastmod IS NOT NULL AND t_three.lastmod != cross_check.lastmod)

如果您想獲取標簽（而不是ID COALESCE(t_one.name, t_two.pet, t_three.fruit) AS label也可以放置COALESCE(t_one.name, t_two.pet, t_three.fruit) AS label 。

Answer 2

嘗試使用此查詢，當然替換為foreach循環中的表名。

SELECT origin.guid as guid FROM t_one as origin, cross_check as cross WHERE cross.lastmod != origin.lastmod;