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我正在使用Drupal 7,並且必須在多個表上創建一個聯合。對於工會工作的一些條件必須滿足:
- 相同的列數
- 相同的數據類型
- 相同爲了
,某些表失一列,因此爲了彌補這一點,我只是像這樣添加它:$query->addExpression(':field_1', 'field_1', array(':field_1' => NULL));
。因此,在這種情況下,條件1 & 2得到滿足,但選擇字段的順序是不同的。
參見下文例如:
$query_1 = db_select('table_one', 't1');
$query_1->fields('t1', array('field_1', 'field_2'));
$query_2 = db_select('table_two', 't2');
if (true) {
$query_2->fields('t2', array('field_1'));
} else {
$query_2->addExpression(':field_1', 'field_1', array(':field_1' => NULL));
}
$query_2->fields('t2', array('field_2'));
$query_3 = db_select('table_three', 't3');
if (false) {
$query_3->fields('t3', array('field_1'));
} else {
$query_3->addExpression(':field_1', 'field_1', array(':field_1' => NULL));
}
$query_3->fields('t3', array('field_2'));
,其結果是:
// dpq($query_1);
SELECT t1.field_1 AS field_1, t1.field_2 AS field_2
FROM {table_one} t1
// dpq($query_2);
SELECT t2.field_1 AS field_1, t2.field_2 AS field_2
FROM {table_two} t2
// dpq($query_3);
SELECT t3.field_2 AS field_2, '' AS field_1
FROM {table_three} t3
// dpq($query_1->union($query_2)->union($query_3));
SELECT t1.field_1 AS field_1, t1.field_2 AS field_2
FROM {table_one} t1
UNION SELECT t2.field_1 AS field_1, t2.field_2 AS field_2
FROM {table_two} t2
UNION SELECT t3.field_2 AS field_2, '' AS field_1
FROM {table_three} t3
似乎使用$query->addExpression
將不能保證場的位置是在你期望的那樣。查看已使用addExpression
的第3個查詢的轉儲。關於如何解決這個問題的任何想法?