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我正在使用Drupal 7,并且必须在多个表上创建一个联合。对于工会工作的一些条件必须满足:
- 相同的列数
- 相同的数据类型
- 相同为了
,某些表失一列,因此为了弥补这一点,我只是像这样添加它:$query->addExpression(':field_1', 'field_1', array(':field_1' => NULL));
。因此,在这种情况下,条件1 & 2得到满足,但选择字段的顺序是不同的。
参见下文例如:
$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));
}
$query_3->fields('t3', array('field_2'));
,其结果是:
// dpq($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
将不能保证场的位置是在你期望的那样。查看已使用addExpression
的第3个查询的转储。关于如何解决这个问题的任何想法?