mysql UNION 命名表属性

Question

当我执行此查询时:

select id as current from events where date = '{$result['date']}'
union all
(select id as previous from events where date < '{$result['date']}' order by date desc limit 1)
union all
(select id as next from events where date > '{$result['date']}' order by date asc limit 1)

它选择日期为 $result['date] 的 ID、低于该日期的日期以及高于该日期的日期。

所以在我的 php 代码中我需要一个像这样的数组:

Array
(
    [0] => Array
    (
        [current] => 6
    )

    [1] => Array
    (
        [previous] => 5
    )

    [2] => Array
    (
        [next] => 7
    )

)

然而，数组的结果是这样的:

Array
(
    [0] => Array
    (
        [current] => 6
    )

    [1] => Array
    (
        [current] => 5
    )

    [2] => Array
    (
        [current] => 7
    )

)

我需要 assoc 数组来描述正确的键!

尽管在我的 SQL 中我这样做

选择 ID 作为当前 选择 id 作为上一个 选择 id 作为下一个

它们都是当前？？？

有什么想法吗？

Answer 1

之所以该列同名是因为当你 UNION两个或多个查询中，最上面的查询中的列名始终是最终结果中显示的名称，而不管后续查询中的列名如何(它们基本上会被忽略)。

MySQL Union Syntax

"The column names from the first SELECT statement are used as the column names for the results returned."

---

相反，为什么不在一个查询中的单独列中获取 ID？

SELECT a.id AS current, prev.id AS previous, next.id AS next
FROM events a
CROSS JOIN 
(
    SELECT id FROM events 
    WHERE date < '{$result['date']}' 
    ORDER BY date DESC 
    LIMIT 1
) prev
CROSS JOIN 
(
    SELECT id
    FROM events 
    WHERE date > '{$result['date']}' 
    ORDER BY date 
    LIMIT 1
) next
WHERE a.date = '{$result['date']}'

这会给你类似的东西:

Array
(
    [0] => Array
    (
        [current] => 6
        [previous] => 5
        [next] => 7
    )
)