php - 从 4 个表中找到唯一的最小和最大日期 - php

Question

我正在使用 wordpress 并有 4 个自定义表格。他们每个人看起来像这样:

Table1       Table2        Table3        Table4

date         date          date          date
2016-07-21   2016-11-13    2016-10-19    2016-11-18  
2016-09-16   2016-10-27    2016-11-13    2016-10-25
2016-09-09   2016-09-30    2016-07-15    2016-09-28
2016-11-11   2016-08-19    2016-11-17    2016-10-24

我需要找到这 4 个表的最小日期和这 4 个表的最大日期。我尝试通过以下代码来做到这一点:

$minViews = $wpdb->get_results("
SELECT MIN(date) as min_date FROM Table1 UNION 
SELECT MIN(date) as min_date FROM Table2 UNION 
SELECT MIN(date) as min_date FROM Table3 UNION 
SELECT MIN(date) as min_date FROM Table4");

$maxViews = $wpdb->get_results("
SELECT MAX(date) as max_date FROM Table1 UNION 
SELECT MAX(date) as max_date FROM Table2 UNION 
SELECT MAX(date) as max_date FROM Table3 UNION 
SELECT MAX(date) as max_date FROM Table4");

但上面的查询返回每个表的最小和最大日期。但我需要找到所有 4 个表 的最小日期和所有 4 个表 的最大日期。

Answer 1

您始终可以在 FROM 子句中使用子查询:

SELECT MIN(date), MAX(date) FROM
(
    SELECT date FROM Table1
    UNION SELECT date FROM Table2
    UNION SELECT date FROM Table3
    UNION SELECT date FROM Table4
) AS sq;