Question

表'2_1_journal'

NumberRenamed
-------------
 1
 2
 3

表'2_1_paidused'

NumberRenamed
-------------
 1
 2

想要从每个表中选择最后一个值，并获得具有2个值的数组。

基于示例，创建了这样的代码

SELECT 2_1_journal.NumberRenamed, 2_1_paidused.NumberRenamed 

FROM 2_1_journal

LEFT JOIN 2_1_paidused ON 2_1_journal.NumberRenamed = 2_1_paidused.NumberRenamed

ORDER BY NumberRenamed DESC LIMIT 1


$stmt->execute();
$ArrayWithTwoNumbers = $stmt->fetchColumn();

但是得到错误SQLSTATE[23000]: Integrity constraint violation: 1052 Column 'NumberRenamed' in order clause is ambiguous。

如果删除ORDER BY NumberRenamed DESC LIMIT 1获取值1（来自2_1_journal.NumberRenamed的第一个值）。

请建议需要纠正的内容。

简单的方法是使用SELECT进行2次查询。但据我所知，更好地节省资源以使用一个查询....

已更改为ORDER BY 2_1_journal.NumberRenamed DESC LIMIT 1并获得123

已更改为

(SELECT NumberRenamed FROM 2_1_journal
UNION
SELECT NumberRenamed FROM 2_1_paidused)

ORDER BY NumberRenamed DESC LIMIT 1

获取SQLSTATE[42000]: Syntax error or access violation: 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'UNION SELECT NumberRenamed FROM 2_1_paidused) ORDER BY NumberRenamed DESC LI' at line 2

已更改为

(SELECT NumberRenamed FROM 2_1_journal )
UNION ALL
(SELECT NumberRenamed FROM 2_1_paidused)

ORDER BY NumberRenamed DESC LIMIT 1

没有错误，但结果不符合预期（从表2_1_paidused获取最后一个值）。如何从表2_1_journal中获取最后一个值？

似乎这是解决方案

(SELECT NumberRenamed as Number1 FROM 2_1_journal ORDER BY Number1 DESC LIMIT 1)
UNION
(SELECT NumberRenamed as Number2 FROM 2_1_paidused ORDER BY Number2 DESC LIMIT 1)

和$stmt->fetchAll();

获取

[0] => Array
    (
        [Number1] => 3
        [0] => 3
    )

[1] => Array
    (
        [Number1] => 2
        [0] => 2
    )

值正确（如预期的那样）。但是为什么在[0]和[1]中有[Number1]？预计在[1] [Number2]

Answer 1

测试类似：

select
  (select max(NumberRenamed) from 2_1_journal) max1,
  (select max(NumberRenamed) from 2_1_paidused) max2

它比2个不同的查询好一点，唯一的区别是它有1个远程调用（网络开销），但使用2个不同的查询会产生2个远程调用。

Answer 2

添加任意一个表名，如2_1_journal.NumberRenamed

SELECT 2_1_journal.NumberRenamed, 2_1_paidused.NumberRenamed 

FROM 2_1_journal

LEFT JOIN 2_1_paidused ON 2_1_journal.NumberRenamed = 2_1_paidused.NumberRenamed

ORDER BY 2_1_journal.NumberRenamed DESC LIMIT 1

mysql SELECT最后一个值来自2个表，2列（同名）

2 个答案: