Question

我试图这样做

SELECT 
  table1.*,
  table2.id as t2id 
FROM 
  table1 as t1 
INNER JOIN table2 as t2 
  ON t2.field1 = t1.field2 
  AND t1.field2 = 'value'
  AND IF(SELECT COUNT(*) FROM table2 WHERE id = 10 > 0)

错误说

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 

'SELECT COUNT(*) FROM table2 WHERE id = 10 > 0) LIMIT ' at line 1

我知道错误与if条件一样，当我删除它，它的工作原理，但我的想法是如果它不成功，选择将返回一个空值，即它没有找到表格中id为10的表格中的任何内容

任何帮助将不胜感激的家伙：）

Answer 1

你错过了if。的“then”部分。

它看起来像IF（条件，然后，否则），但你只是在没有任何输出的情况下做这个条件。

以这种方式尝试：

AND IF((SELECT COUNT(*) FROM table2 WHERE id = 10) > 0, 'true', 'false')

Answer 2

尝试删除IF。

SELECT 
  table1.*,
  table2.id as t2id 
FROM 
  table1 as t1 
INNER JOIN table2 as t2 
  ON t2.field1 = t1.field2 
  AND t1.field2 = 'value'
  AND (SELECT COUNT(*) FROM table2 WHERE id = 10) > 0;

Answer 3

试试这个（确保你在同一个会话上执行查询）：

SELECT COUNT(*) INTO @COUNTER FROM table2 WHERE id = 10 ;

SELECT 
  table1.*,
  table2.id as t2id 
FROM 
  table1 as t1 
INNER JOIN table2 as t2 
  ON t2.field1 = t1.field2 
  AND t1.field2 = 'value'
  AND @COUNTER > 0 ;

如果条件不能使用其他参数，mysqli select语句

3 个答案: