php - 尝试在 CASE WHEN mysql php 中使用 CASE WHEN ？

Question

看看我的代码，我想实现类似的效果，当 cat='1' 时，然后 CASE 或当 cat='2' 时，然后 CASE。帮忙，感激不尽。

<?php
$test ="SELECT DISTINCT dis from $table WHERE 
              ( 
              CASE When cat='1' THEN (CASE  
                      WHEN val2 ='g' THEN val1 > %d
		      WHEN val2 ='l' THEN val1 < %d
		      ELSE val1 !=%d END) 
     
               When cat='2' THEN (CASE  
                      WHEN val2 ='g' THEN val1 > %d
		      WHEN val2 ='l' THEN val1 < %d
		      ELSE val1 !=%d END)
              ELSE END
               )
			   AND dis IN ('19','20','21')
			   ";
?>

Answer 1

在一个 CASE 语句中尝试一下，看看它是否返回预期的结果:

<?php
$test ="SELECT DISTINCT dis from $table 
WHERE CASE 
WHEN cat='1' AND val2 ='g' THEN val1 > %d
WHEN cat='1' AND val2 ='l' THEN val1 < %d
WHEN cat='1' THEN val1 !=%d
WHEN cat='2' AND val2 ='g' THEN val1 > %d
WHEN cat='2' AND val2 ='l' THEN val1 < %d
WHEN cat='2' THEN val1 !=%d
END
AND dis IN ('19','20','21')
";
?>

此外，根据 cat = 1 或 2 的不同，看起来没有任何差异，因此您可以将 CASE 减少为:

CASE 
WHEN cat in ('1','2') AND val2 ='g' THEN val1 > %d
WHEN cat in ('1','2') AND val2 ='l' THEN val1 < %d
WHEN cat in ('1','2') THEN val1 !=%d
END