情况下，当MySQL与多个条件

Question

我做了以下情况时声明我的SQL：

SELECT 
*, 
CASE 
    WHEN lead_time < 14 THEN 0 
    WHEN (14 <= lead_time < 21 AND days_passed = 8) THEN 1 
    WHEN 
     (21 <= lead_time < 28 
      AND days_passed = 15) 
    THEN 
     1 
    WHEN 
     (28 <= lead_time < 42 
      AND days_passed = 22) 
    THEN 
     1 
    WHEN 
     (42 <= lead_time < 56 
      AND days_passed = 36) 
    THEN 
     1 
    WHEN 
     (56 <= lead_time < 84 
      AND days_passed = 29) 
    THEN 
     1 
    WHEN 
     (56 <= lead_time < 84 
      AND days_passed = 50) 
    THEN 
     1 
    WHEN (lead_time > 84 AND days_passed = 36) THEN 1 
    WHEN (lead_time > 84 AND days_passed = 57) THEN 1 
    ELSE 0 
END AS send_email 

我没有得到任何错误。然而，当我检查结果我得到：

# lead_time, days_passed, send_email 
99, 15, 1 
99, 22, 1 
99, 15, 1 
99, 8, 1 
99, 8, 1 
99, 8, 1 
99, 8, 1 
85, 29, 1 
57, 50, 1 
18, 36, 1 
99, 22, 1 
99, 22, 1 
99, 22, 1 
99, 22, 1 
99, 22, 1 
15, 15, 1 
15, 15, 1 
99, 8, 1 
99, 8, 1 
99, 8, 1 
99, 8, 1 

它看来，如果“和”在查询表现为一个“或”。任何想法为什么？ 谢谢，

Answer 1

MySQL不支持语法：

min <= expr <= max 

这种类型的表达式可以写为：

WHERE expr >= min AND expr <= max 

或使用运营商之间（请注意，之间包容性）：

WHERE expr BETWEEN min AND max 

MySQL中的比较运算符：http://dev.mysql.com/doc/refman/5.5/en/comparison-operators.html

Answer 2

比较14 <= lead_time < 21 AND days_passed = 8按顺序检查，所以在某种程度上你有：

((14 <= lead_time) < 21) AND (days_passed = 8) 

这始终是true因为14 <= lead_time等于1，所以你的比较是等于：

(1 < 21) AND days_passed = 8 

对于每个比较，您应该使用between或and。