mysql ifelse流程控制语句

mysql ifelse流程控制语句

1. 简单判断
   当 status=1时返回1，否则0 :

   select id, if(status=1, 1, 0) as source from table_1
   

   IF(表达式1, 表达式2 ,表达式3)
   如果表达式1为true（表达式1 <> 0 and 表达式1 <> NULL), 返回表达式2；否则返回表达式3；相当于三目运算符

   mysql> SELECT IF(1>2,2,3);
       -> 3
   mysql> SELECT IF(1<2,'yes','no');
       -> 'yes'
   

2. 多条件语句

select id, 
    (
    CASE 
        WHEN qty_1 <= '23' THEN price
        WHEN '23' > qty_1 && qty_2 <= '23' THEN price_2
        WHEN '23' > qty_2 && qty_3 <= '23' THEN price_3
        WHEN '23' > qty_3 THEN price_4
        ELSE 1
     END
     )  AS total
 from product;