sql语句if，case when

Posted 2020-10-07 孟夏草木长

1.if

表达式：IF( expr1 , expr2 , expr3 )

expr1条件，条件为true，则值是expr2 ，false，值就是expr3 

例：

SELECT 
o.id,u.account,catagory.`name`,orderTime,detail.amount,periodtime,if(direction=‘0‘,‘看涨‘,‘看跌‘) directionName
FROM t_order_detail detail
LEFT JOIN t_order o ON o.id = detail.orderId
LEFT JOIN t_catagory catagory ON catagory.id = o.catId
LEFT JOIN t_user u ON u.id = o.userId

2.case when

case 列名

when 条件 then 结果

else 其它结果

end 别名

例：

SELECT 
CASE detail.`status` WHEN ‘0‘ THEN ‘未开仓‘
WHEN ‘1‘ THEN ‘已开仓‘
WHEN ‘2‘ THEN ‘已平仓‘
ELSE ‘取消订单‘ END
status,
CASE o.type WHEN ‘0‘ THEN ‘单期‘
WHEN ‘1‘ THEN ‘多期‘
ELSE ‘策略‘ END 
typeName
FROM t_order_detail detail
LEFT JOIN t_order o ON o.id = detail.orderId