1.if

表達式：IF( expr1 , expr2 , expr3 )

expr1條件，條件為true，則值是expr2 ，false，值就是expr3

例：

SELECT 
o.id,u.account,catagory.`name`,orderTime,detail.amount,periodtime,if(direction=‘0‘,‘看漲‘,‘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 條件 then 結果

else 其它結果

end 別名

例：

SELECT 
CASE detail.`status` WHEN ‘0‘ THEN ‘未開倉‘
WHEN ‘1‘ THEN ‘已開倉‘
WHEN ‘2‘ THEN ‘已平倉‘
ELSE ‘取消訂單‘ END
status,
CASE o.type WHEN ‘0‘ THEN ‘單期‘
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

sql語句if，case when