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
原文：http://www.cnblogs.com/-scl/p/7524479.html