在项目开发中，我们常常会用到根据不同条件，执行不同的sql,在mysql中可以用 IF(expr1,expr2,expr3) 来满足这个需求。下面我给大家一个示例：
示例1：sql比较复杂
SELECT
if(dom.PLAN_NO is null,
(ifnull( ( SELECT sum( DELIVERY_QTY ) FROM delivery_order_materiel WHERE 1=1 and PO_NO=pom.PO_NO and MATERIEL_CODE = pom.MATERIEL_CODE ), 0 )),
ifnull( ( SELECT sum( DELIVERY_QTY ) FROM delivery_order_materiel WHERE POM_PM_CODE = pom.PM_CODE AND PLAN_NO = dpm.PLAN_NO ), 0 )
)AS tempFiled
from tableName
where 1=1
示例2：
SELECT
if(dom.PLAN_NO=1,
( SELECT sum( DELIVERY_QTY ) FROM delivery_order_materiel WHERE 1=1 and PO_NO=pom.PO_NO and MATERIEL_CODE = pom.MATERIEL_CODE ),
( SELECT sum( DELIVERY_QTY ) FROM delivery_order WHERE 1=1 AND PLAN_NO = dpm.PLAN_NO )
)AS tempFiled
from tableName
where 1=1
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