【Mybatis】Mybatis中IFNULL(P1,P2)函式的用法;
阿新 • • 發佈:2019-02-19
1.問題:
Mybatis中IFNULL(p1,p2)函式怎麼用?
首先看沒有IFNULL的查詢:
2.1原始碼:
select md.valueofdouble, md.periodcode
from meas_data md
WHERE objectcode="YQ"
AND datatime="2017-5-25 00:00:00"
AND measurementcode="PI_DRFDL"
2.2.截圖:
3.1原始碼:
select md.valueofdouble, IFNULL(md.periodcode,0)
from meas_data md
WHERE objectcode="YQ"
AND datatime="2017-5-25 00:00:00"
AND measurementcode="PI_DRFDL"
3.2截圖:
4.總結:
1、IFNULL(P1,P2)如果如果P1不為空,則返回值為P1;P1為NULL,則返回為P2;P2有點類似替補球員;
2、注意,IFNULL只是針對區域性欄位的替換;如果整個結果查出來都是空,則不能使用IFNULL(P1,P2)
4.1原始碼:
select md.valueofdouble, md.periodcode
from meas_data md
WHERE objectcode="YQ"
AND datatime="2017-5-25 00:00:01"
AND measurementcode="PI_DRFDL"
4.2截圖:
4.3原始碼:
select md.valueofdouble, IFNULL(md.periodcode,0)
from meas_data md
WHERE objectcode="YQ"
AND datatime="2017-5-25 00:00:01"
AND measurementcode="PI_DRFDL"