在MYSQL中执行左外部联接时插入零而不是NULL
在两个表上执行左外部联接时,是否有方法插入零而不是NULL 假设我有这样一个查询:在MYSQL中执行左外部联接时插入零而不是NULL,mysql,database,Mysql,Database,在两个表上执行左外部联接时,是否有方法插入零而不是NULL 假设我有这样一个查询: SELECT * FROM (SELECT uID from Class) T1 LEFT OUTER JOIN (SELECT pID from University) T2 ON T1.uID = T2.pID CASE WHEN T1.uID IS NULL THEN 0 ELSE T1.uID END AS uID` 如果我错了,请纠正我使用ISNULLfield,0如果字段为NULL,这将插入
SELECT * FROM
(SELECT uID from Class) T1
LEFT OUTER JOIN
(SELECT pID from University) T2
ON T1.uID = T2.pID
CASE WHEN T1.uID IS NULL
THEN 0
ELSE T1.uID
END AS uID`
如果我错了,请纠正我使用ISNULLfield,0如果字段为NULL,这将插入零,类似于:-
CASE WHEN a.fieldname IS NULL
THEN 0
ELSE a.fieldname
END AS fieldname
SELECT * FROM
(SELECT ifnull(uID,0) as uID from Class) T1
LEFT OUTER JOIN
(SELECT ifnull(pID,0) as pID from University) T2
ON T1.uID = T2.pID
选择*从类T1中选择uID左外部联接从大学T2中选择pID在T1.uID=T2.pID的情况下T1.uID为NULL然后选择0其他T1.uID结束为uID如果我错了请更正如果要在T1.uID为NULL时以0的形式联接T1.uID,下面使用:从SELECT CASE中选择*当uID为NULL时,则选择0否则uID结束为类T1中的uID左外部连接从大学T2中选择pID在T1上。uID=T2.pID对于MySQL,您的意思是ifnull而不是isnull=