mysql的update之where条件判断null

update 表名 set belongSysCode = 'DSJJQ' where useFor = '测试' and belongSysCode ='' OR belongSysCode = ''; #执行失败

上边的语句执行不会报错,但是也没有成功
将 where 条件中的改为:
belongSysCode is null,执行成功

update assets_host set belongSysCode = 'DSJJQ' **where** useFor = '测试' and **belongSysCode IS NULL** OR belongSysCode = '' ;  #执行成功

另外注意:
set 之后 where 之前的部分,想要将某个字段设置为null ,必须用 字段 = null

update assets_host set belongSysCode = 'null' where useFor = '测试' and belongSysCode = 'DSJJQ' OR belongSysCode = ''; #执行成功
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