1. 修改字段為NULL
update tableName set column1 = null where id = 1
2. 字段是否為NULL
(1)字段為空
select * tableName where column1 is null
(2)字段不為空
select * tableName where column1 is not null
1. 修改字段為NULL
update tableName set column1 = null where id = 1
2. 字段是否為NULL
(1)字段為空
select * tableName where column1 is null
(2)字段不為空
select * tableName where column1 is not null
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