1.表结构 2.表数据 3.查询teacher_name字段不能等于空并且也不能等于空字符 SELECT * FROM sys_teacher WHERE teacher_name IS NOT NULL AND teacher_name '' 查询结果： 4.查询teacher_name字段等于null或等于空字符
1.表结构
2.表数据
3.查询teacher_name字段不能等于空并且也不能等于空字符
SELECT * FROM sys_teacher WHERE teacher_name IS NOT NULL AND teacher_name <>''
查询结果：
4.查询teacher_name字段等于null或等于空字符
SELECT * FROM sys_teacher WHERE teacher_name = '' OR teacher_name IS NULL
查询结果：
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