Detailed explanation of how to write mysql not equal to null and equal to null

1. Table structure

2. Table data

3. The query teacher_name field cannot be equal to empty and cannot be equal to the empty character

SELECT * FROM sys_teacher WHERE teacher_name IS NOT NULL AND teacher_name <>''

Query results:

4. Query the teacher_name field to be equal to null or equal to an empty character

SELECT * FROM sys_teacher WHERE teacher_name = '' OR teacher_name IS NULL

Query results:

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