SQL運算符
//不為空
SELECT * FROM `table_name` WHERE 'col'<>''
//為空
SELECT * FROM `table_name` WHERE 'col'=''
SQL命令
//不為空
SELECT * FROM `table_name` WHERE 'col IS NOT NULL
//為空
SELECT * FROM `table_name` WHERE 'col IS NULL
//不為空
SELECT * FROM `table_name` WHERE 'col'<>''
//為空
SELECT * FROM `table_name` WHERE 'col'=''
//不為空
SELECT * FROM `table_name` WHERE 'col IS NOT NULL
//為空
SELECT * FROM `table_name` WHERE 'col IS NULL
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