SQL运算符
//不为空
SELECT * FROM `table_name` WHERE 'col'<>''
//为空
SELECT * FROM `table_name` WHERE 'col'=''
SQL命令
//不为空
SELECT * FROM `table_name` WHERE 'col IS NOT NULL
//为空
SELECT * FROM `table_name` WHERE 'col IS NULL
//不为空
SELECT * FROM `table_name` WHERE 'col'<>''
//为空
SELECT * FROM `table_name` WHERE 'col'=''
//不为空
SELECT * FROM `table_name` WHERE 'col IS NOT NULL
//为空
SELECT * FROM `table_name` WHERE 'col IS NULL