is null && is not null
2017-12-21 18:10
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1.在 MySQL 中,NULL 值与任何其它值的比较(即使是 NULL)永远返回 false,即 NULL = NULL 返回false 。
2.MySQL 中处理 NULL 使用 IS NULL 和 IS NOT NULL 运算符。
select c.company_id ,c.`name`,i.amount from tb_company_lang as c join tb_investor as i on c.company_id=i.company_id and i.amount is not null
3.<=>: 比较操作符(不同于=运算符),当比较的的两个值为 NULL 时返回 true。
select c.company_id ,c.`name`,i.amount from tb_company_lang as c join tb_investor as i on c.company_id=i.company_id and i.amount <=> null
这里的<=> null效果等同于 is null
2.MySQL 中处理 NULL 使用 IS NULL 和 IS NOT NULL 运算符。
select c.company_id ,c.`name`,i.amount from tb_company_lang as c join tb_investor as i on c.company_id=i.company_id and i.amount is not null
3.<=>: 比较操作符(不同于=运算符),当比较的的两个值为 NULL 时返回 true。
select c.company_id ,c.`name`,i.amount from tb_company_lang as c join tb_investor as i on c.company_id=i.company_id and i.amount <=> null
这里的<=> null效果等同于 is null
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