如果所有行都不为空,则总和在 MySQL 中返回空值?
您可以在GROUPBYHAVING子句的帮助下实现这一点。语法如下-
SELECT yourColumnName1, SUM(yourCoumnName2) from yourTableName GROUP BY yourColumnName1 HAVING COUNT(yourCoumnName2) = COUNT(*);
为了理解上述语法,让我们创建一个表。创建表的查询如下-
mysql> create table SumDemo -> ( -> Id int, -> Amount int -> );
使用插入命令在表中插入一些记录。查询如下-
mysql> insert into SumDemo values(1,200); mysql> insert into SumDemo values(2,100); mysql> insert into SumDemo values(2,NULL); mysql> insert into SumDemo values(1,300); mysql> insert into SumDemo values(2,100); mysql> insert into SumDemo values(1,500);
使用select语句显示表中的所有记录。查询如下-
mysql> select *from SumDemo;输出结果
+------+--------+ | Id | Amount | +------+--------+ | 1 | 200 | | 2 | 100 | | 2 | NULL | | 1 | 300 | | 2 | 100 | | 1 | 500 | +------+--------+ 6 rows in set (0.00 sec)
如果所有行都不为空,则这是获取总和的查询,否则返回空值。查询如下-
mysql> select Id, -> SUM(Amount) -> from SumDemo -> GROUP BY ID -> HAVING COUNT(Amount) = COUNT(*);
以下是输出。由于id2为NULL,因此不会将其值添加到总和中。
因此,将添加Id1的所有值,即200+300+500=1000,如下所示-
+------+-------------+ | Id | SUM(Amount) | +------+-------------+ | 1 | 1000 | +------+-------------+ 1 row in set (0.09 sec)