MySQL查询来计数两列中的所有列值，并在总数中排除NULL值？
让我们首先创建一个表-
mysql> create table DemoTable1975 ( StudentName varchar(20), StudentMarks int );
使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1975 values('John',45);
mysql> insert into DemoTable1975 values('Chris',67);
mysql> insert into DemoTable1975 values('David',59);
mysql> insert into DemoTable1975 values('Bob',NULL);使用select语句显示表中的所有记录-
mysql> select * from DemoTable1975;
这将产生以下输出-
+-------------+--------------+ | StudentName | StudentMarks | +-------------+--------------+ | John | 45 | | Chris | 67 | | David | 59 | | Bob | NULL | +-------------+--------------+ 4 rows in set (0.00 sec)
这是查询以计算所有列值-
mysql> select count(StudentName)+count(StudentMarks) from DemoTable1975;
这将产生以下输出-
+----------------------------------------+ | count(StudentName)+count(StudentMarks) | +----------------------------------------+ | 7 | +----------------------------------------+ 1 row in set (0.00 sec)