Question

我有一个包含两列的表格，如下所示：

name         marks
  A            15
  B            
  c            20

从上方可以清楚地看到，列name具有3个非空值和1个空值，同样，列marks具有2个空值和2个非空值。

要获得此结果的查询是什么？

Answer 1

您可以执行此操作-

SELECT COUNT(name) AS name_not_null_count, 
       SUM(CASE WHEN name IS NULL THEN 1 ELSE 0 END) AS name_null_count
FROM table

计算空计数的方法是：将所有空记录标记为1并取SUM。

Answer 2

SELECT COUNT(name) AS name_count, COUNT(marks) AS marks_count FROM table;

Answer 3

count(columnname)仅计算非空值。 count(*)计算所有行。

select count(name) as names,
       count(*) - count(name) as null_names,
       count(marks) as marks,
       count(*) - count(marks) as null_marks
from tablenam

Answer 4

这将选择行数，具有空值的行数和具有非空值的行数。对每个所需的列重复选择。

MOVMSKB

Num_Rows Num_Not_Null Num_Null

4 3 1

计算表中所有列的空值和非空值

4 个答案: