SQL用于查找列中不同值的数量

Question

我可以通过以下方式选择列中的所有不同值:

• SELECT DISTINCT column_name FROM table_name;
• SELECT column_name FROM table_name GROUP BY column_name;

但是如何从该查询中获取行数呢？是否需要子查询？

Answer 1

您可以DISTINCT在COUNT聚合函数中使用关键字:

SELECT COUNT(DISTINCT column_name) AS some_alias FROM table_name

这将仅计算该列的不同值.

Answer 2

这将为您提供不同的列值和每个值的计数.我经常发现我想知道这两条信息.

SELECT [columnName], count([columnName]) AS CountOf
FROM [tableName]
GROUP BY [columnName]

Answer 3

请注意Count()忽略空值,因此如果您需要允许null作为其自己的不同值,您可以执行一些棘手的操作:

select count(distinct my_col)
       + count(distinct Case when my_col is null then 1 else null end)
from my_table
/

Answer 4

column_name的唯一值的sql总和并按频率排序:

SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name ORDER BY 2 DESC;

Answer 5

select count(*) from 
(
SELECT distinct column1,column2,column3,column4 FROM abcd
) T

这将给出不同组列的计数.

Answer 6

SELECT COUNT(DISTINCT column_name) FROM table as column_name_count;

你必须计算那个不同的col,然后给它一个别名.

Answer 7

select Count(distinct columnName) as columnNameCount from tableName