计算 SQL 中多列中的不同值对

Question

What query will count the number of rows, but distinct by three parameters?

Example:

Id      Name        Address 
==============================
1     MyName        MyAddress
2     MySecondName  Address2

Something like:

select count(distinct id,name,address) from mytable

Answer 1

To get a count of the number of unique combinations of id , name and address :

SELECT Count(*)
FROM   (
        SELECT DISTINCT
               id
             , name
             , address
        FROM   your_table
       ) As distinctified

Answer 2

获取所有不同的id 、 name和address列并计算结果行。

SELECT COUNT(*) FROM mytable GROUP BY id, name, address

Answer 3

我刚刚想出的另一种（可能不是生产就绪或推荐的）方法是将值连接到一个字符串并特别地计算这个字符串：

SELECT count(DISTINCT concat(id, name, address)) FROM mytable;

Answer 4

您还可以执行以下操作：

SELECT COUNT(DISTINCT id + name + address) FROM mytable

Answer 5

Having to return the count of a unique Bill of Materials (BOM) where each BOM have multiple positions, I dd something like this:

select t_item, t_pono, count(distinct ltrim(rtrim(t_item)) + cast(t_pono as varchar(3))) as [BOM Pono Count]
from BOMMaster
where t_pono = 1
group by t_item, t_pono

Given t_pono is a smallint datatype and t_item is a varchar(16) datatype