sql - 在SQL的多个列中计算不同的值对

Question

哪个查询将计算行数，但由三个参数来区分？

例:

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

就像是:

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

Answer 1

要计算id，name和address的唯一组合的数量:

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