📜  如何在sql代码示例中找到唯一元素

📅  最后修改于: 2022-03-11 15:05:08.304000             🧑  作者: Mango

代码示例1
DISTINCT
- select distinct * from employees; ==> 
           retrieves any row if it has at 
           least a single unique column.
- select distinct first_name from employees; ==> 
              retrieves unique names
              from table. (removes duplicates)
- select distinct count(*) from employees;
          retrieve number of unique rows
          if any row has at least a single unique data.