📜  sql代码示例中的唯一元素

📅  最后修改于: 2022-03-11 15:05:16.707000             🧑  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.