How to find unique key in sql

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.

Similar codes

0 vote205 views1 answer
Truncate a table then insert data
SQL
-1 vote199 views1 answer
Mysql faster insert
SQL
10 votes169 views2 answers
Sql rtrim
SQL
0 vote180 views1 answer
How to create a new db from dumb file mysql
SQL
1 vote151 views1 answer
Mysql login console
SQL
1 vote174 views1 answer
Postgres start database on linux
SQL
1 vote165 views1 answer
Apex ORA-20999
SQL
50 votes247 views4 answers
Sql alter type of column
SQL
0 vote170 views1 answer
Sqlcmd xml output insert line break after every 2033 characters
SQL
0 vote163 views1 answer
Postgres enumerated type
SQL