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 vote325 views1 answer
Tsql default value when no value returned by query
SQL
0 vote313 views1 answer
Restart postgresql.service Failed to restart postgresql.service: Unit not found.
SQL
-1 vote362 views3 answers
Error: mysql shutdown unexpectedly.
SQL
2 votes353 views6 answers
Mysql change timezone
SQL
1 vote343 views1 answer
Mysql check if string contains comma separated
SQL
7 votes330 views1 answer
Sql server convert string to date
SQL
2 votes327 views1 answer
Node and mysql like
SQL
5 votes337 views1 answer
Oracle list functions
SQL
4 votes391 views1 answer
Fatal error: libpq-fe.h: No such file or directory
SQL
1 vote341 views1 answer
Woocommerce mysql price table
SQL