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 vote100 views1 answer
Mysql database is not starting in xampp
SQL
3 votes106 views1 answer
Oracle apex warning message
SQL
0 vote129 views1 answer
Mysql equivalent decode oracle
SQL
1 vote110 views1 answer
Postgresql create table with timestamp
SQL
0 vote111 views1 answer
Mysql a from on this page has
SQL
0 vote117 views1 answer
Alter check command
SQL
1 vote139 views1 answer
Epoch time converter in snowflake
SQL
11 votes290 views4 answers
Round in sql
SQL
0 vote133 views1 answer
How to define a non primary composite key in sql
SQL
0 vote146 views1 answer
Database disk image is malformed sqlite fix ubuntu
SQL