select unique in sql code example
Example 1: select count of distinct values sql
SELECT COUNT (DISTINCT column-name) FROM table-name
Example 2: DISTINCT SQL
SELECT DISTINCT column1, column1, ..... FROM TABLE
Example 3: how to select unique element 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.
Example 4: unique element 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.
Example 5: sql unique
This constraint ensures all values in a column are unique.
Example 1 (MySQL): Adds a unique constraint to the id column when
creating a new users table.
CREATE TABLE users (
id int NOT NULL,
name varchar(255) NOT NULL,
UNIQUE (id)
);
Example 2 (MySQL): Alters an existing column to add a UNIQUE
constraint.
ALTER TABLE users
ADD UNIQUE (id);
Example 6: sql server select rows by distinct column
SELECT a.*
FROM emails a
INNER JOIN
(SELECT email,
MIN(id) as id
FROM emails
GROUP BY email
) AS b
ON a.email = b.email
AND a.id = b.id;