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.

SELECT

DISTINCT country

FROM City;

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.

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.

SELECT DISTINCT col1, col2, ....

FROM table_name;

​

SELECT col1, MIN(col2)

FROM table_name

GROUP BY col1;

CREATE TABLE order_details

( order_detail_id integer CONSTRAINT order_details_pk PRIMARY KEY,

  order_id integer NOT NULL,

  order_date date,

  quantity integer,

  notes varchar(200),

  CONSTRAINT order_unique UNIQUE (order_id)

);

CREATE TABLE Persons (

    ID int NOT NULL UNIQUE,

    LastName varchar(255) NOT NULL,

    FirstName varchar(255),

    Age int

);