eolas/Databases/SQL/2_SELECT.md

tags
Programming_Languages Databases sql

SQL: The SELECT query

Print/retrieve/write an entire table, unfiltered

SELECT * FROM [table_name]

SELECT * FROM model

Retrieve all data from a specific field

SELECT [field_name] FROM [table_name]

SELECT name FROM manufacturer

Retrieve data and order it

This example orders alphabetically:

SELECT [field_name] FROM [table_name] ORDER BY [property]
SELECT name FROM model ORDER BY name 

When ORDER BY is used the default method for strings is alphabetical and for integers it is ascending order.

Here's a more complex real-life request:

SELECT name, cores, ram FROM model ORDER BY ram, name

It gives us:

name              cores       ram
----------------  ----------  ----------
Commodore VIC-20  1           0.005
Commodore 64      1           0.064
Amiga 500         1           0.5
Apple Lisa        1           1.0
Raspberry Pi 1 M  1           256.0
Raspberry Pi 1 M  1           256.0
Raspberry Pi 1 M  1           512.0
Raspberry Pi 1 M  1           512.0
Raspberry Pi 1 M  1           512.0
Raspberry Pi Zer  1           512.0

But we can obviously specify our own ordering method:

SELECT name, cores, release_date FROM model ORDER BY cores DESC, name;

Returns:

name               cores       release_date
-----------------  ----------  ------------
Apple MacBook Pro  6           2019-05-21
Apple iMac         4           2019-03-19
Raspberry Pi 2 Mo  4           2015-02-01
Raspberry Pi 3 Mo  4           2018-11-01
Raspberry Pi 3 Mo  4           2016-02-01
Raspberry Pi 3 Mo  4           2018-03-14
Raspberry Pi 4 Mo  4           2019-06-24
Raspberry Pi 4 Mo  4           2019-06-24
Raspberry Pi 4 Mo  4           2019-06-24

ORDER BY always comes last, after the selection and any filtering clauses but before a WHERE clause