SQL Cheat Sheet

Statements

 

AS

Used to assign an alias name to a column or a table. Alias is temporary, it exists only during the execution of the query.

 

select CustomerName as customer from customers;

 

AS is optional but is recommended to use it explicitly. So this query is also valid:

select CustomerName customer from customers;

SQL alias: Make Your Query Shorter And More Understandable

SQL AS

SQL Aliases

DROP

Deletes an object (database, table, index or view)

 

DROP (Wikipedia)

 

To drop a database:

 

> drop database northwind;

 

MySQL example how to verify that e.g. database was dropped: 

> show databases;

or 

> select schema_name from information_schema.schemata;

SELECT 

To return all unique last names:

 

SELECT DISTINCT LastName FROM Employees;

Select (SQL) - Wikipedia

Clauses

ORDER BY

 

To sort the output by the LastName field, then by the FirstName field if LastName matches:
 

SELECT * FROM Employees ORDER BY LastName, FirstName;

Order by - Wikipedia

 

JOIN 

 

...

 

https://www.db-fiddle.com/f/tPUgzPgpCwo1qKF9HUFn2v/0

CREATE TABLE Persons_dev (

    PersonID int,

      Name varchar(255)

);

CREATE TABLE Persons_beta (

    PersonID int,

      Name varchar(255)

);

INSERT INTO Persons_dev (PersonID, Name) VALUES (1,'Ana');

INSERT INTO Persons_dev (PersonID, Name) VALUES (2,'Bojan');

INSERT INTO Persons_dev (PersonID, Name) VALUES (3,'Ceca');

INSERT INTO Persons_dev (PersonID, Name) VALUES (4,'Dejan');

INSERT INTO Persons_dev (PersonID, Name) VALUES (5,'Erik');

INSERT INTO Persons_dev (PersonID, Name) VALUES (6,'Florian');

INSERT INTO Persons_beta (PersonID, Name) VALUES (0,'Zero');

INSERT INTO Persons_beta (PersonID, Name) VALUES (1,'Ana');

INSERT INTO Persons_beta (PersonID, Name) VALUES (2,'Bojan');

INSERT INTO Persons_beta (PersonID, Name) VALUES (3,'Ceca');

INSERT INTO Persons_beta (PersonID, Name) VALUES (4,'Deki');

INSERT INTO Persons_beta (PersonID, Name) VALUES (5,'Erik');

SELECT * FROM Persons_dev

WHERE PersonID NOT IN (SELECT PersonID FROM Persons_beta)

UNION 

SELECT * FROM Persons_beta

WHERE PersonID NOT IN (SELECT PersonID FROM Persons_dev)

SELECT Persons_dev.PersonID, Persons_dev.Name, Persons_beta.Name FROM Persons_dev 

INNER JOIN Persons_beta ON Persons_dev.PersonID=Persons_beta.PersonID

WHERE Persons_dev.Name != Persons_beta.Name;

https://www.db-fiddle.com/f/tPUgzPgpCwo1qKF9HUFn2v/3

 

Join (SQL) - Wikipedia

Operators

[NOT] IN

To return all published posts that are present in posts_dev table but not in posts_beta (id is the key):

SELECT * 

FROM posts_dev
WHERE post_status='publish' AND 

              id NOT IN (SELECT ID FROM posts_beta WHERE post_status='publish')

 

Comments

Comments (e.g. in .sql files) are:

 

-- This is a comment in one line

or 

/* This is a comment in one line */

or 

/* 

This is 

a comment 

in multiple lines 

*/

References:

SQL syntax - Wikipedia