jeremypedersen / sql-for-idiots

SQL syntax for people with bad memories

SQL For Idiots

Exactly what it sounds like. SQL notes for people (like me) who just can't seem to memorize the commands. We'll try to keep commands here ordered from simple to complex.

Section 1: Basic Basics (Create and delete databases and tables, insert records)

Show what databases are available to work with

SHOW DATABASES;

Create a database

CREATE DATABASE big_company;

Show which database is in use

SELECT database();

Select a database

USE big_company;

Show tables in the database

SHOW TABLES;

Create a new table

CREATE TABLE employees (
    employee_id INT,
    name VARCHAR(80),
    role VARCHAR(80)
);

Describe a table (list its fields and datatypes)

DESC employees;

Show the contents of a table

SELECT * FROM employees;

Delete a table

DROP TABLE employees;

Insert a new record into a table

INSERT INTO employees (employee_id, name, role) 
VALUES (0, 'Jeremy', 'Founder');

(Shortcut) insert a new record into a table, where all fields are specified

INSERT INTO employees VALUES (0, 'Jeremy', 'Founder');

Insert mutiple new records into a table

INSERT INTO employees (employee_id, name, role) 
VALUES 
    (1, 'Erica', 'Co-Founder'),
    (2, 'James', 'CFO'),
    (3, 'Leslie', 'CTO');

Create a table with required fields (meaning fields which cannot be NULL

CREATE TABLE students (
    name VARCHAR(80) NOT NULL,
    gpa INT NOT NULL
);

Create a table with required fields and default values for those fields

CREATE TABLE students (
    name VARCHAR(80) NOT NULL DEFAULT 'noname',
    gpa INT NOT NULL DEFAULT 0
);

Insert an empty record (defaults will get filled in)

INSERT INTO students () VALUES ();

Insert a record where only some fields are specified

INSERT INTO students (name) VALUES ('James');

Create a table with a primary key

CREATE TABLE employees (
    employee_id INT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    team_id INT NOT NULL
);

Create a table with a primary key that increments on its own

CREATE TABLE employees (
    employee_id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    team_id INT NOT NULL
);

Insert records into a table with a primary key (identical-looking records can still be differentiated using the primary key)

INSERT INTO employees (name, team_id) 
VALUES 
    ('Bob', 25),
    ('Bob', 25),
    ('Bob', 25);

(Optional) another way to create a primary key which auto-increments

CREATE TABLE employees (
    employee_id INT AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    team_id INT NOT NULL,
    PRIMARY KEY(employee_id)
);

Section 2: Working with data (CRUD operations)

CRUD = Create, Read, Update, Delete

Create

Create a database

CREATE DATABASE big_company;

Create a table

CREATE TABLE employees (
    employee_id INT AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    team_id INT NOT NULL,
    PRIMARY KEY(employee_id)
);

Create a record in a table

INSERT INTO employees (name, team_id) VALUES ('Bob', 25);

Read

Select all items from a table (read)

SELECT * FROM employees;

Select specific columns

SELECT name FROM employees;

Select records that meet a certain condition

SELECT * FROM employees WHERE name = 'Bob';

Note: Just because we are using WHERE with a specific column, doesn't mean we have to SELECT that column. For instance, if I wanted to know which teams had an employee named "Bob", I could do this:

SELECT team_id FROM employees WHERE name = 'Bob' ;

Note: By default, string comparisons are case insensitive in MySQL.

Select records where one column's value matches the value of another column

SELECT * FROM employees where team_id = employee_id;

Rename one or more columns using AS

SELECT employee_id AS id, name FROM employees; 

Update

Update an existing row in a table

UPDATE employees SET name = 'Other Bob' WHERE employee_id = 1;

Update a single column for all rows at once

UPDATE employees SET name = 'Whatever';

Update multiple columns for all rows at once

UPDATE employees SET name = 'Whatever', team_id = 0;

Delete one row

DELETE FROM employees WHERE employee_id = 1;

Delete one or more rows that match a pattern

DELETE FROM employees WHERE name = 'Whatever';

Delete all rows

DELETE FROM employees;

Section 3: Working with string functions

Nothing to see here yet! Getting around to it...