lk/data/sql/sql.md
2020-01-02 01:04:35 +01:00

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MySQL, Aurora and the Maria Database work similarly, and mostly with the same commands.
MySQL requires 160 Megs of disk space.
The ontological layers go:
> Database > table > record > field
The record is a line containing multiple fields. The table contains multiple records.
## Database: RPGs
### Table: D&D
#### Columns:
| id | name | year | edition | stars |
|:--:|:-------------------|:-----|:--------|:------|
| 1 | Dungeons & Dragons | 1975 | 1 | 1 |
| 2 | Dungeons & Dragons | 1980 | 2 | 1 |
| 3 | Advanced Dungeons & Dragons | 1985 | 1 | 1 |
# Getting started
> sudo apt-get install mysql-server
You'll be asked for a password.
Log in with:
> mysql -u root -p
The -u requests a user, while -p tells it to prompt for a password.
List all databases:
> show databases;
Make a new database;
> create database creatures;
Start work on the new database:
> use creatures;
> create table stats (Strength VARCHAR(2), Speed VARCHAR(2), Dexterity(2));
This creatures a row called 'stats' within the 'creature'table' with a number of variables, all of type VARCHAR (a variable length character string).
Now you can insert data (which would normally be provided by a user via php or some-such).
> insert into stats (Strength,Speed,Dexterity) values (-1,0,+1)
Now have a look at the info:
> select * from stats
The old way to delete info by selection was:
> delete * from stats where Charisma='0'
...but now it's:
> delete from stats where Charisma='0'
Update a thing:
> update stats
> set Speed='-1',Charisma='-2'
> where Strength=0;
Leaving out the specifier 'where' means you're updating the entire database.
Control order with
> SELECT * FROM stats ORDER BY Strength;
Or for descending order, suffix 'DESC'.
> select * from stats ORDER by Date DESC;
# Resources
Try more at [w3schools](http://www.w3schools.com/sql/sql_groupby.asp).