May
25
2010
Episode 70: Know Your Joins
Podcast: Play in new window | Download
How well do you know your database joins? This episode we talk about the different kinds to help make you a join master.
News and Follow-ups – 00:48
- Mark’s tinfoil hack failed
Geek Tool – 03:28
Webapps – 09:48
- Penzu – Online private journal
- Support Details – Online provider of simple support data
Topic – 18:25
- Combines records from two or more tables in a database
- A general rule of thumb is that database joins are faster than doing separate select statements in code.
- Ansi Standard lists 4 types:
- Inner
- Join tables based on a common column Eg. PK/FK
- Most common type of join
- Outer
- Combine all rows of one table with only matching rows on the other table
- Left
- Return all rows on the left table even if not in the right
- Right
- Return all rows in the right table even if not in the left
- Cross join
- Takes two tables and combines every row in table b with every row in table a.
- 1000 row table would produce 1 million rows
- Why make one then?
- Suppose you want a grid of articles of clothing
- select size, color from sizes cross join colors
- MySQL University
- A visual explanation of sql joins
