Better sq lqueries

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Writing Better MySQL Queries for BeginnersDave StokesMySQL Community Manager

[email protected] @stoker


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Agenda

SQL history and offitiesData Storage – why all INTs should not be BIGINT, etc.Table Design Indexes – why to index columns on the right side of a

WHEREQUERY monitoring and optimizationQ/A


SQL

Structured Query Language

Based on relational algebra and tuple relational calculus

Two parts– Data definition language

– Data manipulation language

SELECT name, address

FROM customers

WHERE age > 21 AND state = 'CA';


Cod and Date, er, E.F. Codd C.J. Date


NULL, three-valued logic, and

NULLs are used to show no value but have the side effect of making just about everything from enums to indexes much more difficult to process and optimize. Avoid as much as you can!


Slide to check if audience is awake


Data Types

MySQL has data types for integers, decimals, dates, strings, BLOBS (not binary large object but like 'The Thing that Ate Cincinatti').

Note that character sets can affect size of character data – Latin1 'A' is one char, thee in UTF8


Size matters!

Many programmers use the biggest

Possible data type 'just in case' but it

Wastes space, bandwidth, and time.

Is a Wordpress blog really going to have

9,223,372,936,054,775,807

Entries?!?!?


Select just what you need for SPEED!

Bad:

SELECT *

FROM customers

Better:

SELECT fname, lname, email

FROM customers

Let say you need to spam your customers, query on the left will use the * wild card to return all columns from the customers table. If this table has many columns, there is a lot of extra data movement (disk, memory, network, buffers, etc.) when all you need is three columns.


Third normal form

A memorable statement of Codd's definition of 3NF, paralleling the traditional pledge to give true evidence in a court of law, was given by

Bill Kent: "[Every] non-key [attribute] must provide a fact about the key, the whole key, and nothing but the key."[6] A common variation

supplements this definition with the oath: "so help me Codd".

Kent, William. "A Simple Guide to Five Normal Forms in Relational Database Theory", Communications of the ACM 26 (2), Feb. 1983, pp. 120–125

Diehr, George. Database Management (Scott, Foresman, 1989), p. 331.


Third normal – simplified (probably too much)

Each row has a key and everything else on Each row has a key and everything else on the row is unique to that keythe row is unique to that key– very simplified but a decent guideline


INDEXes

MySQL Manual 8.3.1. How MySQL Uses Indexes

Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. If the table has an index for the columns in question, MySQL can quickly determine the position to seek to in the middle of the data file without having to look at all the data. If a table has 1,000 rows, this is at least 100 times faster than reading sequentially.


Sheeri's Session after this session

Are You Getting the Best Out of Your MySQL Indexes

– Same room

– 11:30 AM


INDEX rough rules

1. Non null, unique, short as possible

2. INDEX columns on right side of WHERE in a query (very, very crude)

3. After #2, go out and really learn indexes!

4. Composite index are your friend

5. Indexes will not help when you have to perform a full table scan

6. Learn how to use EXPLAIN


Monitoring

There are tools to help you gauge efficiency – MySQL Workbench, MySQL Enterprise Monitor, PHPmyAdmin, etc that can give you a clue. But you need a good understanding of query optimization first. But be aware they are there!


Resources

Find Info on MySQL.Com

EMEA contact – [email protected]

North America contact – [email protected]

Planet.MySQL.Com – Best MySQL Blogs

Los Angeles MySQL User Group

'Ping' Lenka or Dave

ForAnything

MySQL UserGroup Related


Virtual Developer Day March 12Virtual Developer Day: MySQL is a one-stop shop for you to learn all the essential MySQL skills. With a combination of presentations and hands-on lab experience, you’ll have the opportunity to practice in your own environment and sharpen your skills to: • Develop your new applications cost-effectively using MySQL • Improve performance of your existing MySQL databases • Manage your MySQL environment more efficiently

https://oracle.6connex.com/portal/mysql/login/?langR=en_US&mcc=launch


Review

1. SQL is odd, get used to it.

2. Use the right size for your data

3. Select what you need for speed

4. Use 3NF

5. Learn indexes, learn to monitor instances


Q&A

Slides at http://slideshare.net/davestokes/presentations



Better sq lqueries

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