Better sq lqueries

Writing Better
MySQL Queries for
Beginners
Dave Stokes
MySQL Community Manager

David.Stokes@Oracle.com @stoker

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Agenda

 SQL history and offities
 Data Storage – why all INTs should not be BIGINT, etc.
 Table Design
 Indexes – why to index columns on the right side of a
WHERE
 QUERY monitoring and optimization
 Q/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: Better:
SELECT * SELECT fname, lname, email
FROM customers 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
the 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
'Ping' Lenka
or Dave
For
Anything
 Find Info on MySQL.Com MySQL User
Group Related
 EMEA contact – lenka.kasparova@oracle.com

 North America contact – david.stokes@oracle.com

 Planet.MySQL.Com – Best MySQL Blogs

 Los Angeles MySQL User Group


Virtual Developer Day March 12
Virtual 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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