MySQL Basics Workshop

David.Stokes@Oracle.com@stoker

Slideshare.net/DaveStokes

Converge 201416th August

Databases Can Be a Mystery, Misery, or Magnificent

● You do not need to be a DBA

● Nothing wrong with being a DBA● You should think in sets

● 'Relational Calculus for $500, Alex.'● Let the Database do the Heavy Lifting

● Check Return Codes!!!● Select What you need for speed

● Yes, YOU do need to do backups● And know how to restore from them

SQL Structured Query Language

Structured Query Language (/ˈɛs kjuː ˈɛl/,[4] or /ˈsiːkwəl/; (SQL)[5][6][7][8]) is a

special-purpose programming language designed for managing data held in a

relational database management system (RDBMS).

Originally based upon relational algebra and tuple relational calculus, SQL consists of a

data definition language and a data manipulation language. The scope of SQL includes data insert, query,

update and delete, schema creation and modification, and data access control. Although SQL is often

described as, and to a great extent is, a declarative language (4GL), it also includesprocedural elements.

relational algebra is an offshoot of first-order logic and of algebra of sets concerned with operations over

finitary relations, usually made more convenient to work with by identifying the components of a tuple by a

name (called attribute) rather than by a numeric column index, which is called a relation in database

terminology.

--Wikipedia

You send SQL to the server …

The mysqld process will take your input and parse it for VALID syntax.

Then it will build a query plan on how best to retrieve the data.

Finally it goes to fetch the data.

MySQL’s NoSQL queries that skip these steps are MUCH faster – 9 times faster!

GOALs

1. Get the data that you need and only what you need as fast as possible. No ‘SELECT * FROM’

2. Avoid unnecessary disk/memory reads and disk writes.

3. Make data as compact as is useful, no BIGINTs for age.

18,446,744,073,709,551,615 is pretty old!

Integers

Type Storage (bytes)

Minimum Signed

Maximum Signed

Minimum Unsigned

Maximum Unsigned

TINYINT 1 -128 127 0 255

SMALLINT 2 -32768 32768 0 65535

MEDIUMINT

3 -8388608 8388607 0 16777215

INT 4 -2147483648 2147483647 0 4294967295

BIGINT 8 -9223372036854

775808

9223372036854775807

0 18446744073709551615

Are you really going to have 18,446,744,073,709,551,615 customer id numbers?

Cost Based Optimizer

C.5.6. Optimizer-Related Issues

MySQL uses a cost-based optimizer to determine the best way to resolve a query. In many cases, MySQL can

calculate the best possible query plan, but sometimes MySQL does not have enough information about the

data at hand and has to make “educated” guesses about the data.

So MySQL wants to get your data as cheaply as possible and plans accordingly.

Query Plan not lockable with MySQL

Each time MySQL gets a query it will optimize it!

It builds a list of statistics over time to help keep track of data & speed retrieval of the data (5.6 lets you save/restore this information)

Clue: You want FAST!

EXPLAIN

EXPLAIN is a tool to ask the server how it wants to optimize the query.

Prepend to a QUERY

Example Table

Example Query

Example EXPLAIN

Example EXPLAIN with \G

Read ALL rows in table

A Quick Word on Indexes

Indexes allow you to go directly to the record(s) you want (think SSN) instead of reading all records to find the one(s) wanted.

But they require maintenance and overhead.

Not a panacea!

What the heck is a B-Tree?!??!?!

Using WHERE

274 Records Read!

Previous query w/o INDEX

No index used and all records in table readto find 274 records

How to find index(es) already in use

OR ...

\G forVertical

A more common example

Optimizer estimates 8 reads to get desired info

Could use the PRIMARY key but does not!!

Has to read all records

239 x 8 = 1,912 records to read

Slightly more complex query

SELECT a.Name as 'City',

b.Name as 'Country',

a.population

FROM City a

JOIN Country b

ON (a.CountryCode = b.Code)

WHERE a.population > 3000000

AND b.LifeExpectancy > 66

ORDER BY b.name, a.Population

LIMIT 20;

Gee, we add all those qualifiersand it still has to readAll those records AND we get a temp table plus a file sort!

And we ONLY wanted 20 records!!!

Visual Explain

MySQL 5.6 and

Workbench 6.1 use

JSON format output

to generate diagram.

Costs published with

5.7 and 6.1!

Yet a little deeper into complexitySELECT CONCAT(customer.last_name, ', ', customer.first_name) AS customer,

address.phone, film.title

FROM rental INNER JOIN customer ON rental.customer_id = customer.customer_id

INNER JOIN address ON customer.address_id = address.address_id

INNER JOIN inventory ON rental.inventory_id = inventory.inventory_id

INNER JOIN film ON inventory.film_id = film.film_id

WHERE rental.return_date IS NULL

AND rental_date + INTERVAL film.rental_duration DAY < CURRENT_DATE()

LIMIT 5;

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A little easier to understand

Compound Indexes

We can use this index searching on

1. City, State, and Zip

2. City, State

3. City

Covering Indexes

ALTER TABLE city ADD INDEX country_idx (CountryCode, Population);

The INDEX contains all the data we are searching for which means less data to look-up,

one less read into the data

Musts for better queries

1. Read chapter 8 of the MySQL Manual

2. Join on like data types, INTs with INTS

3. Keep columns as small as practical (PROCEDURE ANALYSE)

4. Maintain B-tree index with ANALYSE TABLE when things are quiet

5. Keep looking for improvments

Check Return Codes (please)<?php$link = mysqli_connect("localhost", "my_user", "my_password", "world");

/* check connection */if (mysqli_connect_errno()) { printf("Connect failed: %s\n", mysqli_connect_error()); exit();}

if (!mysqli_query($link, "SET a=1")) { printf("Errorcode: %d\n", mysqli_errno($link));}

Hard to teach all in a few minutes

MySQL Central @ Oracle Open WorldMySQL Central @ Oracle Open World

Five days with the MySQL Engineers, innovative customers (Facebook, Twitter, Playful Play, Booking, DropBox, Paypal, & you), and the top professionals from the MySQL Community.

Starts September 28th in San Francisco!

Questions and Answers

David.Stokes@Oracle.com

@stoker

Slideshare.net/davestokes