10 SQL tips speed database CatsWhoCode

10 sql tips to speed up your database | CatsWhoCode.com

10 sql tips to speed
up your database
On most websites, content is stored in a
database and served to visitors upon
request. Databases are very fast, but there’s
lots of things that you can do to enhance its
speed and make sure you won’t waste any
server resources. In this article, I have
compiled 10 very useful tips to optimize and
speed up your website database.

Design your database
with caution
This first tip may seems obvious, but the fact
is that most database problems come from
badly-designed table structure.
For example, I have seen people storing
information such as client info and payment
info in the same database column. For both
the database system and developers who
will have to work on it, this is not a good
thing.
When creating a database, always put
information on various tables, use clear
naming standards and make use of primary
keys.
Source: http://www.simple-
talk.com/sql/database-
administration/ten-common-
database-design-mistakes/

Know what you
should optimize
If you want to optimize a specific query, it is
extremely useful to be able to get an in-
depth look at the result of a query. Using the
EXPLAIN statement, you will get lots of
useful info on the result produced by a
specific query, as shown in the example

http://www.catswhocode.com/blog/10-sql-tips-to-speed-up-your-database[08/29/2012 11:38:07 AM]


below:

EXPLAIN SELECT * FROM
ref_table,other_table WHERE
ref_table.key_column=other_table.co
lumn;

Source:
http://dev.mysql.com/doc/refman/5.0/e
explain.html

The fastest query… Is
the one you don’t
send
Each time you’re sending a query to the
database, you’re using a bit of your server
resources. This is why, on high traffic sites,
the best thing you can do in order to speed
up your database is to cache queries.

There’s lots of solutions to implement a
query cache on your server. Here are a few:

AdoDB: AdoDB is a database
abstraction library for PHP. It allows you
to use the database system of your
choice (MySQL, PostGreSQL, Interbase,
and way much more) and it is designed
for speed. AdoDB provides a simple,
yet powerful caching system. And last
but not least, AdoDB is licenced under
the BSD, which means that you can use
freely on your projects. A LGPL licence
is also available for commercial
projects.
Memcached: Memcached is a
distributed memory caching system
which is often used to speed up
dynamic database-driven websites by
alleviating database load.
CSQL Cache: CSQL Cache is an
open-source data caching infrastructure.
Never tested it personally, but it seems
to be a great tool.



Don’t select what you
don’t need
A very common way to get the desired data
is to use the * symbol, which will get all
fields from the desired table:

SELECT * FROM wp_posts;

Instead, you should definitely select only the
desired fields as shown in the example
below. On a very small site with, let’s say,
one visitor per minute, that wouldn’t make a
difference. But on a site such as Cats Who
Code, it saves a lot of work for the
database.

SELECT title, excerpt, author FROM
wp_posts;

Use LIMIT
It’s very common that you need to get only a
specific number of records from your
database. For example, a blog which is
showing ten entries per page. In that case,
you should definitely use the LIMIT
parameter, which only selects the desired
number of records.
Without LIMIT, if your table has 100,000
different records, you’ll extract them all,
which is unnecessary work for your server.

SELECT title, excerpt, author FROM
wp_posts LIMIT 10;

Avoid queries in
loops
When using SQL along with a programming
language such as PHP, it can be tempting to
use SQL queries inside a loop. But doing so



is like hammering your database with
queries.
This example illustrates the whole “queries
in loops” problem:

foreach ($display_order as $id =>
$ordinal) {
$sql = "UPDATE categories SET
display_order = $ordinal WHERE id
= $id";
mysql_query($sql);
}

Here is what you should do instead:

UPDATE categories
SET display_order = CASE id
WHEN 1 THEN 3
WHEN 2 THEN 4
WHEN 3 THEN 5
END
WHERE id IN (1,2,3)

Source:
http://www.karlrixon.co.uk/articles/sq
multiple-rows-with-different-values-
and-a-single-sql-query/

Use join instead of
subqueries
As a programmer, subqueries are something
that you can be tempted to use and abuse.
Subqueries, as show below, can be very
useful:

SELECT a.id,
(SELECT MAX(created)
FROM posts
WHERE author_id = a.id)
AS latest_post FROM authors a

Although subqueries are useful, they often
can be replaced by a join, which is definitely



faster to execute.

SELECT a.id, MAX(p.created) AS
latest_post
FROM authors a
INNER JOIN posts p
ON (a.id = p.author_id)
GROUP BY a.id

Source: http://20bits.com/articles/10-
tips-for-optimizing-mysql-queries-
that-dont-suck/

Be careful when using
wildcards
Wildcards are very useful because they can
substitute for one or more characters when
searching for data in a database. I’m not
saying that you shouldn’t use them, but
instead, you should use them with caution
and not use the full wildcard when the prefix
or postfix wildcard can do the same job.
In fact, doing a full wildcard search on a
million records will certainly kill your
database.

#Full wildcard
SELECT * FROM TABLE WHERE COLUMN
LIKE '%hello%';
#Postfix wildcard
LIKE 'hello%';
#Prefix wildcard
LIKE '%hello';

Source: http://hungred.com/useful-
information/ways-optimize-sql-
queries/

Use UNION instead of
OR
The following example use the OR
statement to get the result:



SELECT * FROM a, b WHERE a.p = b.q
or a.x = b.y;

The UNION statement allows you to
combine the result sets of 2 or more select
queries. The following example will return
the same result that the above query gets,
but it will be faster:

SELECT * FROM a, b WHERE a.p = b.q
UNION
SELECT * FROM a, b WHERE a.x = b.y

Source:
http://www.bcarter.com/optimsql.htm

Use indexes
Database indexes are similar to those you
can find in libraries: They allow the database
to find the requested information faster, just
like a library index will allow a reader to find
what they’re looking for without loosing time.
An Index can be created on a single column
or a combination of columns in a database
table. A table index is a database structure
that arranges the values of one or more
columns in a database table in specific
order.

The following query will create an index on
the Model column from the Product table.
The index is called idxModel:

CREATE INDEX idxModel ON Product
(Model);

Source: http://www.sql-
tutorial.com/sql-indexes-sql-tutorial/

More posts about SQL



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Comments (54) - Leave
yours
Bart Jacobs said: March 8,
2010 at 11:49 am
This article is very useful for
anyone working with mySQL
(and with databases in
general). For high traffic
websites especially, database
queries can be the bottleneck
(and often are). Thanks for
this great post!

Reply

Can Aydoğan said: March
8, 2010 at 1:27 pm
Great article. Thanks for
sharing!

Reply



Metric Stormtrooper said:
March 8, 2010 at 3:27
pm
your table type can also make
a lot of difference. MyISAM is
better if you expect a lot of
reads, InnoDB if you need
more writes in a table (see
also
http://www.softwareprojects.com
mysql-storage-engines-
1470.html ).

And don’t forget to enable the
query cache in your my.ini

Reply

Kovica said: March 8, 2010
at 3:29 pm
“Use Indexes” should be #1.

Reply

Jean-
Baptiste
Jung said:
March 9,
2010 at
4:20 am
Tips are
displayed
without
importance
order, but I
agree that
indexes are
definitely
one of the
best way to
optimize
your DB!

Reply



wxianfeng said: March 8,
2010 at 8:57 pm
very helpful~!

Reply

10 sql tips to speed up your
database | [codepotato]
said: March 9, 2010 at
4:00 am
[...] 10 sql tips to speed up
your database Posted March
9th, 2010 in Blog by Gareth
http://www.catswhocode.com/blo
sql-tips-to-speed-up-your-
database [...]

Reply

Anonymous said: March 9,
2010 at 8:13 am
One thing anyone thinking
about optimising their queries
should bear in mind is not to
do it straight away. Get your
code working and then go
back to it and improve if
necessary.

en.wikipedia.org/wiki/Program_o

Also, you missed the word



‘may’ when you mentioned
UNION. Your source states
“may run faster than”, not “will
be faster”. I’ve found that OR
is faster than UNION and a
quick google on the subject
confirms this:

mysqlperformanceblog.com/2007
vs-union-all-performance/

Your source,
bcarter.com/optimsql.htm was
apparently last updated in
1996 and I’d like to think
MySQL had changed quite a
bit since then.

If anyone’s looking into
speeding up their MySQL
stuff then
mysqlperformanceblog.com is
highly recommended, the
English isn’t always great
though and the navigation
sucks but give it a try.

To expand on what Dirk so
rightly said, Indexes are great
for tables where there will be
a lot of read (SELECT)
operations. But if you’re often
writing to a table then the
Indexes can slow it down
because of course the index
must be updated.

Could you please consider an
update Jean, which reflects
what Dirk and I have
mentioned?

Reply

Jean-
Baptiste
Jung said:
March 9,
2010 at
8:49 am
You’re right



about the
bcarter
source: I
didn’t
checked the
“last update”
date when
writing the
article, sorry
for this.

I rarely
update
posts, but I’ll
rewrite some
parts this
week,
according to
my busy
schedule.

Thanks a lot
for your
interest!

Reply

Timothy said: March 9,
2010 at 8:47 am
Also, here are a few more
details that could help:

1) Be wise with column types
(VarChar, Blob, Clob / Long
Text, etc). When using
something like int, varchar,
etc with a set length the SQL
server will know what to
expect when conducting
queries. If you use something
like Clob / Long Text, which
does not have a set limit,
then the server will not know
what to expect, so the queries
have to way of being
optimized. Basically, it means
that every query that involves
a column with such a type will
be slow. Only use these



variable types if you need to.

2) Using trims or other string
modifiers will greatly slow
down your queries. The
server will have to do this on
each row. Pretty logical when
you think about it. Any time
you are modifying a string or
other variable type within a
query you are adding a great
deal of overhead. If you can,
put these kind of things on
the server script side (PHP,
Ruby, etc).

3) If you have two tables, with
1 to 1 for every (key word
there) row, then why not use
just one table? Don’t make
more tables than you need.
Just because you’ll have
more columns doesn’t mean
you will have to SELECT
them all.

4) If you can, avoid putting
certain things in a table. Like
images. I often find out that
people store certain images in
a table as BLOBs and a
column for the image
mimetype. Then they query
the image and use something
like PHP to spit it out onto the
page. The only time I’ve really
seen this to be necessary is
with CAPTCHA images.
Where the image is stored as
a BLOB alongside a hash
representing the text in the
image. Though, you could
probably put the images in a
folder with random filenames
and have a table matching
filenames to hash values. But
that can open up some
security risks (like black-hats
creating their own look-up
table so that they can produce
scripts).



Reply

Jean-
Baptiste
Jung said:
March 9,
2010 at
5:29 pm
Thanks for
the
additional
tips!

Reply

Daniel said:
March 9, 2010
at 6:25 pm
in reply to your tip
3:

i disagree.
sometimes it can
make sense to split
up a table into two,
because searching
in very wide (lots of
columns) tables
also has a
performance
impact. splitting up
tables is pretty
useful if you only
search on a couple
of fields in this
table, and the
majority of the
other fields is just
“additional info”
such as
timestamps,
user_ip, file
locations etc. you
never consider
when looking up
records.
this also means
that it is easier to
keep your “index-



table” free from
variable length data
types as described
in tip 1

Reply

Tomasz Kowalczyk said:
March 9, 2010 at 1:53
pm
Very good list, I would also
add using ORMs such as
Doctrine / Propel [included in
frameworks such as symfony]
that are caching everything –
no need to remember that
things.

Reply

Sebastiaan
Stok said:
March 11,
2010 at
1:45 pm
NEVER
EVER USE
ORM!!!
That is
performance
killer number
one.

There are to
many bad
things about
Object
Relation
Mapping.
* You can’t,
you just
can’t
optimize the
query (no
realy)
* Having an
oject for
every row is
heavy of



memory
usage
* I even
heard about
an option to
buffer query
execution, to
do it in one
time. That is
not only
stupid. But it
is also very
dangerous! I
use
transactions
allot and
using an
ORM
system will
break this.

Some one I
know
decided on
using an
ORM, and is
not very
happy with
it.
But he can’t
switch since
that will
break the
coding.

And
something
else, ORM
will make
you brake
with almost
very design
principle and
pattern there
is.

Just use
plain old
SQL, it is
much better
and flexible.



Reply

mithu said: March 9, 2010
at 4:35 pm
Life saving tricks. Thankx.

Reply

CoryMathews said: March
9, 2010 at 5:07 pm
“Use join instead of sub
queries”

Depends on if the sub query
is in the select from or where
statement. So this advice
while normally true for selects
is not always true for the from
or where statement. Thus is
false.

“Use UNION instead of OR”

His benchmark says that but
every db I have worked with
says otherwise..

Reply

James Edinburgh said:
March 9, 2010 at 6:26
pm
Thanks for this information.

I’m just getting started in the
world of SQL and databases
and this is some solid advice.
I’ve been playing around with
WordPress and other PHP
based CMS systems and I
really really want to get
started and build my own
system, i’ll be sure to put
these tips to work when I do.

Reply



Mes favoris du 8-03-10 au
10-03-10 » Gilles Toubiana
9:03 am
your database [...]

Reply

» ce que j’ai vue depuis
mon retour ! oxynel, blog
communication - Agence de
communication Montpellier
11:03 am
[...] Du SQL, du SQL ou l’art
d’optimiser ses requêtes [...]

Reply

10 Astuces SQL pour
améliorer vos requêtes |
KubX said: March 11,
2010 at 7:51 am
your database. Tags:sql [...]

Reply

Harsh Athalye said: March
11, 2010 at 11:38 am
Good SQL tips. Optimizing
queries is such a huge topic
in itself, that a book can be
written around it. But basically
tips mentioned here are good
enough. I would add some
more:

1. Choose wise columns
when creating indexes.
Creating indexes on data
types of char, varchar or such
other sizable data types can
kill the performance
2. If you have indexes on



columns, try to avoid
wrapping column inside a
function
3. Convert IN clause to joins
4. Set based queries definitely
beat procedural approach like
cursors in terms of
performance

Reply

Brian said: March 12, 2010
at 2:03 am
Great tips there, I’m suprised
you’ve not mentioned the
mysql query cache, qcache.
This can dramatically speed
up mysql especially on high
traffic sites.

I must admit i’d not given
much thought to design, I
lumped all the fields in one
table which was fine when
the site had 100 entries but
now it has over 3000 things
are really starting to suffer
and I’m having to strip out the
database and organise it.

It goes to show that a little bit
of haste can really turn into a
lot of waste later on.

Reply

LISA TORRES said: March
13, 2010 at 10:18 am
The server will have to do
this on each row. Pretty
logical when you think about
it. Any time you are modifying
a string or other variable type
within a query you are adding
a great deal of overhead.

Reply



quicoto said: March 17,
2010 at 11:03 am
Nice I never though how bad
can be ask for “SELECT *”
without no LIMIT or without
asking for certain fields.

Regards

Reply

TDAH said: March 19,
2010 at 1:25 am
Man, I just tried these on my
db and they worked great,
thanks

Reply

Christian said: March 19,
2010 at 5:02 am
Wow, I did not know the
update query with the nice
“CASE” syntax until now.
Very helpful. Thanks.

Reply

Jonathan Good said: March
20, 2010 at 1:50 pm
Great article thanks for
sharing – we can all use
faster dbs!

Reply

Agnideb Mishra said:
March 20, 2010 at 10:32
pm
excellent article! The queries
are particularly very helpful for
a newbie like me. Thanks for
the awesome information.

Reply



Jack colt said: March 22,
2010 at 11:56 pm
Thanks for the tips. Most of
my websites are really slow in
loading. I tried using WP
super chache without much
success. It appears now that
the culprit lies in my design
and database.

Reply

Shukrit Verman said: March
27, 2010 at 11:15 pm
Thanks a bunch for this
article. I will try to fix my slow
blog using these tips

Reply

Chimpu Sharma said:
March 27, 2010 at 11:22
pm
I have always had to take my
web host’s help for running
sql queries. Thanks to this
article, I guess I would no
longer have to! Thanks again

Reply

Bob said: March 27, 2010
at 11:36 pm
“I tried using WP super cache
without much success.”

It is not working for me either.
Actually, while it is supposed
to speed up my blog, it is
actually slowing the blog
down I would try using the
database optimization tips laid
out in this article.

Reply



Vinith Shukla said: March
27, 2010 at 11:39 pm
Thank you very much for
these details; but for them, I
would not have known how to
optimize my SQL database!

Reply

Dan - LogoFoo.com said:
March 31, 2010 at 8:41
pm
Very helpful. By the way, I
think using SELECT * is not
really that harmful if you
combine it with the LIMIT
operator.

Reply

Blogger said: April 1, 2010
at 9:10 am
Hu, i had never thought that
those changes could speed
up my DB.
Thanks for collecting these
informations!

Reply

SQLを早くする10個の項目 |
アイビースター said: April 7,
2010 at 2:02 am
your database [...]

Reply

fireRoxy said: April 13,
2010 at 4:45 am
very useful tips. thank you
very much.

Reply



Savita Bisht said: April 22,
2010 at 11:20 pm
yeah, it is a nice article,
worked great for me.

Reply

Mundu said: April 29, 2010
at 11:06 am
Thanks so much for this
informative article. I now know
how to fix my extremely slow
blog

Reply

8 consigli e trucchi sql per
ottimizzare e rendere
performante un Database |
Pecciola said: April 30,
2010 at 12:33 am
[...] Fonte : Catswhocode [...]

Reply

Edward said: May 13, 2010
at 10:59 am
This post is very usefull,
thank you
I also heard about something
called stored queries so you
just call it by its name when
you do the query for example
“getnews()” but I’m a
complete newbie !

Reply

Michael said: May 13, 2010
at 11:37 am
Thanks for sharing this
information, it is very useful to
my visual basic programming.

Michael



Reply

Jamie said: May 25, 2010
at 10:51 am
This is indeed very helpful. I
appreciate the fact that you
are providing screenshots so
we would know we are on the
same track while following
your tutorial. Thanks so much
for sharing.

Reply

Johnson said: May 31,
2010 at 7:04 pm
Great tips, i’ve been
wondering if i could customise
my wordpress database, this
is too slow as posts
accurelates, anyone have
interests ?

Reply

Jon said: June 11, 2010
at 1:05 pm
I may have to come back to
this page very shortly…a lot
of good info here.

Reply

Jennifer R said: June 12,
2010 at 10:34 am
Could use DB cache reload
can increase the performance
of mySQL database?

Reply

Büyü said: June 18, 2010
at 10:12 am
Could use DB cache reload
can increase the performance



of mySQL database?

Reply

Alex Wolf said: June 20,
2010 at 11:16 am
Thanks for the limit tip, I
didn’t know about it.

Reply

Charlie said: August 3,
2010 at 1:52 pm
All good tips, particularly on
the use of UNION over OR.

As far as I know, in most
SQL databases, some uses of
OR prevent the use of an
index. So for large tables, it is
faster to scan the indices
multiple times rather than
searching the entire table
once.

Reply

Sumanta Sinha said:
August 20, 2010 at 5:09
am
Lately one of my PHP scripts
is making way too many sql
queries while it could easily
do the job by making fewer
queries. The reason: the
script developer did not
bother to optimize the scripts
so it could use the least
possible resource. He has
also stopped supporting the
project a year ago. Thanks to
my web host, I would have
never had known about this. I
would try your tips and see if
it helps at all. thanks

Reply



Felipe said: November 4,
2010 at 6:47 pm
Always refreshing to see
someone pop open the hood
and show how it is done in
the age of “just-use-my-
cuttie-pretty-web-2.0-
framework-and-it-will-take-
care-of-everything-for-you-in-
a-pinch”. Congrats.

Reply

Shawn said: June 21, 2012
at 11:49 am
I know it’s a bit of a late post
but…..”Avoid queries in
loops,” while i agree with you
that you shouldn’t keep
sending SQL to a database
while looping, i think your
example is *way* to simple to
be of use. You are essentially
hard coding the case values
which 1. Shouldn’t be hard
coded and 2. only
manageable for a very small
set. I believe a better
alternative is to go ahead and
use the looping statement and
GENERATE the SQL needed.
Ex. Update value 1; Update
value 2; update value 3,
update value N. That is, to
aggregate the SQL into a
string variable, AND THEN
send it to the database only
once and after it is generated.

Reply

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