Simple SELECT/WHERE query slow. Should I index a BIT field? [duplicate] - sql

Question

This question already has answers here:
Should I index a bit field in SQL Server?
(18 answers)
Closed 8 years ago.
The following query takes 20-25 seconds to run
SELECT * from Books WHERE IsPaperback = 1
Where IsBundle is a BIT field. There's about 500k rows, and about 400k currently have this field set.
I also have a BIT field called IsBundle and only 900 records have this set. Again, execution time is about 20-25 seconds.
How can I speed up such a simple query?

Answer 1

Indexing a bit column will result in two parts, true and false. If the data is split 50/50 the gain will be 'some'. When it is 90/10 and you query the 10 part, yes it will make a difference.
You should first narrow down your result set column wise. Then, if you see you just need a few columns, and you execute this query a lot, you could even include those few fields in the index. Then there is no need for a lookup in the table itself.

Answer 2

First of all i would implicitly call out the columns,
select
field1
, field2
, field3
from books
where IsPaperback = 1;
this seems to be a small thing, but when you use star (*) for column selection, the DB has to look up the column names prior to actually performing the call.
do you have a index on IsPaperback ? that would impact the above query more than having an index on the IsBundle
if you had a condition of IsBundle = 1 then i would think that would be need for an index on that field.

Answer 3

Add an Index for IsPaperback
Try making it an int, or tinyint. The latest processors actually process 32 bit words faster than bytes.
This query should take no more than a couple of milliseconds.
You should not have a separate column for IsPaperback and IsBundle. It should be a Type column where Paperback and Bundle are the vaules.
Before the query set profiling on
SET profiling = 1
After the query show profiles:
SHOW PROFILES
It seems there are some out there that do not believe this query should take only a few milliseconds.
For those that down voted this answer without understanding what I said was true.
I found a table "cities" with 332,127 Records
In this table Russia has 929 cities
These benchmarks were preformed on a GoDaddy Server IP 50.63.0.80
This is a GoDaddy Virtual Dedicated Server
On average I find sites hosted on GoDaddy to have the worst performance.
$time = microtime(true);
$results = mysql_query("SELECT * FROM `cities` WHERE `country` LIKE 'RS'");
echo "\n" . number_format(microtime(true)-$time,6)."\n";
$time = microtime(true);
while ($row = mysql_fetch_array($results, MYSQL_NUM)){$r[]=$row;}
echo "\n" . number_format(microtime(true)-$time,6);
Results:
With Index: 2.9mS
0.002947 Seconds : $results = mysql_query("SELECT * FROM `cities` WHERE `country` LIKE 'RS'");
0.000081 Seconds : while ($row = mysql_fetch_array($results, MYSQL_NUM)){$r[]=$row;}
Without Index 93mS
0.093939 Seconds : $results = mysql_query("SELECT * FROM `cities` WHERE `country` LIKE 'RS'");
0.000073 Seconds : while ($row = mysql_fetch_array($results, MYSQL_NUM)){$r[]=$row;}
Then in phpMyAdmin Profiling:
SET PROFILING = ON;
SELECT * FROM `cities` WHERE `country` LIKE 'RS';
SHOW PROFILE;
Result:
Execution of the Query took 0.0000003 seconds
starting 0.000020
checking permissions 0.000004
Opening tables 0.000006
init 0.000007
optimizing 0.000003
executing 0.000003 ******
end 0.000004
query end 0.000003
closing tables 0.000003
freeing items 0.000010
logging slow query 0.000003
cleaning up 0.000003
Without Index
Execution of the Query took 0.0000012 seconds
starting 0.000046
checking permissions 0.000006
Opening tables 0.000010
init 0.000021
optimizing 0.000006
executing 0.000012 ******
end 0.000003
query end 0.000004
closing tables 0.000003
freeing items 0.000017
logging slow query 0.000004
cleaning up 0.000003
In phpMyAdmin doing a Search with Profiling turn on
GoDaddy Server Sending Data 92.6 ms
SELECT * FROM `cities` WHERE `country` LIKE 'RS' LIMIT 1000
Showing rows 0 - 928 (929 total, Query took 0.0907 sec)
Profiling Results:
Starting 52 µs
Checking Permissions 7 µs
Opening Tables 23 µs
System Lock 12 µs
Init 34 µs
optimizing 10 µs
Statistics 23 µs
Preparing 17 µs
Executing 4 µs
Sending Data 92.6 ms
End 18 µs
Query End 4 µs
Closing Tables 15 µs
Freeing Items 27 µs
Logging Slow Query 4 µs
Cleaning Up 5 µs
In phpMyAdmin doing a Search with Profiling turn on
On my Server, Sending Data 1.8mS
SELECT * FROM `cities` WHERE `country` LIKE 'RS' LIMIT 1000
Showing rows 0 - 928 (929 total, Query took 0.0022 sec)
Starting 27 µs
Checking Permissions 5 µs
Opening Tables 11 µs
System Lock 7 µs
Init 14 µs
Optimizing 5 µs
Statistics 43 µs
Preparing 6 µs
Executing 2 µs
Sending Data 1.8 ms
End 5 µs
Query End 3 µs
Closing Tables 5 µs
Freeing Items 13 µs
Logging Slow Query 2 µs
Cleaning Up 2 µs
Just to show the importance of an index.Over 400x Improvement.
A table with 5,480,942 Records and a Query that Returns 899 Rows
$time = microtime(true);
$results = mysql_query("SELECT * FROM `ipLocations` WHERE `id` = 33644");
echo "\n" . number_format(microtime(true)-$time,6);
$time = microtime(true);
while ($row = mysql_fetch_array($results, MYSQL_NUM)){$r[]=$row;}
echo "\n" . number_format(microtime(true)-$time,6);
No index
0.402005
0.001264
With Index (426x Faster)
0.001716
0.001962