I have a MyISAM table holding images with field types bigint(20), mediumblob, 
varchar(255), blob and tinyint(3).  The table has grown to over 800 MB and over 
6,000 rows.  In the past week, performance has been about 15-20 seconds to run 
the following select statement which pulls only 16 maximum rows:

SQL1) SELECT field1, field2, andUpToField10 FROM theTable WHERE field2 = 
$aField2Value OR field1 = 1 OR field1 = 2 ORDER BY field1 ASC

Basically I always pull the first 2 images in the table via the primary key 
field1 and upto 14 additional images depending on a foreign key field2.  field2 
can have up to 14 repeated/duplicate entries.

My working solution is that I have since split this into 2 select statements:
SQL2) SELECT field1, field2, andUptoField10 FROM theTable WHERE field1 = 1 OR 
field1 = 2 ORDER BY field1 ASC
SQL3) SELECT field1, field2, andUptoField10 FROM theTable WHERE field2 = 
$aField2Value ORDER BY field1 ASC
and performance is back to "instantaneous" (as far as web responsiveness is 

Can someone explain why SQL1 took so long to run as compared with running SQL2 
and SQL3 ?

Before splitting the statements, I also tried from phpmyadmin (Check table, 
Aalyze table, Optimize table) and creating an INDEX on field2, but I noticed no 
performance increase.  Before explicitly adding an INDEX, the space usage in 
phpmyadmin already showed Type:Index using several bytes.  The table still has 
the INDEX I explicitly created.

Can someone explain to me INDEXing ?  I was thinking of field2 and field3 for 
an INDEX (since field3 holds a number from 1 - 14 and the composite key "field1 
field2" would be unique), but I seem to be home free already.  I would just 
like to know "why" performance slowed and then "why" it improved with my 


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