Re: combined or single indexes?

[Shawn Green (MySQL)]

On 7/21/2010 1:02 PM, Tompkins Neil wrote:
> Hi
> 
> So Just running a basic query I get returned the following :
> 
> table,type,possible_keys,key,key_len,ref,rows,Extra,
> Products,ALL,,,,,9884,where used,
> 
> Therefore, I assume "*ALL*" is the worst possible type and should look at
> adding a an index to this particular field ?
> 

Why assume when the manual is right there to remove all doubt?

http://dev.mysql.com/doc/refman/5.1/en/explain-output.html
####
ALL

A full table scan is done for each combination of rows from the previous 
tables. This is normally not good if the table is the first table not 
marked const, and usually very bad in all other cases. Normally, you can 
avoid ALL by adding indexes that enable row retrieval from the table 
based on constant values or column values from earlier tables.
####




-- 
Shawn Green
MySQL Principle Technical Support Engineer
Oracle USA, Inc.
Office: Blountville, TN