Hello,

I have two tables:

CREATE TABLE categories (
   CategoryNumber int(11) NOT NULL,
   ItemNumber int(11) NOT NULL,
   KEY CategoryNumber (CategoryNumber),
   KEY ItemNumber (ItemNumber)
);

CREATE TABLE items (
   ItemNumber int(11) NOT NULL auto_increment,
   Description varchar(100) NOT NULL,
   Price bigint(20) unsigned NOT NULL,
   KEY Price (Price)
);

Each item can have multiple categories.
Each table contains more than 1 million records.

This kind of query gets executed a lot:

  SELECT I.* FROM 
    items AS I, 
    categories AS C
  WHERE 
     C.CategoryNumber = 123 AND 
     C.ItemNumber = I.ItemNumber AND 
     I.Price >= 1000
  LIMIT 0,51;

I would like to improve the performance of this query.

My question is: 
  Would a double index on both fields in the categories table
  increase performance?
  In other words, would this structure be better:

CREATE TABLE categories (
   CategoryNumber int(11) NOT NULL,
   ItemNumber int(11) NOT NULL,
   KEY CategoryItem (CategoryNumber,ItemNumber)
);


Thanks!

Tim






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