Databases
StackOverflow2013
Postsdbo
POImprove MySQL Query with IN Subquery
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POImprove MySQL Query with IN Subquery
    primarykey
    data
    text
    <p>I hava a table <code>items</code> and a table <code>item_attributes</code>.</p> <p>For simplicity let's say my table item has a column <code>id</code> and a column <code>name</code>. Of cource there is a index on the <code>id</code> column.</p> <p>the <code>item_attributes</code> table has the columns <code>id</code>, <code>item_id</code>, <code>attribute_name</code> and <code>attribute_value</code> and an index ON <code>attrubute_name</code></p> <p>Now I want to query all items with a specific attribut without using a join.</p> <p>I do this with the following query:</p> <pre><code>SELECT * FROM items i WHERE i.id IN ( SELECT item_id FROM item_attributes a WHERE a.attribute_name = 'SomeAttribute' AND a.attribute_value = 'SomeValue' ) </code></pre> <p>the SubQuery itself runs fast.</p> <p>If I execute the query itself first and use the result for an IN query</p> <pre><code>SELECT * FROM items i WHERE i.id IN (1,3,5,7,10,...) </code></pre> <p>it is fast, too.</p> <p>However, combined the query is very, very slow (>2 secs.) If I investigate the query plan I see why: MySQL does a full table scan on the items table instead of executing the subquery first and using the result for an index query.</p> <pre><code>1, 'PRIMARY', 'items', 'ALL', '', '', '', '', 149726, 'Using where' 2, 'DEPENDENT SUBQUERY', 'item_attributes', 'index_subquery', 'IDX_ATTRIBUTE_NAME', 'IDX_ATTRIBUTE_NAME', '4', 'func', 1, 'Using where' </code></pre> <p>Is there a way to optimize this query? I know that the subquery will always return only a small resultset (&lt;100 rows).</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USJürgen Steinblock
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POImprove MySQL Query with IN Subquery
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POImprove MySQL Query with IN Subquery
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POImprove MySQL Query with IN Subquery
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhy you can not use JOIN?
      singulars
      1. POImprove MySQL Query with IN Subquery
      1. USsll
    2. COWhat prompts you to want to do this without the use of a `JOIN`?
      singulars
      1. POImprove MySQL Query with IN Subquery
      1. USRaj More
    3. COI can't use join because this is only a small piece of the full picture. I use C# with an ORM and I just add the `WHERE master.primarykey IN (dynamic subquery)` piece to an existing in memory query object that is later converted to plain SQL. I can't use a JOIN because I would need to add a group by clause but that would restrict the calling function.
      singulars
      1. POImprove MySQL Query with IN Subquery
      1. USJürgen Steinblock
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload