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Re: Performance bei SELECT
Posted by: Thomas Wiedmann
Date: January 20, 2012 12:11PM

Hallo Mark,
diese zwei Spalten sind meiner Meinung nach vollkommen überdimensioniert.

CREATE TABLE `items` (
[...]
`Brand` varchar(255) NOT NULL, 
[...]
`attr_gender` varchar(100) NOT NULL, 
[...]
KEY `Brand` (`Brand`), 
[...]

wirklich benötigt wird nur dieser Größe:

SELECT MAX(LENGTH(brand)), MAX(LENGTH(attr_gender)) FROM items;

+--------------------+--------------------------+
| MAX(LENGTH(brand)) | MAX(LENGTH(attr_gender)) |
+--------------------+--------------------------+
|                 57 |                        1 |
+--------------------+--------------------------+

deshalb würde ich diese zwei Spalten in etwa so kürzen und einen combined index darüber legen:

ALTER TABLE items
 MODIFY brand VARCHAR(80) NOT NULL,
 MODIFY attr_gender VARCHAR(10) NOT NULL;
 
ALTER TABLE items
 DROP KEY brand,
 ADD KEY idx_brand_gender (brand, attr_gender);

Jetzt bitte nochmal den Query mit EXPLAIN ausführen.
EXPLAIN SELECT items.Brand, 
       SUM(
            (SELECT SUM(its.PhysicalStock)
              FROM items_stock AS its
             WHERE its.ItemNrInt = items.ItemNrInt
           )
       ) AS stockValue
FROM items
LEFT JOIN ( SELECT ItemNrInt,MAX(OrderQty),MAX(FullPrice),MAX(OrderDate),MAX(ItemPriceNoVAT),MAX(Status)
              FROM invoicelines
             GROUP BY ItemNrInt
             ORDER BY NULL ) invoicelines
ON (invoicelines.ItemNrInt = items.ItemNrInt)
WHERE items.attr_gender = '8'
GROUP BY items.Brand;

Grüße
Thomas

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