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Preformace problem (maybe bug?) with multiple join on same table
Posted by: Joerg Plenert
Date: March 31, 2005 09:16AM

Hi !

select t0.a, t1.b, t2.b, t1.c, t3.b FROM `tab1` as t0 LEFT JOIN `tab2` as t1 ON t0.a = t1.a LEFT JOIN `tab3` as t2 ON t1.b = t2.a LEFT JOIN `tab4` as t3 ON t1.c = t2.a

is very slow.

Explain says

id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 index Lst 5 5650 Using index
1 SIMPLE t1 eq_ref PRIMARY,a PRIMARY 4 oc_dsu.t0.a 1 (null)
1 SIMPLE t2 eq_ref PRIMARY,a PRIMARY 4 oc_dsu.t1.b 1 (null)
1 SIMPLE t3 index bezeichnung 75 914 Using index

where the last looks scary !?

If I don't use t3 the speed is fine!

Using 4.1.10a

Is that a bug, a feature or just a poor select statement !?

Regards

Joerg Plenert

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