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Asked: 2026-06-15T21:27:42+00:00

I’m running queries on an old mysql database and many queries are taking far

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I’m running queries on an old mysql database and many queries are taking far longer than they should. for example this one, ad_vehicle has 60000 rows, id_ad_link has 25000

SELECT * FROM autotalk_identicar_old.ad_vehicle 
left join autotalk_identicar_old.id_ad_link on autotalk_identicar_old.ad_vehicle.vehiclekey=autotalk_identicar_old.id_ad_link.rbvehiclekey;

duration is 2.323 seconds, fetch is still going 12 minutes after hitting execute (using mysql workbench, not sure if that makes any difference though). running in a vm with 3 cores of my amd quad core @ 3.4ghz with 1gb memory

I don’t think there are any indexes/primary keys however would that make such a big difference?

first few rows of ad_vehicle

A145 00AA, PV, ALFA, 145, 2000, 3HBm, 1.6, , , , , P, , 5, 1596, , , 32995,  , , 3HBm 1.6p
A145 00AB, PV, ALFA, 145, 2000, 3HBm, 1.7, , , , , P, , 5, 1712, , , 41995,  , , 3HBm 1.7p
A145 01AA, PV, ALFA, 145, 2001, 3HBm, 1.6, , , , , P, , 5, 1596, , , 32995,  , , 3HBm 1.6p
A145 01AB, PV, ALFA, 145, 2001, 3HBm, 1.7, , , , , P, , 5, 1712, , , 41995,  , , 3HBm 1.7p
A145 02AA, PV, ALFA, 145, 2002, 3HBm, 1.6, , , , , P, , 5, 1596, , , 32995,  , , 3HBm 1.6p
A145 02AB, PV, ALFA, 145, 2002, 3HBm, 1.7, , , , , P, , 5, 1712, , , 41995,  , , 3HBm 1.7p
A145 95AA, PV, ALFA, 145, 1995, 3HBm, 1.6, , L, , , P, , 4, 1596, , , 32995,  , , 3HBm 1.6p L
A145 95AB, PV, ALFA, 145, 1995, 3HBm, 1.7, ELEGANTE, L, , , P, , 4, 1712, , , 41995,  , , 3HBm 1.7p ELEGANTE L
A145 96AA, PV, ALFA, 145, 1996, 3HBm, 1.6, , L, , , P, , 4, 1596, , , 32995,  , , 3HBm 1.6p L
A145 96AB, PV, ALFA, 145, 1996, 3HBm, 1.7, ELEGANTE, L, , , P, , 4, 1712, , , 41995,  , , 3HBm 1.7p ELEGANTE L
A145 97AA, PV, ALFA, 145, 1997, 3HBm, 1.6, , L, , , P, , 4, 1596, , , 32995,  , , 3HBm 1.6p L
A145 97AB, PV, ALFA, 145, 1997, 3HBm, 1.7, ELEGANTE, L, , , P, , 4, 1712, , , 41995,  , , 3HBm 1.7p ELEGANTE L
A145 98AA, PV, ALFA, 145, 1998, 3HBm, 1.6, , L, , , P, , 4, 1596, , , 32995,  , , 3HBm 1.6p L
A145 98AB, PV, ALFA, 145, 1998, 3HBm, 1.7, ELEGANTE, L, , , P, , 4, 1712, , , 41995,  , , 3HBm 1.7p ELEGANTE L
A145 98AC, PV, ALFA, 145, 1998, 4SDm, 2.5, , , , , P, , 5, 2492, , , 65998,  , , 4SDm 2.5p
A145 99AA, PV, ALFA, 145, 1999, 3HBm, 1.7, ELEGANTE, L, , , P, , 4, 1712, , , 41995,  , , 3HBm 1.7p ELEGANTE L
A145 99AB, PV, ALFA, 145, 1999, 3HBm, 1.6, , L, , , P, , 4, 1596, , , 32995,  , , 3HBm 1.6p L
A146 00AA, PV, ALFA, 146, 2000, 5HBm, 1.6, , TS, , , P, , 5, 1596, , , 37995,  , , 5HBm 1.6p TS
A146 01AA, PV, ALFA, 146, 2001, 5HBm, 1.6, , TS, , , P, , 5, 1596, , , 38995,  , , 5HBm 1.6p TS

first few rows of id_ad_link

4   10  DHJT 94AA   1994    REDUNDANT   HIJET
12  971 A33  95AA   1995    REDUNDANT   ALFA33
13  971 A33  95AB   1995    REDUNDANT   ALFA33
14  971 A33  95AC   1995    REDUNDANT   ALFA33
61  973 A146 95AB   1995    REDUNDANT   146
60  973 A146 95AA   1995    REDUNDANT   146
59  973 A145 02AB   2002    REDUNDANT   145
58  973 A145 02AA   2002    REDUNDANT   145
57  973 A145 01AB   2001    REDUNDANT   145
56  973 A145 01AA   2001    REDUNDANT   145
55  973 A145 00AB   2000    REDUNDANT   145
54  973 A145 99AB   1999    REDUNDANT   145
53  973 A145 99AA   1999    REDUNDANT   145
52  973 A145 98AC   1998    REDUNDANT   145
45  973 A145 95AB   1995    REDUNDANT   145
44  973 A145 95AA   1995    REDUNDANT   145
70  973 A146 98AB   1998    REDUNDANT   146
71  973 A146 98AC   1998    REDUNDANT   146
72  973 A146 99AA   1999    REDUNDANT   146
73  973 A146 00AA   2000    REDUNDANT   146

UPDATE:

here’s the result of 

explain SELECT * FROM autotalk_identicar_old.ad_vehicle 
left join autotalk_identicar_old.id_ad_link on autotalk_identicar_old.ad_vehicle.vehiclekey=autotalk_identicar_old.id_ad_link.rbvehiclekey;

id, select_type, table,       type,    possible_keys, key,  key_len, ref, rows,   Extra
'1', 'SIMPLE', 'ad_vehicle', 'ALL',        NULL,     NULL,   NULL,  NULL, '60433', ''
'1', 'SIMPLE', 'id_ad_link', 'ALL',        NULL,     NULL,   NULL,  NULL, '25571', ''
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1 Answer

  1. Editorial Team

    Try creating an index on the foreign key:

    create index id_ad_link_rbvehiclekey_index on id_ad_link(rbvehiclekey);

    Without this index, each row of ad_vehicle will cause a full tablescan on id_ad_link.
    With the index, each row of ad_vehicle will result in a few index pages being accessed (probably in-memory) and as few pages read to fetch the joined rows, because the index stores the page(s) to find the rows.

    Minimizing disk I/O is critical to performance, because it’s at least 1000 times slower than memory operations.

    Indexes make a huge difference, especially on columns used for joins (like foreign keys)

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