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Editorial Team
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Asked: 2026-05-27T23:14:04+00:00

I have a table that contain one primary key. When I run EXPLAIN SELECT

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I have a table that contain one primary key.
When I run

EXPLAIN SELECT * FROM news ORDER BY id ASC LIMIT 29

Mysql returns

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
1   SIMPLE           news    ALL      NULL           NULL    NULL      NULL     640     Using filesort

But by EXPLAIN SELECT *
FROM news
ORDER BY id ASC
LIMIT 28
it returns

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
1   SIMPLE          news    index   NULL           PRIMARY  4          NULL     28

SHOW INDEX FROM news ;

Table, Non_unique, Key_name, Seq_in_index, Column_name, Collation, Cardinality, Sub_part, Packed, Null, Index_type, Comment  
'news', 0, 'PRIMARY', 1, 'id', 'A', 640, , '', '', 'BTREE', ''
'news', 1, 'tarix', 1, 'tarix', 'A', 106, , '', '', 'BTREE', ''
'news', 1, 'yayindil', 1, 'yayin', 'A', 3, , '', '', 'BTREE', ''
'news', 1, 'yayindil', 2, 'dil', 'A', 7, , '', '', 'BTREE', ''

I checked it on other tables, they work fine also on limit 4000. What is going wrong? Why only under 29 limitations use indexes?

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1 Answer

  1. Editorial Team

    The optimiser is trying to select the cheapest execution path. With only 640 rows in the table it isn’t strange that the optimiser chooses a full scan. Load the table with 40000 rows and you will find that you have to increase the limit (probably to around 2000) before a full table scan is chosen.

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