Databases
StackOverflow2013
Postsdbo
POMySQL Innodb key length on secondary indexes
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POMySQL Innodb key length on secondary indexes
    primarykey
    data
    text
    <p>MySQL : Ver 14.12 Distrib 5.0.51b, for redhat-linux-gnu (x86_64) using EditLine wrapper</p> <p>sql_1:</p> <pre><code>SELECT SQL_NO_CACHE COUNT(*) FROM `ting_song_info`; </code></pre> <p>result :</p> <pre><code>+----------+ | COUNT(*) | +----------+ | 2637447 | +----------+ 1 row in set (0.42 sec) </code></pre> <p>explain :</p> <pre><code>+----+-------------+----------------+-------+---------------+-------------------+---------+------+---------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+-------+---------------+-------------------+---------+------+---------+-------------+ | 1 | SIMPLE | ting_song_info | index | NULL | total_listen_nums | 4 | NULL | 2769410 | Using index | +----+-------------+----------------+-------+---------------+-------------------+---------+------+---------+-------------+ </code></pre> <p>The sql_1 use the key <code>total_listen_nums</code>.</p> <p>Then appoint the key.</p> <p>sql_2 :</p> <pre><code>SELECT SQL_NO_CACHE COUNT(*) FROM `ting_song_info` USE KEY(`album_id`); </code></pre> <p>result :</p> <pre><code>+----------+ | COUNT(*) | +----------+ | 2637447 | +----------+ 1 row in set (5.21 sec) </code></pre> <p>explain:</p> <pre><code>+----+-------------+----------------+-------+---------------+----------+---------+------+---------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+----------------+-------+---------------+----------+---------+------+---------+-------------+ | 1 | SIMPLE | ting_song_info | index | NULL | album_id | 8 | NULL | 2769410 | Using index | +----+-------------+----------------+-------+---------------+----------+---------+------+---------+-------------+ </code></pre> <p>The key_len of total_listen_nums is shoter than album_id.</p> <p>Is this why sql_1 use total_listen_nums?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. UStadman
    1. USbloody numen
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POMySQL Innodb key length on secondary indexes
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POMySQL Innodb key length on secondary indexes
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POMySQL Innodb key length on secondary indexes
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhenever possible, please strip down the amount of information you're presenting to just the essentials. Code formatting, which makes it considerably easier to read, is done by indenting with four spaces.
      singulars
      1. POMySQL Innodb key length on secondary indexes
      1. UStadman
    2. COIt's clean now. ^_^
      singulars
      1. POMySQL Innodb key length on secondary indexes
      1. USbloody numen
    3. CODo try to post only what's necessary to communicate your point. Six lines of code to relay what's effectively a single number is not very effective.
      singulars
      1. POMySQL Innodb key length on secondary indexes
      1. UStadman
 

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