How to select rows from partition in MySQL

Question

I made partition my 300MB table and trying to make select query from p0 partition with this command

SELECT * FROM employees PARTITION (p0);

But I am getting following error

ERROR 1064 (42000): You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version for the right syntax to use near '(p0)' at line 1

How to write select query to get data from specific partition?

Solution 1

Depending on you MySql version, PARTITION keyword does not exist until MySQL 5.6.2. You would be using MySQL 5.5 or even 5.1, but not 5.6. In case, you are using MySQL 5.1, then you can do some workaround like below

SELECT partition, count(ID)
FROM
(
    SELECT ID,
      case when condition then p1
           when condition then p2
      .....
      end as partition

    FROM
      table
) s1
GROUP BY partition

Note : The above solution is just workaround to get you desire output.

You may also try this query to count total number of rows for your partition.

SELECT table_rows as 'count(*)' FROM information_schema.partitions WHERE table_schema = schema() and table_name ='employees' and partition_name = 'p0';

Note : you may change table_schema = schema() to table_schema = 'yourschema'

Solution 2

Actually since MySQL 5.6 the supported syntax is:

SELECT * FROM table PARTITION (partitionName);

Solution 3

The correct form of the query is as below it works for me fine.

select * from employees partition (`p0`);

Solution 4

You are right, explicit selection of PARTITION is not supported in 5.1.54 Version. See this post

Solution 5

SELECT * FROM invoice_detail PARTITION (p1);

View more solutions

Comments

[Ravi]

ok no issue, just don't forget to accept, other will get the benefit

[Kad]

Sorry, i tested it and it seems this command selects all rows

[Ravi]

then, what was your problem?? you just said, you were unable to select rows. that is it.

[Kad]

I want to select rows from p0 partition of table. My table has 138167 row and result is : 138167 rows in set (17.42 sec)

[Hanky Panky]

As i mentioned above, check the quoted post. this SELECT is not supported in mysql 5.1

[Kad]

Yes i saw, if i cant select from partition why making partition allowed with this version?

[Ravi]

please check my updated post, that may help you to figure out, why it is there.

[Ravi]

find out the difference, when you executed the first query and when you executed the second one

[Ravi]

please check my Note, you need to change that with your schema name, whatever would be your schema name, just change it with that

[Kad]

I used second command that you wrote and returned this : +----------+ | count(*) | +----------+ | 16612 | +----------+ 1 row in set (0.00 sec)

[Ravi]

have you notice anything ?? now you got exact row count from your own partition (less number than previous one).

[Kad]

Yes i already know that partition done before. But my need is select rows from that partition. I think this row count comes from information_schema.partitions not actual partition.

[ducin]

Hey, select * from employees p0; - this is completely wrong! It returns all results, since p0 is treated as the table alias and not the partition name.

[Ravi]

@Kad any specific reason for removing from accepted answer after 4 Years ? :D

[Kad]

@ravi I was just checking my questions and account

[nagendra547]

Clear and precise! :)

[Nico Haase]

Please do not provide querys that are widely open for SQL injection

[Nico Haase]

Please add all relevant information to the question instead of linking to external pages

[clearlight]

@NicoHaase You should explain what you mean a little more. How is that susceptible to injection?

[Nico Haase]

@clearlight just have a look at the previous version of that answer

[JMoura]

It doesn't answer the OP question plus its not specified the potential growth of this table during time to recommend not partitioning or whatsoever. You might share your opinions as a comments not answers to questions.