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Archive for May, 2011

MySQL’s List Partition Key

with 6 comments

While reviewing some material and explaining list partitioning in MySQL, I heard a rumor that sounded false. The rumor was that you can’t partition on anything other than the primary key column. That’s untrue, you can partition on another column provided it’s an integer column.

It appears the culprit that led to the rumor is a misunderstanding around ERROR 1503, which returns the following:

ERROR 1503 (HY000): A PRIMARY KEY must include ALL COLUMNS IN the TABLE's partitioning function

The problem can be recreated by defining a table with an inline primary key constraint instead of an INDEX on the auto incrementing column. Here’s an example of how to create the error message:

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CREATE TABLE franchise
( franchise_id     INT UNSIGNED PRIMARY KEY AUTO_INCREMENT
, franchise_number INT UNSIGNED
, franchise_name   VARCHAR(20)
, city             VARCHAR(20)
, state            VARCHAR(20))
PARTITION BY LIST(franchise_number)
( PARTITION offshore VALUES IN (49,50)
, PARTITION west VALUES IN (34,45,48)
, PARTITION desert VALUES IN (46,47)
, PARTITION rockies VALUES IN (38,41,42,44));

The table should be defined without the inline PRIMARY KEY constraint on the auto incrementing column when you want to partition on another column. An index on the auto incrementing column doesn’t conflict with primary key rules. The correct syntax for a list partition would be:

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CREATE TABLE franchise
( franchise_id     INT UNSIGNED AUTO_INCREMENT
, franchise_number INT UNSIGNED
, franchise_name   VARCHAR(20)
, city             VARCHAR(20)
, state            VARCHAR(20)
, INDEX idx (franchise_id)) engine=innodb
PARTITION BY LIST(franchise_number)
( PARTITION offshore VALUES IN (49,50)
, PARTITION west VALUES IN (34,45,48)
, PARTITION desert VALUES IN (46,47)
, PARTITION rockies VALUES IN (38,41,42,44));

The same problem can manifest itself on range partitioning. The fix is the same and here’s a code example:

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CREATE TABLE ordering
( ordering_id      INT UNSIGNED AUTO_INCREMENT
, item_id          INT UNSIGNED
, rental_amount    DECIMAL(15,2)
, rental_date      DATE
, INDEX idx (ordering_id))
PARTITION BY RANGE(item_id)
( PARTITION jan2011 VALUES LESS THAN (10000)
, PARTITION feb2011 VALUES LESS THAN (20000)
, PARTITION mar2011 VALUES LESS THAN (30000));

The MySQL 5.6 Partitioning Keys, Primary Keys, and Unique Keys article is the key reference. It’s unfortunate that MySQL can’t partition on something other than an integer with PARTITION BY LIST syntax (check the changes in MySQL 5.6 online documentation). As you’ll notice in my more recent comment back to Tim, you can when you change the SQL phrase to PARTITION BY LIST COLUMNS. MySQL now has another feature that the Oracle Database 11g supports, that is list partitioning on variable-length string columns.

There are a few required changes but here’s a working example. The index must work against the auto incrementing column. The example comes my reply to Tim, who raised a great question.

CREATE TABLE franchise
( franchise_id     INT UNSIGNED AUTO_INCREMENT
, franchise_number INT UNSIGNED
, franchise_name   VARCHAR(20)
, city             VARCHAR(20)
, state            VARCHAR(20)
, KEY idx (franchise_id)) engine=innodb
PARTITION BY LIST COLUMNS (franchise_name)
( PARTITION m VALUES IN ('McDonald','Maggiano')
, PARTITION p VALUES IN ('Pappa John','Pizza Hut')
, PARTITION t VALUES IN ('Taco Bell','Taco Time'));

While that works, the better approach creates two unique constraints. One unique constraint on the natural key of the franchise_number and franchise_name, which serves to optimize access to data sets looking data up in the table based on a natural key search. Another unique constraint on the surrogate (auto incrementing column) and the two natural key columns, which optimizes joins from foreign keys to the partitioned table’s primary key.

CREATE TABLE franchise
( franchise_id     INT UNSIGNED AUTO_INCREMENT
, franchise_number INT UNSIGNED
, franchise_name   VARCHAR(20)
, city             VARCHAR(20)
, state            VARCHAR(20)
, UNIQUE ink (franchise_number, franchise_name)
, UNIQUE enk (franchise_id, franchise_number, franchise_name)) engine=innodb
PARTITION BY LIST COLUMNS (franchise_name)
( PARTITION m VALUES IN ('McDonald','Maggiano')
, PARTITION p VALUES IN ('Pappa John','Pizza Hut')
, PARTITION t VALUES IN ('Taco Bell','Taco Time'));

Somebody asked for a composite partitioning (MySQL terminology is subpartitioning) example, so here it is:

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CREATE TABLE ordering
( ordering_id      INT UNSIGNED AUTO_INCREMENT
, item_id          INT UNSIGNED
, store_id         INT UNSIGNED
, rental_amount    DECIMAL(15,2)
, rental_date      DATE
, INDEX idx (ordering_id))
PARTITION BY RANGE(item_id)
  SUBPARTITION BY HASH(store_id) SUBPARTITIONS 4
( PARTITION jan2011 VALUES LESS THAN (10000)
, PARTITION feb2011 VALUES LESS THAN (20000)
, PARTITION mar2011 VALUES LESS THAN (30000));

Hope this helps those researching ERROR 1503 on list or range partitioning.

Written by maclochlainn

May 9th, 2011 at 8:27 pm

MySQL Virtual Columns?

with one comment

While preparing for next week’s classes, I ran across a new future feature of MySQL – the virtual column. It appears, according to the article, that MySQL will have virtual columns in MySQL 6.

The syntax is virtually identical to that found in Oracle databases. For example, here’s what suppose to work in the future:

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CREATE TABLE salary
( salary_id    INT UNSIGNED PRIMARY KEY AUTO_INCREMENT
, salary       DOUBLE NOT NULL
, bonus        DOUBLE
, compensation DOUBLE AS (salary + bonus));

It’s virtually (excuse the pun) how it would work in Oracle Database 11g. I wonder what else we see move over into MySQL. Just a note, virtual columns moved from Oracle RDB (a prior acquisition from Digital Equipment Corporation in 1996) to the Oracle Database 11g.

Equivalent syntax in Oracle Database 11g would be like this for concatenation:

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CREATE TABLE employee
( employee_id NUMBER
, first_name  VARCHAR2(20)
, last_name   VARCHAR2(20)
, full_name   VARCHAR2(41) AS (first_name || ' ' || last_name));

And like this for a math operation (like the one noted above for a future release of MySQL):

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CREATE TABLE salary
( salary_id    NUMBER       CONSTRAINT pk_salary PRIMARY KEY
, salary       NUMBER(15,2) CONSTRAINT nn_salary_01 NOT NULL
, bonus        NUMBER(15,2)
, compensation NUMBER(15,2) AS (salary + bonus));

Written by maclochlainn

May 5th, 2011 at 7:18 pm

Posted in MySQL,Oracle,sql