MySQL キーパティショニング

CREATE TABLE table_name (...
		)
PARTITION BY KEY()
PARTITIONS n;

CREATE TABLE k1 (
		id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
		name VARCHAR(20)
		)
PARTITION BY KEY()
PARTITIONS 2;

INSERT INTO k1(name) VALUES("a"),("b"),("c");

EXPLAIN PARTITIONS SELECT * FROM k1 WHERE id=1;
EXPLAIN PARTITIONS SELECT * FROM k1 WHERE id=2;

mysql> EXPLAIN PARTITIONS SELECT * FROM k1 WHERE id=1\G
*************************** 1. row ***************************
	   id: 1
  select_type: SIMPLE
	table: k1
   partitions: p0
	 type: const
possible_keys: PRIMARY
	  key: PRIMARY
      key_len: 4
	  ref: const
	 rows: 1
	Extra:
1 row in set (0.00 sec)
mysql>  EXPLAIN PARTITIONS SELECT * FROM k1 WHERE id=2\G
*************************** 1. row ***************************
	   id: 1
  select_type: SIMPLE
	table: k1
   partitions: p1
	 type: const
possible_keys: PRIMARY
	  key: PRIMARY
      key_len: 4
	  ref: const
	 rows: 1
	Extra:
1 row in set (0.00 sec)

CREATE TABLE k2 (
		name VARCHAR(20) PRIMARY KEY
		)
PARTITION BY KEY(name)
PARTITIONS 3;
INSERT INTO k2(name) VALUES("a"),("b"),("c");
EXPLAIN PARTITIONS SELECT * FROM k2 WHERE name="a";