MySQL的計數，並選擇從一個分區

Original post: http://anothermysqldba.blogspot.com/2013/05/mysql-count-and-select-from-partition.html

MySQL論壇上有一個問題，對如何計算每個分區的行。 
我想通它將使一個良好的博客文章。 

首先，這些分區審查和至少讓你開始有一些很好的鏈接。 這些網頁使用的例子在這裡參考的例子開始。 

• http://dev.mysql.com/doc/refman/5.6/en/partitioning.html
• http://dev.mysql.com/tech-resources/articles/mysql_55_partitioning.html


> CREATE TABLE t2
-> (
-> dt DATE
-> )
-> PARTITION BY RANGE (TO_DAYS(dt))
-> (
-> PARTITION p01 VALUES LESS THAN (TO_DAYS('2007-01-01')),
-> PARTITION p02 VALUES LESS THAN (TO_DAYS('2008-01-01')),
-> PARTITION p03 VALUES LESS THAN (TO_DAYS('2009-01-01')),
-> PARTITION p04 VALUES LESS THAN (MAXVALUE));

> desc t2;
+-------+------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------+------+-----+---------+-------+
| dt | date | YES | | NULL | |
+-------+------+------+-----+---------+-------+ 

INSERT INTO t2 VALUES ('2007-02-02'),('2008-02-02'),('2009-02-02'),(CURDATE());

Query OK, 4 rows affected (0.04 sec)




OK所以現在我們可以選擇從分區以及指望從他們.. 


> select count(*) from t2;
+----------+
| count(*) |
+----------+
| 4 |
+----------+ 

> explain partitions select count(*) from t2 \G

*************************** 1. row ***************************

id: 1

select_type: SIMPLE

table: t2

partitions: p01,p02,p03,p04

type: ALL

possible_keys: NULL

key: NULL

key_len: NULL

ref: NULL

rows: 5

Extra: NULL

>選擇* T2分區（P02）;

+ ------------ +

DT |

+ ------------ +

| 2007-02-02 |

+ ------------ +

>選擇* T2分區（P04）;

+ ------------ +

DT |

+ ------------ +

| 2009-02-02 |

2013年5月15日| |

+ ------------ +

> SELECT * FROM T2分區（P02，P04）;

+ ------------ +

DT |

+ ------------ +

| 2007-02-02 |

| 2009-02-02 |

2013年5月15日| |

+ ------------ +

> SELECT COUNT（*）從t2的分區（P04）;

+ ---------- +

| COUNT（*）|

+ ---------- +

| 2 |

+ ---------- +

希望這會有所幫助。