MySQL Cookbook 学习笔记-02

1、分组后查找最大或最小值
2、根据“日期-时间”分组
3、“分组计算” 和 “全局计算” 同时存在查询中
4、删除一行数据，sequence 列会重新生成吗？
5、sequence 列指定值插入，不是我认为的不能指定值哦！
6、删除最大 sequence 行，对以后插入新行 sequence 值的影响
7、获取序列的值
8、设定序列的初始值
9、创建多重序列
10、使用序列产生计数器

______________________________________________________________

1、分组后查找最大或最小值

（Recipe 8.14. Finding Smallest or Largest Summary Values）

表和数据：

mysql> select * from driver_log;
+--------+-------+------------+-------+
| rec_id | name  | trav_date  | miles |
+--------+-------+------------+-------+
|      1 | Ben   | 2006-08-30 |   152 |
|      2 | Suzi  | 2006-08-29 |   391 |
|      3 | Henry | 2006-08-29 |   300 |
|      4 | Henry | 2006-08-27 |    96 |
|      5 | Ben   | 2006-08-29 |   131 |
|      6 | Henry | 2006-08-26 |   115 |
|      7 | Suzi  | 2006-09-02 |   502 |
|      8 | Henry | 2006-09-01 |   197 |
|      9 | Ben   | 2006-09-02 |    79 |
|     10 | Henry | 2006-08-30 |   203 |
+--------+-------+------------+-------+

MIN()，MAX() 的比较范围是指定的范围（如：全表，各组内，where指定范围），但却不能比较各组值的大小！

全表：

mysql> select min(miles), max(miles) from driver_log;
+------------+------------+
| min(miles) | max(miles) |
+------------+------------+
|         79 |        502 |
+------------+------------+

各组内：

mysql> select name, min(miles) ,max(miles) from driver_log-> group by name;
+-------+------------+------------+
| name  | min(miles) | max(miles) |
+-------+------------+------------+
| Ben   |         79 |        152 |
| Henry |         96 |        300 |
| Suzi  |        391 |        502 |
+-------+------------+------------+

where指定范围：

mysql> select min(miles), max(miles) from driver_log-> where trav_date < '2006-09-01';
+------------+------------+
| min(miles) | max(miles) |
+------------+------------+
|         96 |        391 |
+------------+------------+

替代办法：对分组后的值排序，取出第一个，即为最大或最小（有缺陷哦~~~如果最大或最小存在多个就不对了）

mysql> select name , sum(miles) as  total_miles-> from driver_log-> group by name-> order by total_miles desc;
+-------+-------------+
| name  | total_miles |
+-------+-------------+
| Henry |         911 |
| Suzi  |         893 |
| Ben   |         362 |
+-------+-------------+
取各组最大值： 
mysql> select name , sum(miles) as  total_miles-> from driver_log-> group by name-> order by total_miles desc limit 1;
+-------+-------------+
| name  | total_miles |
+-------+-------------+
| Henry |         911 |
+-------+-------------+
当最大、最小值存在重复时的处理办法：

查询数据如下

mysql> select left(name,1) as letter, count(*) as count-> from states-> group by letter-> order by count desc;
+--------+-------+
| letter | count |
+--------+-------+
| M      |     8 |
| N      |     8 |
| I      |     4 |
| A      |     4 |
| W      |     4 |
| O      |     3 |
| C      |     3 |
| K      |     2 |
| S      |     2 |
| T      |     2 |
| V      |     2 |
| L      |     1 |
| P      |     1 |
| R      |     1 |
| U      |     1 |
| D      |     1 |
| F      |     1 |
| G      |     1 |
| H      |     1 |
+--------+-------+
取出各组最大的记录

方式1：

mysql> set @max = (select count(*) from states-> group by left(name,1) order by count(*) desc limit 1);mysql> select left(name,1) as letter, count(*) as count from states-> group by letter having count = @max;
+--------+-------+
| letter | count |
+--------+-------+
| M      |     8 |
| N      |     8 |
+--------+-------+
方式2： 

mysql> select left(name,1) as letter ,count(*) as count from states-> group by letter having count =-> ( select count(*) from states-> group by left(name,1) order by count(*) desc limit 1);
+--------+-------+
| letter | count |
+--------+-------+
| M      |     8 |
| N      |     8 |
+--------+-------+

2、根据“日期-时间”分组

（Recipe 8.15. Date-Based Summaries）

示例--根据 { year-month }分组

mysql> select concat(year(trav_date), '_' , month(trav_date)) as month_group,-> count(*) as month_drivers,-> sum(miles) as month_miles-> from driver_log group by year(trav_date), month(trav_date);
+-------------+---------------+-------------+
| month_group | month_drivers | month_miles |
+-------------+---------------+-------------+
| 2006_8      |             7 |        1388 |
| 2006_9      |             3 |         778 |
+-------------+---------------+-------------+
示例--根据 { year-week }分组 

mysql> select yearweek(trav_date) as week_group,-> count(*) as month_drivers,-> sum(miles) as month_miles-> from driver_log group by week_group;
+------------+---------------+-------------+
| week_group | month_drivers | month_miles |
+------------+---------------+-------------+
|     200634 |             1 |         115 |
|     200635 |             9 |        2051 |
+------------+---------------+-------------+

3、“分组计算” 和 “全局计算” 同时存在查询中

（Recipe 8.16. Working with Per-Group and Overall Summary Values Simultaneously）

示例--将两个查询分开

mysql> select @total := sum(miles) as total_miles from driver_log;
+-------------+
| total_miles |
+-------------+
|        2166 |
+-------------+mysql> select name,-> sum(miles) as 'miles/driver',-> (sum(miles)*100)/@total as 'percent of total miles'-> from driver_log group by name;
+-------+--------------+------------------------+
| name  | miles/driver | percent of total miles |
+-------+--------------+------------------------+
| Ben   |          362 |                16.7128 |
| Henry |          911 |                42.0591 |
| Suzi  |          893 |                41.2281 |
+-------+--------------+------------------------+
示例--合并 

mysql> select name,-> sum(miles) as 'miles/driver',-> (sum(miles)*100)/(select sum(miles) from driver_log) as 'total miles'-> from driver_log group by name;
+-------+--------------+-------------+
| name  | miles/driver | total miles |
+-------+--------------+-------------+
| Ben   |          362 |     16.7128 |
| Henry |          911 |     42.0591 |
| Suzi  |          893 |     41.2281 |
+-------+--------------+-------------+
示例--带条件判断的（having xxx）

( 前两个查询用来演示 )

mysql> select avg(miles) from driver_log;
+------------+
| avg(miles) |
+------------+
|   216.6000 |
+------------+mysql> select name, avg(miles) as driver_avg from driver_log-> group by name;
+-------+------------+
| name  | driver_avg |
+-------+------------+
| Ben   |   120.6667 |
| Henry |   182.2000 |
| Suzi  |   446.5000 |
+-------+------------+mysql> select name, avg(miles) as driver_avg from driver_log-> group by name-> having driver_avg < (select avg(miles) from driver_log);
+-------+------------+
| name  | driver_avg |
+-------+------------+
| Ben   |   120.6667 |
| Henry |   182.2000 |
+-------+------------+

4、删除一行数据，sequence 列会重新生成吗？

答案：不会！

演示如下：

+----+-------------------+------------+------------+
| id | name              | date       | origin     |
+----+-------------------+------------+------------+
|  1 | housefly          | 2006-09-10 | kitchen    |
|  2 | millipede         | 2006-09-10 | driveway   |
|  3 | grasshopper       | 2006-09-10 | front yard |
|  4 | stink bug         | 2006-09-10 | front yard |
|  5 | cabbage butterfly | 2006-09-10 | garden     |
|  6 | ant               | 2006-09-10 | back yard  |
|  7 | ant               | 2006-09-10 | back yard  |
|  8 | millbug           | 2006-09-10 | under rock |
+----+-------------------+------------+------------+
删除 id 为2的行： 

mysql> delete from insect where id=2;
结果： 

mysql> select * from insect;
+----+-------------------+------------+------------+
| id | name              | date       | origin     |
+----+-------------------+------------+------------+
|  1 | housefly          | 2006-09-10 | kitchen    |
|  3 | grasshopper       | 2006-09-10 | front yard |
|  4 | stink bug         | 2006-09-10 | front yard |
|  5 | cabbage butterfly | 2006-09-10 | garden     |
|  6 | ant               | 2006-09-10 | back yard  |
|  7 | ant               | 2006-09-10 | back yard  |
|  8 | millbug           | 2006-09-10 | under rock |
+----+-------------------+------------+------------+

5、sequence 列指定值插入，不是我认为的不能指定值哦！

a、id 重复，报错

b、id 不重复，可以插入！

报错演示：

mysql> insert into insect (id, name, date, origin) values (1,'test','2011-08-25','test');
ERROR 1062 (23000): Duplicate entry '1' for key 1
id 不重复演示——插入比当前sequence 值最大还大的值 

mysql> insert into insect (id, name, date, origin) values (20,'test','2011-08-25','test');
Query OK, 1 row affected (0.03 sec)mysql> select * from insect;
+----+-------------------+------------+------------+
| id | name              | date       | origin     |
+----+-------------------+------------+------------+
|  1 | housefly          | 2006-09-10 | kitchen    |
|  3 | grasshopper       | 2006-09-10 | front yard |
|  4 | stink bug         | 2006-09-10 | front yard |
|  5 | cabbage butterfly | 2006-09-10 | garden     |
|  6 | ant               | 2006-09-10 | back yard  |
|  7 | ant               | 2006-09-10 | back yard  |
|  8 | millbug           | 2006-09-10 | under rock |
| 20 | test              | 2011-08-25 | test       |
+----+-------------------+------------+------------+
id 不重复演示——补上被删除的行（id 为2） 

mysql> insert into insect (id, name, date, origin) values (2,'test','2011-08-25','test');
Query OK, 1 row affected (0.01 sec)mysql> select * from insect;
+----+-------------------+------------+------------+
| id | name              | date       | origin     |
+----+-------------------+------------+------------+
|  1 | housefly          | 2006-09-10 | kitchen    |
|  2 | test              | 2011-08-25 | test       |
|  3 | grasshopper       | 2006-09-10 | front yard |
|  4 | stink bug         | 2006-09-10 | front yard |
|  5 | cabbage butterfly | 2006-09-10 | garden     |
|  6 | ant               | 2006-09-10 | back yard  |
|  7 | ant               | 2006-09-10 | back yard  |
|  8 | millbug           | 2006-09-10 | under rock |
| 20 | test              | 2011-08-25 | test       |
+----+-------------------+------------+------------+

6、删除最大 sequence 行，对以后插入新行 sequence 值的影响

（Recipe 11.3. The Effect of Row Deletions on Sequence Generation）

a、DBD engine，下一个序列值是当前最大序列值加1（例如删掉 id 为20，下次插入即为9）

b、MyISAM or InnoDB  engine，永远不重复（例如删掉 id 为20，下次插入即为21）

查看表的 engine——示例

mysql> select engine from information_schema.tables-> where table_schema = 'cookbook' and table_name = 'insect';
+--------+
| engine |
+--------+
| InnoDB |
+--------+

7、获取序列的值

（Recipe 11.4. Retrieving Sequence Values）

Server-side—— select last_insert_id()示例

mysql> insert into insect(name,date,origin)-> values('testLastInsert', '2011-08-25', 'testLastInsert');
Query OK, 1 row affected (0.03 sec)mysql> select last_insert_id();
+------------------+
| last_insert_id() |
+------------------+
|               21 |
+------------------+
1 row in set (0.00 sec)mysql> select * from insect where id=last_insert_id();
+----+----------------+------------+----------------+
| id | name           | date       | origin         |
+----+----------------+------------+----------------+
| 21 | testLastInsert | 2011-08-25 | testLastInsert |
+----+----------------+------------+----------------+
LAST_INSERT_ID() 能保证在多用户多线程操作下获取的序列值是正确的（即，当前connection 最后插入行的序列值），因为它和底层的connection 关联。

Client-side:

//Statement
Statement s = conn.createStatement ();
s.executeUpdate ("INSERT INTO insect (name,date,origin) VALUES('moth','2006-09-14','windowsill')");
long seq = ((com.mysql.jdbc.Statement) s).getLastInsertID ();
s.close ();//PreparedStatement
PreparedStatement s = conn.prepareStatement ("INSERT INTO insect (name,date,origin) VALUES('moth','2006-09-14','windowsill')");
s.executeUpdate ();
long seq = ((com.mysql.jdbc.PreparedStatement) s).getLastInsertID ();
s.close ();
推荐策略：如果后面需要序列值，则应在插入数据后即获取序列值保存着，以备后用！

8、设定序列的初始值

For MyISAM or InnoDB tables

mysql> CREATE TABLE t-> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id))-> AUTO_INCREMENT = 100;
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> SELECT id FROM t ORDER BY id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+
或 

mysql> CREATE TABLE t-> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id));
mysql> ALTER TABLE t AUTO_INCREMENT = 100;
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> SELECT id FROM t ORDER BY id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+
To start a sequence at n for storage engines other than MyISAM or InnoDB, you can use a trick: insert a "fake" row with sequence value n -1, and then delete it after inserting one or more "real" rows. The following example illustrates how to start a sequence at 100 for a BDB table: 

mysql> CREATE TABLE t-> (id INT UNSIGNED NOT NULL AUTO_INCREMENT, PRIMARY KEY (id))-> ENGINE = BDB;
mysql> INSERT INTO t (id) VALUES(99);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> INSERT INTO t (id) VALUES(NULL);
mysql> DELETE FROM t WHERE id = 99;
mysql> SELECT * FROM t ORDER BY id;
+-----+
| id  |
+-----+
| 100 |
| 101 |
| 102 |
+-----+

9、创建多重序列

（Recipe 11.11. Using an AUTO_INCREMENT Column to Create Multiple Sequences）

注意：只适合 engine 为 MyISAM 和 BDB

创建时注意指定表的 engine，因为我的默认为 InnoDB

DROP TABLE IF EXISTS bug;CREATE TABLE bug
(id      INT UNSIGNED NOT NULL AUTO_INCREMENT,name    VARCHAR(30) NOT NULL, # type of bugdate    DATE NOT NULL,        # date collectedorigin  VARCHAR(30) NOT NULL, # where collectedPRIMARY KEY (name, id)
)engine=myisam;INSERT INTO bug (name,date,origin) VALUES
('ant','2006-10-07','kitchen'),
('millipede','2006-10-07','basement'),
('beetle','2006-10-07','basement'),
('ant','2006-10-07','front yard'),
('ant','2006-10-07','front yard'),
('honeybee','2006-10-08','back yard'),
('cricket','2006-10-08','garage'),
('beetle','2006-10-08','front yard'),
('termite','2006-10-09','kitchen woodwork'),
('cricket','2006-10-10','basement'),
('termite','2006-10-11','bathroom woodwork'),
('honeybee','2006-10-11','garden'),
('cricket','2006-10-11','garden'),
('ant','2006-10-11','garden')
;
限制：

a、AUTO_INCREMENT 列必须是定义索引的最后一个（如：PRIMARY  KEY  (name, id)），主键是强制索引

b、PRIMARY KEY 不允许包含 NULL 列，如果非 ATUO_INCREMENT 列允许NULL，则应该用 UNIQUE 索引

mysql> SELECT * FROM bug ORDER BY name, id;
+----+-----------+------------+-------------------+
| id | name      | date       | origin            |
+----+-----------+------------+-------------------+
|  1 | ant       | 2006-10-07 | kitchen           |
|  2 | ant       | 2006-10-07 | front yard        |
|  3 | ant       | 2006-10-07 | front yard        |
|  4 | ant       | 2006-10-11 | garden            |
|  1 | beetle    | 2006-10-07 | basement          |
|  2 | beetle    | 2006-10-08 | front yard        |
|  1 | cricket   | 2006-10-08 | garage            |
|  2 | cricket   | 2006-10-10 | basement          |
|  3 | cricket   | 2006-10-11 | garden            |
|  1 | honeybee  | 2006-10-08 | back yard         |
|  2 | honeybee  | 2006-10-11 | garden            |
|  1 | millipede | 2006-10-07 | basement          |
|  1 | termite   | 2006-10-09 | kitchen woodwork  |
|  2 | termite   | 2006-10-11 | bathroom woodwork |
+----+-----------+------------+-------------------+
其他示例： 

CREATE TABLE housewares
(category    VARCHAR(3) NOT NULL,serial      INT UNSIGNED NOT NULL AUTO_INCREMENT,country     VARCHAR(2) NOT NULL,description VARCHAR(255),PRIMARY KEY (category, country, serial)
);
或 

mysql> ALTER TABLE housewares-> ADD category VARCHAR(3) NOT NULL FIRST,-> ADD serial INT UNSIGNED NOT NULL AUTO_INCREMENT AFTER category,-> ADD country VARCHAR(2) NOT NULL AFTER serial,-> ADD PRIMARY KEY (category, country, serial);
mysql> UPDATE housewares SET category = LEFT(id,3);
mysql> UPDATE housewares SET serial = MID(id,4,5);
mysql> UPDATE housewares SET country = RIGHT(id,2);
mysql> ALTER TABLE housewares DROP id;
mysql> SELECT * FROM housewares;
+----------+--------+---------+------------------+
| category | serial | country | description      |
+----------+--------+---------+------------------+
| DIN      |  40672 | US      | dining table     |
| KIT      |    372 | UK      | garbage disposal |
| KIT      |   1729 | JP      | microwave oven   |
| BED      |     38 | SG      | bedside lamp     |
| BTH      |    485 | US      | shower stall     |
| BTH      |    415 | JP      | lavatory         |
+----------+--------+---------+------------------+
指定排序 

mysql> SELECT category, serial, country,-> CONCAT(category,LPAD(serial,5,'0'),country) AS id-> FROM housewares ORDER BY category, country, serial;
+----------+--------+---------+------------+
| category | serial | country | id         |
+----------+--------+---------+------------+
| BED      |     38 | SG      | BED00038SG |
| BTH      |    415 | JP      | BTH00415JP |
| BTH      |    485 | US      | BTH00485US |
| DIN      |  40672 | US      | DIN40672US |
| KIT      |   1729 | JP      | KIT01729JP |
| KIT      |    372 | UK      | KIT00372UK |
+----------+--------+---------+------------+
或修改 serial 的宽度为5，然后再直接连接排序 

mysql> ALTER TABLE housewares-> MODIFY serial INT(5) UNSIGNED ZEROFILL NOT NULL AUTO_INCREMENT;
mysql> SELECT category, serial, country,-> CONCAT(category,serial,country) AS id-> FROM housewares ORDER BY category, country, serial;
+----------+--------+---------+------------+
| category | serial | country | id         |
+----------+--------+---------+------------+
| BED      |  00038 | SG      | BED00038SG |
| BTH      |  00415 | JP      | BTH00415JP |
| BTH      |  00485 | US      | BTH00485US |
| DIN      |  40672 | US      | DIN40672US |
| KIT      |  01729 | JP      | KIT01729JP |
| KIT      |  00372 | UK      | KIT00372UK |
+----------+--------+---------+------------+
或些一个存储过程，调用存储过程 

CREATE FUNCTION houseware_id(category VARCHAR(3),serial INT UNSIGNED,country VARCHAR(2))
RETURNS VARCHAR(10) DETERMINISTIC
RETURN CONCAT(category,LPAD(serial,5,'0'),country);

mysql> SELECT category, serial, country,-> houseware_id(category,serial,country) AS id-> FROM housewares;
+----------+--------+---------+------------+
| category | serial | country | id         |
+----------+--------+---------+------------+
| BED      | 38     | SG      | BED00038SG |
| BTH      | 415    | JP      | BTH00415JP |
| BTH      | 485    | US      | BTH00485US |
| DIN      | 40672  | US      | DIN40672US |
| KIT      | 1729   | JP      | KIT01729JP |
| KIT      | 372    | UK      | KIT00372UK |
+----------+--------+---------+------------+

10、使用序列产生计数器

（Recipe 11.14. Using Sequence Generators as Counters）

CREATE TABLE booksales
(title   VARCHAR(60) NOT NULL,   # book titlecopies  INT UNSIGNED NOT NULL,  # number of copies soldPRIMARY KEY (title)
);
a、一般的做法：初始化设置为0，以后更新时加 1。 

INSERT INTO booksales (title,copies) VALUES('The Greater Trumps',0);
UPDATE booksales SET copies = copies+1 WHERE title = 'The Greater Trumps';
b、或使用 INSERT ... ON DUPLICATE KEY UPDATE 语句： 

INSERT INTO booksales (title,copies)VALUES('The Greater Trumps',1)ON DUPLICATE KEY UPDATE copies = copies+1;
获取更新的值： 

SELECT copies FROM booksales WHERE title = 'The Greater Trumps';
缺陷：

在多用户多线程的情况下，用户A 完成更新在取值查询开始前，用户B执行了更新，这样用户A 查询的数据就错误了！
修改：使用LAST_INSERT_ID(expr) 函数，保证数据一致性

INSERT INTO booksales (title,copies)VALUES('The Greater Trumps',LAST_INSERT_ID(1))ON DUPLICATE KEY UPDATE copies = LAST_INSERT_ID(copies+1);
这样每次都执行该语句，第一次是插入操作，以后是更新操作。

获取插入/更新后的值：

Server-side:

SELECT LAST_INSERT_ID();
Client-side: 

Statement s = conn.createStatement ();
s.executeUpdate ("INSERT INTO booksales (title,copies)"+ " VALUES('The Greater Trumps',LAST_INSERT_ID(1))"+ " ON DUPLICATE KEY UPDATE copies = LAST_INSERT_ID(copies+1)");
long count = ((com.mysql.jdbc.Statement) s).getLastInsertID ();
s.close ();





















































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