mysql 學習記錄（十七）--水平拆分表、垂直拆分表、中間表
阿新 • • 發佈：2019-02-18
一、理論：
1.垂直拆分表：把主碼某些列放在一個表，把主碼及另外的列放在另一個表中。優點是查詢時可以減少I/O次數，缺點是查詢時需要聯合操作。
2.水平拆分：根據一列或多列的值把資料行放到多個表中。
3.水平拆分表的使用情況：
a.表很大，分割後可以降低在查詢時需要讀的資料和索引頁數以及層數，可提高查詢速度。
b.表中的資料有邏輯上的獨立性。如：不同時期的資料或明顯具有不同使用頻率的資料。
c.需要把資料放在多個介質上。
4.反規範的優勢：
a.增加冗餘列：在多個表中具有相同列，可以在查詢時避免連線操作
b.增加派生列：增加來自於其他表中來自於經過計算的資料，目的是可以減少連線操作以及集函式
c.重新組表：如果許多使用者需要檢視兩個表連接出來的結果資料，則把這兩個表重新組成一個表來減少連線
d.分割表
5.保證資料完整性的技術：
a.批處理維護
b.使用應用邏輯來實現（但此方法不易於維護）
c.使用觸發器
6.中間表的優點：
a.中間表複製源表部分資料並與源表隔離，在中間表中的統計查詢不會對線上應用產生負面應用
b.中間表上可以靈活地新增索引或增加臨時用的新欄位，可提高統計查詢效率和輔助統計查詢
二、實踐：
mysql> CREATE TABLE duck_cust( -> cust_num MEDIUMINT AUTO_INCREMENT, -> cust_title TINYINT , -> cust_last char(20) NOT NULL , -> cust_first char(15) NOT NULL, -> cust_suffix enum('jr.','II','III','IV','v','m.d.','phd.'), -> cust_add1 char(30) NOT NULL, -> cust_add2 char(10) , -> cust_city char(18) NOT NULL, -> cust_state char(2) NOT NULL, -> cust_zip1 char(5) NOT NULL, -> cust_zip2 char(4) , -> cust_duckname char(25) NOT NULL, -> cust_duckbday DATE, -> PRIMARY KEY (cust_num) -> ) engine =MyISAM; Query OK, 0 rows affected (0.02 sec) mysql> insert into duck_cust values -> (null,1,'IrishLoad','red','III','地址1','a302','sea','wa','1111','11111',etrek','2917:10:21'); Query OK, 1 row affected, 2 warnings (0.00 sec) mysql> insert into duck_cust values -> (null,2,'IrishLoad2','red2','III2','地址12','a3022','sea2','wa2','11112',2323422','Netrek2','2927:10:21'); Query OK, 1 row affected, 4 warnings (0.00 sec) mysql> insert into duck_cust values -> (null,3,'IrishLoad3','red3','III3','地址13','a3023','sea3','wa3','11113',232343','Netrek3','2937:10:21'); Query OK, 1 row affected, 4 warnings (0.00 sec) mysql> insert into duck_cust values -> (null,4,'IrishLoad4','red4','III4','地址14','a3024','sea4','wa4','11114',232344','Netrek4','2947:10:21'); Query OK, 1 row affected, 4 warnings (0.01 sec) mysql> insert into duck_cust values -> (null,5,'IrishLoad5','red5','III5','地址15','a3025','sea5','wa5','11115',232345','Netrek5','2957:10:21'); Query OK, 1 row affected, 4 warnings (0.00 sec) mysql> insert into duck_cust values -> (null,6,'IrishLoad6','red6','III6','地址16','a3026','sea6','wa6','11116',232346','Netrek6','2967:10:21'); Query OK, 1 row affected, 4 warnings (0.00 sec) mysql> insert into duck_cust values -> (null,7,'IrishLoad7','red7','III7','地址17','a3027','sea7','wa7','11117',232347','Netrek7','2977:1'); Query OK, 1 row affected, 5 warnings (0.00 sec) mysql> select * from duck_cust procedure analyse() \G; *************************** 1. row *************************** Field_name: sakila.duck_cust.cust_num Min_value: 1 Max_value: 7 Min_length: 1 Max_length: 1 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 4.0000 Std: 2.0000 Optimal_fieldtype: ENUM('1','2','3','4','5','6','7') NOT NULL *************************** 2. row *************************** Field_name: sakila.duck_cust.cust_title Min_value: 1 Max_value: 7 Min_length: 1 Max_length: 1 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 4.0000 Std: 2.0000 Optimal_fieldtype: ENUM('1','2','3','4','5','6','7') NOT NULL *************************** 3. row *************************** Field_name: sakila.duck_cust.cust_last Min_value: IrishLoad Max_value: IrishLoad7 Min_length: 9 Max_length: 10 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 9.8571 Std: NULL Optimal_fieldtype: ENUM('IrishLoad','IrishLoad2','IrishLoad3','IrishLoad4','IrishLoad5','IrishLoad6','IrishLoad7') NOT NULL *************************** 4. row *************************** Field_name: sakila.duck_cust.cust_first Min_value: red Max_value: red7 Min_length: 3 Max_length: 4 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 3.8571 Std: NULL Optimal_fieldtype: ENUM('red','red2','red3','red4','red5','red6','red7') NOT NULL *************************** 5. row *************************** Field_name: sakila.duck_cust.cust_suffix Min_value: III Max_value: III Min_length: 3 Max_length: 3 Empties_or_zeros: 6 Nulls: 0 Avg_value_or_avg_length: 0.4286 Std: NULL Optimal_fieldtype: ENUM('','III') NOT NULL *************************** 6. row *************************** Field_name: sakila.duck_cust.cust_add1 Min_value: Max_value: Min_length: 0 Max_length: 0 Empties_or_zeros: 7 Nulls: 0 Avg_value_or_avg_length: 0.0000 Std: NULL Optimal_fieldtype: CHAR(0) NOT NULL *************************** 7. row *************************** Field_name: sakila.duck_cust.cust_add2 Min_value: a302 Max_value: a3027 Min_length: 4 Max_length: 5 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 4.8571 Std: NULL Optimal_fieldtype: ENUM('a302','a3022','a3023','a3024','a3025','a3026','a3027') NOT NULL *************************** 8. row *************************** Field_name: sakila.duck_cust.cust_city Min_value: sea Max_value: sea7 Min_length: 3 Max_length: 4 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 3.8571 Std: NULL Optimal_fieldtype: ENUM('sea','sea2','sea3','sea4','sea5','sea6','sea7') NOT NULL *************************** 9. row *************************** Field_name: sakila.duck_cust.cust_state Min_value: wa Max_value: wa Min_length: 2 Max_length: 2 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 2.0000 Std: NULL Optimal_fieldtype: ENUM('wa') NOT NULL *************************** 10. row *************************** Field_name: sakila.duck_cust.cust_zip1 Min_value: 1111 Max_value: 11117 Min_length: 4 Max_length: 5 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 4.8571 Std: NULL Optimal_fieldtype: ENUM('1111','11112','11113','11114','11115','11116','11117') NOT NULL *************************** 11. row *************************** Field_name: sakila.duck_cust.cust_zip2 Min_value: 1111 Max_value: 2232 Min_length: 4 Max_length: 4 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 4.0000 Std: NULL Optimal_fieldtype: ENUM('1111','2232') NOT NULL *************************** 12. row *************************** Field_name: sakila.duck_cust.cust_duckname Min_value: Netrek Max_value: Netrek7 Min_length: 6 Max_length: 7 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 6.8571 Std: NULL Optimal_fieldtype: ENUM('Netrek','Netrek2','Netrek3','Netrek4','Netrek5','Netrek6','Netrek7') NOT NULL *************************** 13. row *************************** Field_name: sakila.duck_cust.cust_duckbday Min_value: 0000-00-00 Max_value: 2967-10-21 Min_length: 10 Max_length: 10 Empties_or_zeros: 0 Nulls: 0 Avg_value_or_avg_length: 10.0000 Std: NULL Optimal_fieldtype: ENUM('0000-00-00','2917-10-21','2927-10-21','2937-10-21','2947-10-21','2957-10-21','2967-10-21') NOT NULL 13 rows in set (0.01 sec) ERROR: No query specified mysql> alter table duck_cust modify cust_num mediumint(2); Query OK, 7 rows affected (0.02 sec) Records: 7 Duplicates: 0 Warnings: 0 mysql> create table session( -> cust_id varchar(10), -> cust_amount decimal(16,2) -> , -> cust_date DATE, -> cust_ip varchar(20) -> ); Query OK, 0 rows affected (0.05 sec) mysql> insert into session values (2,3.22,adddate(now(),-2),'192.168.0.2'); e(now(),-15),'192.168.0.15'); insert into session values (16,3.36,adddate(now(),-16),'192.168.0.16');Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (3,3.23,adddate(now(),-3),'192.168.0.3'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (4,3.24,adddate(now(),-4),'192.168.0.4'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (5,3.25,adddate(now(),-5),'192.168.0.5'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (6,3.26,adddate(now(),-6),'192.168.0.6'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (7,3.27,adddate(now(),-7),'192.168.0.7'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (8,3.28,adddate(now(),-8),'192.168.0.8'); Query OK, 1 row affected, 1 warning (0.01 sec) mysql> insert into session values (9,3.29,adddate(now(),-9),'192.168.0.9'); Query OK, 1 row affected, 1 warning (0.01 sec) mysql> insert into session values (10,3.30,adddate(now(),-10),'192.168.0.10'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (11,3.31,adddate(now(),-11),'192.168.0.11'); Query OK, 1 row affected, 1 warning (0.01 sec) mysql> insert into session values (12,3.32,adddate(now(),-12),'192.168.0.12'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (13,3.33,adddate(now(),-13),'192.168.0.13'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (14,3.34,adddate(now(),-14),'192.168.0.14'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (15,3.35,adddate(now(),-15),'192.168.0.15'); Query OK, 1 row affected, 1 warning (0.00 sec) mysql> insert into session values (16,3.36,adddate(now(),-16),'192.168.0.16'); Query OK, 1 row affected, 1 warning (0.01 sec) mysql> create table tmp_session( -> cust_id varchar(10), -> cust_amount decimal(16,2) , -> cust_date DATE, -> cust_ip varchar(20) -> ); Query OK, 0 rows affected (0.03 sec) mysql> select sum(cust_amount) from session -> where cust_date > adddate(now(),-7); +------------------+ | sum(cust_amount) | +------------------+ | 19.41 | +------------------+ 1 row in set (0.02 sec) mysql> insert into tmp_session -> -> select sum(cust_amount) from session -> where cust_date > adddate(now(),-7); ERROR 1136 (21S01): Column count doesn't match value count at row 1 mysql> mysql> insert into tmp_session -> select * from session -> where cust_date > adddate(now(),-7); Query OK, 6 rows affected (0.01 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> select sum(cust_amount) from tmp_session; +------------------+ | sum(cust_amount) | +------------------+ | 19.41 | +------------------+ 1 row in set (0.00 sec)