SQL必知必會 14-22（完），sql必知14-22

SQL必知必會 14-22（完），sql必知14-22

博主依然不想打字，又向你仍來了一堆代碼。。。

13（續）

在SELECT中用COUNT（）以及聯合

mysql> SELECT customers.cust_id,COUNT(orders.order_num) AS num_ord
    -> FROM customers INNER JOIN orders
    ->  ON customers.cust_id=orders.cust_id
    -> GROUP BY cust_id;
+------------+---------+
| cust_id    | num_ord |
+------------+---------+
| 1000000001 |       2 |
| 1000000003 |       1 |
| 1000000004 |       1 |
| 1000000005 |       1 |
+------------+---------+
4 rows in set (0.00 sec)

14、組合查詢

UNION，UNION ALL（顯示重復行）；

多條SELECT合並為一個查詢輸出；

必須有相同的列數，順序可以不一樣但數據類型要可以轉換的；

UNION ALL顯示重復行，除此以外的使用，都可以用WHERE來替換；

ORDER BY放在最後一句，只需要一句；

不過事實證明，順序還是會有影響的 。。。

mysql> SELECT cust_name,cust_contact,cust_emali
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI');
ERROR 1054 (42S22): Unknown column 'cust_emali' in 'field list'
mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI');
+---------------+--------------+-----------------------+
| cust_name     | cust_contact | cust_email            |
+---------------+--------------+-----------------------+
| Village Toys  | John Smith   | sales@villagetoys.com |
| Fun4All       | Jim Jones    | jjones@fun4all.com    |
| The Toy Store | Kim Howard   | NULL                  |
+---------------+--------------+-----------------------+
3 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_email,cust_contact
    -> FROM customers
    -> WHERE cust_name='Fun4All';
+-----------+-----------------------+--------------------+
| cust_name | cust_email            | cust_contact       |
+-----------+-----------------------+--------------------+
| Fun4All   | jjones@fun4all.com    | Jim Jones          |
| Fun4All   | dstephens@fun4all.com | Denise L. Stephens |
+-----------+-----------------------+--------------------+
2 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI')
    -> UNION
    -> SELECT cust_name,cust_email,cust_contact
    -> FROM customers
    -> WHERE cust_name='Fun4All';
+---------------+-----------------------+-----------------------+
| cust_name     | cust_contact          | cust_email            |
+---------------+-----------------------+-----------------------+
| Village Toys  | John Smith            | sales@villagetoys.com |
| Fun4All       | Jim Jones             | jjones@fun4all.com    |
| The Toy Store | Kim Howard            | NULL                  |
| Fun4All       | jjones@fun4all.com    | Jim Jones             |
| Fun4All       | dstephens@fun4all.com | Denise L. Stephens    |
+---------------+-----------------------+-----------------------+
5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI')
    -> UNION
    -> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_name='Fun4All';
+---------------+--------------------+-----------------------+
| cust_name     | cust_contact       | cust_email            |
+---------------+--------------------+-----------------------+
| Village Toys  | John Smith         | sales@villagetoys.com |
| Fun4All       | Jim Jones          | jjones@fun4all.com    |
| The Toy Store | Kim Howard         | NULL                  |
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
+---------------+--------------------+-----------------------+
4 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI')
    -> UNION ALL
    -> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_name='Fun4All';
+---------------+--------------------+-----------------------+
| cust_name     | cust_contact       | cust_email            |
+---------------+--------------------+-----------------------+
| Village Toys  | John Smith         | sales@villagetoys.com |
| Fun4All       | Jim Jones          | jjones@fun4all.com    |
| The Toy Store | Kim Howard         | NULL                  |
| Fun4All       | Jim Jones          | jjones@fun4all.com    |
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
+---------------+--------------------+-----------------------+
5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_state IN ('IL','IN','MI')
    -> UNION
    -> SELECT cust_name,cust_contact,cust_email
    -> FROM customers
    -> WHERE cust_name='Fun4All'
    -> ORDER BY cust_name;
+---------------+--------------------+-----------------------+
| cust_name     | cust_contact       | cust_email            |
+---------------+--------------------+-----------------------+
| Fun4All       | Jim Jones          | jjones@fun4all.com    |
| Fun4All       | Denise L. Stephens | dstephens@fun4all.com |
| The Toy Store | Kim Howard         | NULL                  |
| Village Toys  | John Smith         | sales@villagetoys.com |
+---------------+--------------------+-----------------------+
4 rows in set (0.00 sec)

15、插入數據

INSERT,INSERT INTO,INSERT SELECT,SELECT INTO

插入完整的行，插入行的一部分，插入某些查詢結果；

用INSERT INTO替代INSERT，提高可移植性；

注意格式寫法；

最好寫上列名；

INSERT一般只能插入一條，INSERT SELECT是個例外；

SELECT INTO實現復制（MySQL和Oracle的有所不同）

mysql> CREATE TABLE custNew(
    -> cust_id INT PRIMARY KEY,
    -> cust_contact VARCHAR(32),
    -> cust_email VARCHAR(32),
    -> cust_name VARCHAR(32),
    -> cust_address VARCHAR(64),
    -> cust_city VARCHAR(16),
    -> cust_state VARCHAR(16),
    -> cust_zip SMALLINT,
    -> cust_country VARCHAR(16)
    -> );
Query OK, 0 rows affected (0.21 sec)

mysql> INSERT INTO custNew(
    ->   cust_id,
    ->   cust_email,
    ->   cust_name,
    ->   cust_zip,
    ->   cust_country,
    ->   cust_city)
    -> VALUES(
    ->   1021,
    ->   'liangbocv@126.com',
    ->   'Andy Liang',
    ->   610000,
    ->   'China',
    ->   'Chengdu');
Query OK, 1 row affected, 1 warning (0.04 sec)

mysql> INSERT INTO customers(
    ->   cust_id,
    ->   cust_email,
    ->   cust_name,
    ->   cust_zip,
    ->   cust_country,
    ->   cust_city)
    -> SELECT cust_id,
    ->   cust_email,
    ->   cust_name,
    ->   cust_zip,
    ->   cust_country,
    ->   cust_city
    -> FROM custNew;
Query OK, 1 row affected (0.03 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM customers;
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |
| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |
| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |
| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |
| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |
| 1021       | Andy Liang    | NULL                 | Chengdu   | NULL       | 32767    | China        | NULL               | liangbocv@126.com     |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
6 rows in set (0.00 sec)

mysql> CREATE TABLE custcopy(
    -> cust_id VARCHAR(16),
    -> cust_contact VARCHAR(32),
    -> cust_email VARCHAR(32),
    -> cust_name VARCHAR(32),
    -> cust_address VARCHAR(64),
    -> cust_city VARCHAR(16),
    -> cust_state VARCHAR(16),
    -> cust_zip VARCHAR(16),
    -> cust_country VARCHAR(16)
    -> );
Query OK, 0 rows affected (0.26 sec)

mysql> SELECT *
    -> INTO custcopy
    -> FROM customers;
ERROR 1327 (42000): Undeclared variable: custcopy
mysql> CREATE TABLE custcopy2 AS
    -> SELECT *
    -> FROM customers;
Query OK, 6 rows affected (0.41 sec)
Records: 6  Duplicates: 0  Warnings: 0

16、更新和刪除數據

UPADTE,DELETE

容易使用，但請小心使用；（沒有UNDO！！！）

UPDATE為null=DELETE；

一些習慣：一定帶WHERE ,避免對整個表有影響；

  對數據做更改時，請先SELECT查詢一下，看對象是否沒錯；

  確保每個表有主鍵

mysql> SELECT cust_id,cust_address,cust_state
    -> FROM customers
    -> WHERE cust_id='1021';
+---------+--------------+------------+
| cust_id | cust_address | cust_state |
+---------+--------------+------------+
| 1021    | NULL         | NULL       |
+---------+--------------+------------+
1 row in set (0.00 sec)

mysql> UPDATE customers
    -> SET cust_address='2006 Xiyuan Ave.',
    ->     cust_state='SC'
    -> WHERE cust_id='1021';
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT cust_id,cust_address,cust_state
    -> FROM customers
    -> WHERE cust_id='1021';
+---------+------------------+------------+
| cust_id | cust_address     | cust_state |
+---------+------------------+------------+
| 1021    | 2006 Xiyuan Ave. | SC         |
+---------+------------------+------------+
1 row in set (0.00 sec)

mysql> UPDATE customers
    -> SET cust_email=NULL
    -> WHERE cust_id='1021';
Query OK, 1 row affected (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> DELETE FROM customers
    -> WHERE cust_id='1021';
Query OK, 1 row affected (0.08 sec)

17、創建和操作表

CREATE,DROP,ALTER,RENAME,DEFAULT

更新表，和更新數據一樣小心，做好備份；

重命名不太一樣，mysql是RENAME

mysql> ALTER TABLE custcopy2
    -> ADD cust_gender VARCHAR(8);
Query OK, 0 rows affected (0.41 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> SELECT CURRENT_DATE();
+----------------+
| CURRENT_DATE() |
+----------------+
| 2016-08-10     |
+----------------+
1 row in set (0.16 sec)

mysql> ALTER TABLE custcopy2
    -> ADD add_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP;
Query OK, 0 rows affected (0.46 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DROP TABLE custcopy;
Query OK, 0 rows affected (0.13 sec)

mysql> RENAME TABLE custcopy2 TO custcopy;
Query OK, 0 rows affected (0.10 sec)

18、使用視圖

VIEW

view實際上就是個虛擬的表，只包含使用時動態檢索數據的查詢；

使用view，有利於代碼重用，保護數據，簡化操作；

視圖名也要唯一；可以嵌套，一般禁止ORDER BY；

用於簡化復雜聯結，格式化輸出，過濾不想要的數據等；

WHERE語句會自動合並

mysql> CREATE VIEW shit AS
    -> SELECT cust_name,cust_id,cust_contact,cust_address
    -> FROM customers
    -> ;
Query OK, 0 rows affected (0.07 sec)

mysql> SELECT cust_name,cust_address
    -> FROM shit
    -> WHERE cust_id='1021';
Empty set (0.00 sec)

mysql> SELECT * FROM customers;
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |
| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |
| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |
| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |
| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
5 rows in set (0.00 sec)

mysql> SELECT cust_name,cust_address
    -> FROM shit
    -> WHERE cust_id='1000000001';
+--------------+----------------+
| cust_name    | cust_address   |
+--------------+----------------+
| Village Toys | 200 Maple Lane |
+--------------+----------------+
1 row in set (0.00 sec)

mysql> CREATE VIEW hasEmail AS
    -> SELECT cust_name,cust_id,cust_email
    -> FROM customers
    -> WHERE cust_email IS NOT NULL;
Query OK, 0 rows affected (0.06 sec)

mysql> SELECT *
    -> FROM hasEmail
    -> WHERE cust_name='Fun4All';
+-----------+------------+-----------------------+
| cust_name | cust_id    | cust_email            |
+-----------+------------+-----------------------+
| Fun4All   | 1000000003 | jjones@fun4all.com    |
| Fun4All   | 1000000004 | dstephens@fun4all.com |
+-----------+------------+-----------------------+
2 rows in set (0.00 sec)

19、存儲過程

PROCEDURE,DELIMITER,CALL

以下引用自百度：存儲過程（Stored Procedure）是在大型數據庫系統中，一組為了完成特定功能的SQL 語句集，存儲在數據庫中，經過第一次編譯後再次調用不需要再次編譯，用戶通過指定存儲過程的名字並給出參數（如果該存儲過程帶有參數）來執行它。存儲過程是數據庫中的一個重要對象，任何一個設計良好的數據庫應用程序都應該用到存儲過程。

有點好玩又有點繁瑣的。。。

mysql> DELIMITER &&
mysql> CREATE PROCEDURE showAll()
    ->   BEGIN
    ->   SELECT * FROM customers;
    -> END &&
Query OK, 0 rows affected (0.04 sec)

mysql> CALL showAll();
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| cust_id    | cust_name     | cust_address         | cust_city | cust_state | cust_zip | cust_country | cust_contact       | cust_email            |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
| 1000000001 | Village Toys  | 200 Maple Lane       | Detroit   | MI         | 44444    | USA          | John Smith         | sales@villagetoys.com |
| 1000000002 | Kids Place    | 333 South Lake Drive | Columbus  | OH         | 43333    | USA          | Michelle Green     | NULL                  |
| 1000000003 | Fun4All       | 1 Sunny Place        | Muncie    | IN         | 42222    | USA          | Jim Jones          | jjones@fun4all.com    |
| 1000000004 | Fun4All       | 829 Riverside Drive  | Phoenix   | AZ         | 88888    | USA          | Denise L. Stephens | dstephens@fun4all.com |
| 1000000005 | The Toy Store | 4545 53rd Street     | Chicago   | IL         | 54545    | USA          | Kim Howard         | NULL                  |
+------------+---------------+----------------------+-----------+------------+----------+--------------+--------------------+-----------------------+
5 rows in set (0.00 sec)

Query OK, 0 rows affected (0.08 sec)

mysql> DELIMITER $
mysql> CREATE PROCEDURE getID(
    ->   IN id VARCHAR(32))
    ->   BEGIN
    ->   SELECT *
    ->   FROM customers
    ->   WHERE cust_id=id;
    -> END $
Query OK, 0 rows affected (0.00 sec)

mysql> CALL getID('1000000001')$
+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+
| cust_id    | cust_name    | cust_address   | cust_city | cust_state | cust_zip | cust_country | cust_contact | cust_email            |
+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+
| 1000000001 | Village Toys | 200 Maple Lane | Detroit   | MI         | 44444    | USA          | John Smith   | sales@villagetoys.com |
+------------+--------------+----------------+-----------+------------+----------+--------------+--------------+-----------------------+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.03 sec)

mysql> DELIMITER ;

注意輸入參數那裡的變化。

20、事務管理

TRANSACTION,COMMIT,ROLLBACK,SAVEPOINT

用來維護數據庫的完整性，保證成批的SQL操作要麼完全執行，要麼完全不執行；

保留點越多越好，更好的是形成習慣~

mysql> BEGIN;
Query OK, 0 rows affected (0.00 sec)

mysql> SAVEPOINT begin;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO customers(cust_name,cust_country)
    ->  VALUES('Andy Liang','China');
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> ROLLBACK TO begin;
Query OK, 0 rows affected (0.04 sec)

mysql> COMMIT;
Query OK, 0 rows affected (0.00 sec)

MySQL是一步步來的，就是慢慢監督的一樣。

21、使用游標

CURSOR

略。。。。（老子做web不想用游標，你來打我啊

22、約束，索引，觸發器

約束:

PRIMARY KEY,UNIQUE,REFERENCES,ALTER,CONSTRAINT,CHECK

主鍵：值互異，NOT NULL，不修改/更新，不重用，每個表僅能有一個主鍵，可以用來定義外鍵（舉例：id

唯一：值互異，可以有NULL，可修改/更新，可重用，可有多個唯一鍵，不能用來定義外鍵

外鍵：兩個表，確定子表某一列的合法性

檢查約束：CHECK，靈活約束

mysql> CREATE TABLE test(
    -> id SMALLINT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    -> socialid VARCHAR(64) UNIQUE,
    -> cust_id VARCHAR(16) NOT NULL REFERENCES customers(cust_id),
    -> quantity SMALLINT CHECK (quantity>0),
    -> gender VARCHAR(8) CHECK (gender LIKE '[MF]')
    -> );
Query OK, 0 rows affected (0.20 sec)

另外，用ALTER語句再對表進行更改操作

ALTER TABLE test
ADD CONSTRAINT PRIMARY KEY (cust_id);

ALTER TABLE test
ADD CONSTRAINT UNIQUE KEY (id);

ALTER TABLE test
ADD CONSTRAINT 
FOREIGN KEY (cust_id) REFERENCES customers (cust_id);

ALTER TABLE test
ADD CONSTRAINT CHECK (quantity<1000);

索引：

INDEX

搜索某些列的效率提高；

請動態的創建索引——數據庫在不斷更新，索引效率在變化；索引效率提升的代價是插入等操作性能的犧牲；大量空間的使用；

mysql> CREATE INDEX prod_name_id
    -> ON PRODUCTS (prod_name);
Query OK, 0 rows affected (0.31 sec)
Records: 0  Duplicates: 0  Warnings: 0

觸發器：

TRIGGER

在特定的數據庫活動發生時自動執行；

一般用途：保證數據一致（全大寫等），聯動（log的記錄）等；

約束要比觸發器快，盡量用約束；

完！！（對，這裡又滅有代碼了