子查询 和 递增

=》子查询或内部查询或嵌套查询在另一个SQL查询的查询和嵌入式WHERE子句中。
=》子查询用于返回将被用于在主查询作为条件的数据，以进一步限制要检索的数据。
=》子查询可以在SELECT，INSERT，UPDATE使用，而且随着运算符如DELETE语句 =, <, >, >=, <=, IN, BETWEEN 等.

子查询最频繁使用的SELECT语句。其基本语法如下：
SELECT column_name [, column_name ]FROM table1 [, table2 ]
WHERE column_name OPERATOR
(SELECT column_name [, column_name ] FROM table1 [, table2 ] [WHERE])
#例子
SQL> SELECT * FROM CUSTOMERS WHERE ID IN
(SELECT ID FROM CUSTOMERS WHERE SALARY > 4500) ;

INSERT INTO table_name [ (column1 [, column2 ]) ] 
SELECT [ *|column1 [, column2 ] FROM table1 [, table2 ] [ WHERE VALUE OPERATOR ]
#例子
SQL> INSERT INTO CUSTOMERS_BKP 
SELECT * FROM CUSTOMERS 
WHERE ID IN (SELECT ID FROM CUSTOMERS) ;

UPDATE table
SET column_name = new_value
[ WHERE OPERATOR [ VALUE ]
   (SELECT COLUMN_NAME
   FROM TABLE_NAME)
   [ WHERE) ]
#例子
SQL> UPDATE CUSTOMERS
     SET SALARY = SALARY * 0.25
     WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP
                   WHERE AGE >= 27 );

DELETE FROM TABLE_NAME
[ WHERE OPERATOR [ VALUE ]
   (SELECT COLUMN_NAME
   FROM TABLE_NAME)
   [ WHERE) ]
#例子
SQL> DELETE FROM CUSTOMERS
     WHERE AGE IN (SELECT AGE FROM CUSTOMERS_BKP
                   WHERE AGE > 27 );

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递增

使用自动递增(AUTO_INCREMENT)列：
在MySQL中最简单的方法来使用顺序是定义一个列AUTOINCREMENT并保留其余的事情由MySQL处理。

mysql> CREATE TABLE INSECT
    -> (
    -> id INT UNSIGNED NOT NULL AUTO_INCREMENT,
    -> PRIMARY KEY (id),
    -> name VARCHAR(30) NOT NULL, # type of insect
    -> date DATE NOT NULL, # date collected
    -> origin VARCHAR(30) NOT NULL # where collected
);
Query OK, 0 rows affected (0.02 sec)
mysql> INSERT INTO INSECT (id,name,date,origin) VALUES
    -> (NULL,'housefly','2001-09-10','kitchen'),
    -> (NULL,'millipede','2001-09-10','driveway'),
    -> (NULL,'grasshopper','2001-09-10','front yard');
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> SELECT * FROM INSECT ORDER BY id;
+----+-------------+------------+------------+
| id | name        | date       | origin     |
+----+-------------+------------+------------+
|  1 | housefly    | 2001-09-10 | kitchen    |
|  2 | millipede   | 2001-09-10 | driveway   |
|  3 | grasshopper | 2001-09-10 | front yard |
+----+-------------+------------+------------+
3 rows in set (0.00 sec)

设置初始序列

mysql> CREATE TABLE INSECT
    -> (
    -> id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100,
    -> PRIMARY KEY (id),
    -> name VARCHAR(30) NOT NULL, # type of insect
    -> date DATE NOT NULL, # date collected
    -> origin VARCHAR(30) NOT NULL # where collected
);
#或者
mysql> ALTER TABLE t AUTO_INCREMENT = 100;

重编一个现有的序列：

有可能出现一种情况，当从表中已删除多条记录，并且希望所有的记录重新排序。这可以通过使用一个简单的技巧来完成，但这样做要非常小心，如果你的表连接使用其他表。

如果确定重新排序AUTO_INCREMENT列是不可避免的，这样做的方式是从表中删除列，然后重新添加这个删除的列。下面的例子演示了如何使用这种技术在 insect 表重新编号ID值：

mysql> ALTER TABLE INSECT DROP id;
mysql> ALTER TABLE insect
    -> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST,
    -> ADD PRIMARY KEY (id);