Using AUTO_INCREMENT——mysql5.5获取自动生成ID的官方文档

http://dev.mysql.com/doc/refman/5.5/en/example-auto-increment.html 写道

 可以使用  LAST_INSERT_ID()SQL函数或者 mysql_insert_id() C API 函数来获得最新插入的ID，这获取的ID是当前connection内的变量，即不会与其他连接插入的ID冲突，因此，不用担心并发插入导致的ID错误。

另外需要注意：mysql_init()函数的初始化必须线程同步，多线程下mysql_init可能会失败core的。

 

 3.6.9 Using AUTO_INCREMENT

The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows:

CREATE TABLE animals (
     id MEDIUMINT NOT NULL AUTO_INCREMENT,
     name CHAR(30) NOT NULL,
     PRIMARY KEY (id)
);

INSERT INTO animals (name) VALUES
    ('dog'),('cat'),('penguin'),
    ('lax'),('whale'),('ostrich');

SELECT * FROM animals;

Which returns:

+----+---------+
| id | name    |
+----+---------+
|  1 | dog     |
|  2 | cat     |
|  3 | penguin |
|  4 | lax     |
|  5 | whale   |
|  6 | ostrich |
+----+---------+

No value was specified for the AUTO_INCREMENT column, so MySQL assigned sequence numbers automatically. You can also explicitly assign 0 to the column to generate sequence numbers. If the column is declared NOT NULL, it is also possible to assign NULL to the column to generate sequence numbers.

You can retrieve the most recent AUTO_INCREMENT value with the LAST_INSERT_ID() SQL function or themysql_insert_id() C API function. These functions are connection-specific, so their return values are not affected by another connection which is also performing inserts.

Use the smallest integer data type for the AUTO_INCREMENT column that is large enough to hold the maximum sequence value you will need. When the column reaches the upper limit of the data type, the next attempt to generate a sequence number fails. Use the UNSIGNED attribute if possible to allow a greater range. For example, if you use TINYINT, the maximum permissible sequence number is 127. For TINYINT UNSIGNED, the maximum is 255. See Section 11.2.1, “Integer Types (Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT” for the ranges of all the integer types.

Note

For a multiple-row insert, LAST_INSERT_ID() and mysql_insert_id() actually return the AUTO_INCREMENT key from the first of the inserted rows. This enables multiple-row inserts to be reproduced correctly on other servers in a replication setup.

To start with an AUTO_INCREMENT value other than 1, set that value with CREATE TABLE or ALTER TABLE, like this:

mysql> ALTER TABLE tbl AUTO_INCREMENT = 100;

InnoDB Notes

For InnoDB tables, be careful if you modify the column containing the auto-increment value in the middle of a sequence of INSERT statements. For example, if you use an UPDATE statement to put a new, larger value in the auto-increment column, a subsequent INSERT could encounter a “Duplicate entry” error. The test whether an auto-increment value is already present occurs if you do a DELETE followed by more INSERT statements, or when you COMMIT the transaction, but not after an UPDATE statement.

MyISAM Notes

• For MyISAM tables, you can specify AUTO_INCREMENT on a secondary column in a multiple-column index. In this case, the generated value for the AUTO_INCREMENT column is calculated as MAX(auto_increment_column) + 1 WHERE prefix=given-prefix. This is useful when you want to put data into ordered groups.

  CREATE TABLE animals (
      grp ENUM('fish','mammal','bird') NOT NULL,
      id MEDIUMINT NOT NULL AUTO_INCREMENT,
      name CHAR(30) NOT NULL,
      PRIMARY KEY (grp,id)
  ) ENGINE=MyISAM;
  
  INSERT INTO animals (grp,name) VALUES
      ('mammal','dog'),('mammal','cat'),
      ('bird','penguin'),('fish','lax'),('mammal','whale'),
      ('bird','ostrich');
  
  SELECT * FROM animals ORDER BY grp,id;
  

  Which returns:

  +--------+----+---------+
  | grp    | id | name    |
  +--------+----+---------+
  | fish   |  1 | lax     |
  | mammal |  1 | dog     |
  | mammal |  2 | cat     |
  | mammal |  3 | whale   |
  | bird   |  1 | penguin |
  | bird   |  2 | ostrich |
  +--------+----+---------+
  

  In this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values are reused if you delete the row with the biggest AUTO_INCREMENT value in any group. This happens even for MyISAMtables, for which AUTO_INCREMENT values normally are not reused.

• If the AUTO_INCREMENT column is part of multiple indexes, MySQL generates sequence values using the index that begins with the AUTO_INCREMENT column, if there is one. For example, if the animals table contained indexes PRIMARY KEY (grp, id) and INDEX (id), MySQL would ignore the PRIMARY KEY for generating sequence values. As a result, the table would contain a single sequence, not a sequence per grp value.

Further Reading

More information about AUTO_INCREMENT is available here:

• How to assign the AUTO_INCREMENT attribute to a column: Section 13.1.17, “CREATE TABLE Syntax”, andSection 13.1.7, “ALTER TABLE Syntax”.

• How AUTO_INCREMENT behaves depending on the NO_AUTO_VALUE_ON_ZERO SQL mode: Section 5.1.7, “Server SQL Modes”.

• How to use the LAST_INSERT_ID() function to find the row that contains the most recent AUTO_INCREMENTvalue: Section 12.14, “Information Functions”.

• Setting the AUTO_INCREMENT value to be used: Section 5.1.4, “Server System Variables”.

• AUTO_INCREMENT and replication: Section 17.4.1.1, “Replication and AUTO_INCREMENT”.

• Server-system variables related to AUTO_INCREMENT (auto_increment_increment andauto_increment_offset) that can be used for replication: Section 5.1.4, “Server System Variables”.