A sequence is a set of integers 1, 2, 3. that are generated in order on demand. Sequences are frequently used in databases because many applications require each row in a table to contain a unique value and sequences provide an easy way to generate them. This chapter describes how to use sequences in My SQL. Using AUTO_ INCREMENT column: The simplest way in My SQL to use Sequences is to define a column as AUTO_ INCREMENT and leave rest of the things to My SQL to take care. Example: Try out the following example. This will create table and after that it will insert few rows in this table where it is not required to give record ID because it's auto incremented by My SQL. 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 kitchen -> ( NULL millipede driveway -> ( NULL grasshopper 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 | | kitchen | | 2 | millipede | | driveway | | 3 | grasshopper | | front yard | +-+ + + + 3 rows in set (0.00 sec) Obtain AUTO_ INCREMENT Values: LAST_ INSERT_ ID( ) is a SQL function, so you can use it from within any client that understands how to issue SQL statements. Otherwise, PERL and PHP scripts provide exclusive functions to retrieve auto incremented value of last record. PERL Example: Use the mysql_insertid attribute to obtain.
A common practice in database design is to set primary keys ( PKs) with auto increment enabled. This way, you don't have to worry about specifying a new unique primary key value each time you insert a new record in such table. While php My Admin is a very powerful and easy to use My SQL database management tool, where could I set auto increment in php My Admin is still a frequent question. And here is the solution. In the latest php My Admin versions there is a new A_ I Checkbox. Mark this option as enabled when creating or editing your primary key table column and that numeric field will automatically increment its value each time a new record is inserted. You can check that the auto increment property was successfully setup in the EXTRA column of the table column properties (after selecting a table, inside the structure tab). If the auto_increment text appears here, the configuration was successful. In previous php My Admin versions, auto_increment was an additional option inside the dropdown menu of the EXTRA category (the last column in the field creation menu). To access the edit table field menu you can click the pencil icon in the desired table field row, inside the Structure tab. Anyway, you can always run an SQL command to update the auto increment status of the desired column by selecting the SQL tab and writing an SQL query like this one: ALTER TABLE ` CHANGE ` ` INT NOT NULL AUTO_ INCREMENT Just replace table_name by the name of the current table being edited, pk_column_name by the column name of your primary key column and key_length by your integer primary key length (the default int length is 11). You should also make sure that the auto incrementing field is in fact the primary key of the current table. You can reset the table primary key by clicking on the table key icon of the desired field row. Take also into account that only one auto.
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 My SQL 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. When you insert any other value into an AUTO_ INCREMENT column, the column is set to that value and the sequence is reset so that the next automatically generated value follows sequentially from the largest column value. You can retrieve the most recent automatically generated AUTO_ INCREMENT value with the LAST_ INSERT_ ID SQL function or the mysql_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, “ Integer Types ( Exact Value) - INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT” for the ranges of all the integer types. Note For a multiple-row insert.
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