14.8.1 Creating InnoDB Tables

To create an InnoDB table, specify an ENGINE=InnoDB option in the CREATE TABLE statement:

CREATE TABLE t1 (a INT, b CHAR (20), PRIMARY KEY (a)) ENGINE=InnoDB;

An InnoDB table and its indexes can be created in the system tablespace or in a file-per-table tablespace. When innodb_file_per_table is enabled, an InnoDB table is implicitly created in an individual file-per-table tablespace. Conversely, when innodb_file_per_table is disabled, an InnoDB table is implicitly created in the system tablespace.

When you create an InnoDB table, MySQL creates a .frm file in a database directory under the MySQL data directory. For a table created in a file-per-table tablespace, an .ibd file is also created. A table created in the system tablespace is created in the existing system tablespace ibdata files.

Internally, InnoDB adds an entry for each table to the InnoDB data dictionary. The entry includes the database name. For example, if table t1 is created in the test database, the data dictionary entry is 'test/t1'. This means you can create a table of the same name (t1) in a different database, and the table names do not collide inside InnoDB.

Viewing the Properties of InnoDB Tables

To view the properties of InnoDB tables, issue a SHOW TABLE STATUS statement:

mysql> SHOW TABLE STATUS FROM test LIKE 't%' \G;
*************************** 1. row ***************************
           Name: t1
         Engine: InnoDB
        Version: 10
     Row_format: Compact
           Rows: 0
 Avg_row_length: 0
    Data_length: 16384
Max_data_length: 0
   Index_length: 0
      Data_free: 41943040
 Auto_increment: NULL
    Create_time: 2015-03-16 16:42:17
    Update_time: NULL
     Check_time: NULL
      Collation: latin1_swedish_ci
       Checksum: NULL
 Create_options: 
        Comment: 
1 row in set (0.00 sec)

In the status output, you see the Row format property of table t1 is Compact. Although that setting is fine for basic experimentation, consider using the Dynamic or Compressed row format to take advantage of InnoDB features such as table compression and off-page storage for long column values. Using these row formats requires that innodb_file_per_table is enabled and that innodb_file_format is set to Barracuda:

SET GLOBAL innodb_file_per_table=1;
SET GLOBAL innodb_file_format=barracuda;
CREATE TABLE t3 (a INT, b CHAR (20), PRIMARY KEY (a)) ROW_FORMAT=DYNAMIC;
CREATE TABLE t4 (a INT, b CHAR (20), PRIMARY KEY (a)) ROW_FORMAT=COMPRESSED;

Defining a Primary Key for InnoDB Tables

Always set up a primary key for each InnoDB table, specifying the column or columns that:

For example, in a table containing information about people, you would not create a primary key on (firstname, lastname) because more than one person can have the same name, some people have blank last names, and sometimes people change their names. With so many constraints, often there is not an obvious set of columns to use as a primary key, so you create a new column with a numeric ID to serve as all or part of the primary key. You can declare an auto-increment column so that ascending values are filled in automatically as rows are inserted:

-- The value of ID can act like a pointer between related items in different tables.
CREATE TABLE t5 (id INT AUTO_INCREMENT, b CHAR (20), PRIMARY KEY (id));
-- The primary key can consist of more than one column. Any autoinc column must come first.
CREATE TABLE t6 (id INT AUTO_INCREMENT, a INT, b CHAR (20), PRIMARY KEY (id,a));

Although the table works correctly without defining a primary key, the primary key is involved with many aspects of performance and is a crucial design aspect for any large or frequently used table. It is recommended that you always specify a primary key in the CREATE TABLE statement. If you create the table, load data, and then run ALTER TABLE to add a primary key later, that operation is much slower than defining the primary key when creating the table.