15.8.1 Creating InnoDB Tables

To create an InnoDB table, use the CREATE TABLE statement. You do not need to specify the ENGINE=InnoDB clause if InnoDB is defined as the default storage engine, which is the default as of MySQL 5.5. You might still use ENGINE=InnoDB clause if you plan to use mysqldump or replication to replay the CREATE TABLE statement on a server where the default storage engine is not InnoDB.

-- Default storage engine = InnoDB.
CREATE TABLE t1 (a INT, b CHAR (20), PRIMARY KEY (a));
-- Backward-compatible with older MySQL.
CREATE TABLE t2 (a INT, b CHAR (20), PRIMARY KEY (a)) ENGINE=InnoDB;

An InnoDB table and its indexes can be created in the system tablespace, in a file-per-table tablespace, or in a general tablespace (introduced in MySQL 5.7.6). When innodb_file_per_table is enabled, which is the default setting as of MySQL 5.6.6, 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. With the introduction of general tablespaces in MySQL 5.7.6, you can use CREATE TABLE ... TABLESPACE syntax to explicitly create an InnoDB table in any of the three tablespace types.

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. A table created in a general tablespace is created in an existing general tablespace .ibd file.

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: 0
 Auto_increment: NULL
    Create_time: 2015-03-16 15:13:31
    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. The Dynamic or Compressed row format is required take advantage of InnoDB features such as table compression and off-page storage for long column values. To use these row formats, you can enable innodb_file_per_table (the default as of MySQL 5.6.6) and set innodb_file_format to Barracuda, which implicitly creates InnoDB tables in file-per-table tablespaces:

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;

Or, you can use CREATE TABLE ... TABLESPACE syntax to create an InnoDB table in a general tablespace. General tablespaces support all row formats. For more information, see Section 15.7.9, “InnoDB General Tablespaces”.

CREATE TABLE t1 (c1 INT PRIMARY KEY) TABLESPACE ts1 ROW_FORMAT=DYNAMIC;

CREATE TABLE ... TABLESPACE syntax can also be used to create InnoDB tables with a Dynamic row format in the system tablespace, along side tables with a Compact or Redundant row format.

CREATE TABLE t1 (c1 INT PRIMARY KEY) TABLESPACE = innodb_system ROW_FORMAT=DYNAMIC;

InnoDB table properties may also be queried using the InnoDB Information Schema system tables:

SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME='test/t1' \G
*************************** 1. row ***************************
     TABLE_ID: 45
         NAME: test/t1
         FLAG: 1
       N_COLS: 5
        SPACE: 35
  FILE_FORMAT: Antelope
   ROW_FORMAT: Compact
ZIP_PAGE_SIZE: 0
   SPACE_TYPE: Single
1 row in set (0.00 sec)

Defining a Primary Key for InnoDB Tables

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

• Are referenced by the most important queries.

• Are never left blank.

• Never have duplicate values.

• Rarely if ever change value once inserted.

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.