InnoDB tables are created using the
CREATE TABLE statement; for
CREATE TABLE t1 (a INT, b CHAR (20), PRIMARY KEY (a)) ENGINE=InnoDB;
ENGINE=InnoDB clause is not required when
InnoDB is defined as the default storage
engine, which it is by default. However, the
ENGINE clause is useful if the
CREATE TABLE statement is to be
replayed on a different MySQL Server instance where the default
storage engine is not
InnoDB or is unknown. You
can determine the default storage engine on a MySQL Server
instance by issuing the following statement:
mysql> SELECT @@default_storage_engine; +--------------------------+ | @@default_storage_engine | +--------------------------+ | InnoDB | +--------------------------+
InnoDB tables are created in file-per-table
tablespaces by default. To create an
table in the
InnoDB system tablespace, disable
variable before creating the table. For more information, see
Section 14.6.3, “Tablespaces”.
MySQL stores data dictionary information for tables in
.frm files in database
directories. Unlike other MySQL storage engines,
InnoDB also encodes information about the
table in its own internal data dictionary inside the system
tablespace. When MySQL drops a table or a database, it deletes
one or more
.frm files as well as the
corresponding entries inside the
dictionary. You cannot move
between databases simply by moving the
files. For information about moving
tables, see Section 126.96.36.199, “Moving or Copying InnoDB Tables”.
The row format of an
InnoDB table determines
how its rows are physically stored on disk.
InnoDB supports four row formats, each with
different storage characteristics. Supported row formats include
COMPACT row format is the default. For
information about row format characteristics, see
Section 14.11, “InnoDB Row Formats”.
COMPACT row format is fine for
basic experimentation, consider using the
format to take advantage of
such as table compression and efficient off-page storage of long
The row format of a table is defined using the
ROW_FORMAT table option in a
ALTER TABLE statement. See
Defining the Row Format of a Table
It is recommended that you define a primary key for each table that you create. When selecting primary key columns, choose columns with the following characteristics:
Columns that are referenced by the most important queries.
Columns that are never left blank.
Columns that never have duplicate values.
Columns that rarely if ever change value once inserted.
For example, in a table containing information about people, you
would not create a primary key on
lastname) because more than one person can have the
same name, a name column may be left blank, 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
so that ascending values are filled in automatically as rows are
# 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));
For more information about auto-increment columns, see Section 188.8.131.52, “AUTO_INCREMENT Handling in InnoDB”.
Although a 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
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. For more information about primary
keys, see Section 184.108.40.206, “Clustered and Secondary Indexes”.
To view the properties of an
SHOW TABLE STATUS
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 16:26:52 Update_time: NULL Check_time: NULL Collation: latin1_swedish_ci Checksum: NULL Create_options: Comment: 1 row in set (0.00 sec)
You can also access
InnoDB table properties
by querying the
InnoDB Information Schema
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_SYS_TABLES WHERE NAME='test/t1' \G *************************** 1. row *************************** TABLE_ID: 42 NAME: test/t1 FLAG: 1 N_COLS: 5 SPACE: 24 FILE_FORMAT: Antelope ROW_FORMAT: Compact ZIP_PAGE_SIZE: 0 1 row in set (0.02 sec)
For more information, see Section 14.15.3, “InnoDB INFORMATION_SCHEMA System Tables”.