MySQL 9.4 Release Notes
MySQL 9.4 supports generated invisible primary keys
for any InnoDB table that is
created without an explicit primary key. When the
sql_generate_invisible_primary_key
server system variable is set to ON, the
MySQL server automatically adds a generated invisible primary
key (GIPK) to any such table. This setting has no effect on
tables created using any other storage engine than
InnoDB.
By default, the value of
sql_generate_invisible_primary_key is
OFF, meaning that the automatic addition of
GIPKs is disabled. To illustrate how this affects table
creation, we begin by creating two identical tables, neither
having a primary key, the only difference being that the first
(table auto_0) is created with
sql_generate_invisible_primary_key set to
OFF, and the second
(auto_1) after setting it to
ON, as shown here:
mysql> SELECT @@sql_generate_invisible_primary_key;
+--------------------------------------+
| @@sql_generate_invisible_primary_key |
+--------------------------------------+
| 0 |
+--------------------------------------+
1 row in set (0.00 sec)
mysql> CREATE TABLE auto_0 (c1 VARCHAR(50), c2 INT);
Query OK, 0 rows affected (0.02 sec)
mysql> SET sql_generate_invisible_primary_key=ON;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT @@sql_generate_invisible_primary_key;
+--------------------------------------+
| @@sql_generate_invisible_primary_key |
+--------------------------------------+
| 1 |
+--------------------------------------+
1 row in set (0.00 sec)
mysql> CREATE TABLE auto_1 (c1 VARCHAR(50), c2 INT);
Query OK, 0 rows affected (0.04 sec)
Compare the output of these SHOW CREATE
TABLE statements to see the difference in how the
tables were actually created:
mysql> SHOW CREATE TABLE auto_0\G
*************************** 1. row ***************************
Table: auto_0
Create Table: CREATE TABLE `auto_0` (
`c1` varchar(50) DEFAULT NULL,
`c2` int DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
mysql> SHOW CREATE TABLE auto_1\G
*************************** 1. row ***************************
Table: auto_1
Create Table: CREATE TABLE `auto_1` (
`my_row_id` bigint unsigned NOT NULL AUTO_INCREMENT /*!80023 INVISIBLE */,
`c1` varchar(50) DEFAULT NULL,
`c2` int DEFAULT NULL,
PRIMARY KEY (`my_row_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
Since auto_1 had no primary key specified by
the CREATE TABLE statement used to create it,
setting sql_generate_invisible_primary_key =
ON causes MySQL to add both the invisible column
my_row_id to this table and a primary key on
that column. Since
sql_generate_invisible_primary_key was
OFF at the time that
auto_0 was created, no such additions were
performed on that table.
When a primary key is added to a table by the server, the column
and key name is always my_row_id. For this
reason, when enabling generated invisible primary keys in this
way, you cannot create a table having a column named
my_row_id unless the table creation statement
also specifies an explicit primary key. (You are not required to
name the column or key my_row_id in such
cases.)
my_row_id is an invisible column, which means
it is not shown in the output of
SELECT * or
TABLE; the column must be
selected explicitly by name. See
Section 15.1.24.10, “Invisible Columns”.
When GIPKs are enabled, a generated primary key cannot be
altered other than to switch it between
VISIBLE and INVISIBLE. To
make the generated invisible primary key on
auto_1 visible, execute this
ALTER TABLE statement:
mysql> ALTER TABLE auto_1 ALTER COLUMN my_row_id SET VISIBLE;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> SHOW CREATE TABLE auto_1\G
*************************** 1. row ***************************
Table: auto_1
Create Table: CREATE TABLE `auto_1` (
`my_row_id` bigint unsigned NOT NULL AUTO_INCREMENT,
`c1` varchar(50) DEFAULT NULL,
`c2` int DEFAULT NULL,
PRIMARY KEY (`my_row_id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.01 sec)
To make this generated primary key invisible again, issue
ALTER TABLE auto_1 ALTER COLUMN my_row_id SET
INVISIBLE.
A generated invisible primary key is always invisible by default.
Whenever GIPKs are enabled, you cannot drop a generated primary key if either of the following 2 conditions would result:
The table is left with no primary key.
The primary key is dropped, but not the primary key column.
The effects of
sql_generate_invisible_primary_key apply to
tables using the InnoDB storage engine only.
You can use an ALTER TABLE
statement to change the storage engine used by a table that has
a generated invisible primary key; in this case, the primary key
and column remain in place, but the table and key no longer
receive any special treatment.
By default, GIPKs are shown in the output of
SHOW CREATE TABLE,
SHOW COLUMNS, and
SHOW INDEX, and are visible in
the Information Schema COLUMNS and
STATISTICS tables. You can cause
generated invisible primary keys to be hidden instead in such
cases by setting the
show_gipk_in_create_table_and_information_schema
system variable to OFF. By default, this
variable is ON, as shown here:
mysql> SELECT @@show_gipk_in_create_table_and_information_schema;
+----------------------------------------------------+
| @@show_gipk_in_create_table_and_information_schema |
+----------------------------------------------------+
| 1 |
+----------------------------------------------------+
1 row in set (0.00 sec)
As can be seen from the following query against the
COLUMNS table, my_row_id
is visible among the columns of auto_1:
mysql> SELECT COLUMN_NAME, ORDINAL_POSITION, DATA_TYPE, COLUMN_KEY
-> FROM INFORMATION_SCHEMA.COLUMNS
-> WHERE TABLE_NAME = "auto_1";
+-------------+------------------+-----------+------------+
| COLUMN_NAME | ORDINAL_POSITION | DATA_TYPE | COLUMN_KEY |
+-------------+------------------+-----------+------------+
| my_row_id | 1 | bigint | PRI |
| c1 | 2 | varchar | |
| c2 | 3 | int | |
+-------------+------------------+-----------+------------+
3 rows in set (0.01 sec)
After
show_gipk_in_create_table_and_information_schema
is set to OFF, my_row_id
can no longer be seen in the COLUMNS table,
as shown here:
mysql> SET show_gipk_in_create_table_and_information_schema = OFF;
Query OK, 0 rows affected (0.00 sec)
mysql> SELECT @@show_gipk_in_create_table_and_information_schema;
+----------------------------------------------------+
| @@show_gipk_in_create_table_and_information_schema |
+----------------------------------------------------+
| 0 |
+----------------------------------------------------+
1 row in set (0.00 sec)
mysql> SELECT COLUMN_NAME, ORDINAL_POSITION, DATA_TYPE, COLUMN_KEY
-> FROM INFORMATION_SCHEMA.COLUMNS
-> WHERE TABLE_NAME = "auto_1";
+-------------+------------------+-----------+------------+
| COLUMN_NAME | ORDINAL_POSITION | DATA_TYPE | COLUMN_KEY |
+-------------+------------------+-----------+------------+
| c1 | 2 | varchar | |
| c2 | 3 | int | |
+-------------+------------------+-----------+------------+
2 rows in set (0.00 sec)
The setting for
sql_generate_invisible_primary_key is not
replicated, and is ignored by replication applier threads. This
means that the setting of this variable on the source has no
effect on the replica. You can cause the replica to add a GIPK
for tables replicated without primary keys on a given
replication channel using
REQUIRE_TABLE_PRIMARY_KEY_CHECK = GENERATE as
part of a
CHANGE
REPLICATION SOURCE TO statement.
GIPKs work with row-based replication of
CREATE
TABLE ... SELECT; the information written to the
binary log for this statement in such cases includes the GIPK
definition, and thus is replicated correctly. Statement-based
replication of CREATE TABLE ... SELECT is not
supported with sql_generate_invisible_primary_key =
ON.
When creating or importing backups of installations where GIPKs
are in use, it is possible to exclude generated invisible
primary key columns and values. The
--skip-generated-invisible-primary-key
option for mysqldump causes GIPK information
to be excluded in the program's output.