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MySQL 5.7 Reference Manual  /  ...  /  Identifier Length Limits

9.2.1 Identifier Length Limits

The following table describes the maximum length for each type of identifier.

Identifier Type Maximum Length (characters)
Database 64 (NDB storage engine: 63)
Table 64 (NDB storage engine: 63)
Column 64
Index 64
Constraint 64
Stored Program 64
View 64
Tablespace 64
Server 64
Log File Group 64
Alias 256 (see exception following table)
Compound Statement Label 16
User-Defined Variable 64

Aliases for column names in CREATE VIEW statements are checked against the maximum column length of 64 characters (not the maximum alias length of 256 characters).

For constraint definitions that include no constraint name, the server internally generates a name derived from the associated table name. For example, internally generated foreign key constraint names consist of the table name plus _ibfk_ and a number. If the table name is close to the length limit for constraint names, the additional characters required for the constraint name may cause that name to exceed the limit, resulting in an error.

Identifiers are stored using Unicode (UTF-8). This applies to identifiers in table definitions that are stored in .frm files and to identifiers stored in the grant tables in the mysql database. The sizes of the identifier string columns in the grant tables are measured in characters. You can use multibyte characters without reducing the number of characters permitted for values stored in these columns.

NDB Cluster imposes a maximum length of 63 characters for names of databases and tables. See Section, “Limits Associated with Database Objects in NDB Cluster”.

Values such as user name and host names in MySQL account names are strings rather than identifiers. For information about the maximum length of such values as stored in grant tables, see Grant Table Scope Column Properties.