MySQL 5.7 Release Notes
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 21.2.7.5, “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.