Identifier Qualifiers - Oracle 5.0 Reference Manual

The following table describes the maximum length for each type of identifier.
Identifier
Database
Table
Column
Index
Constraint
Stored Procedure or Function
Trigger
View
Alias
Compound Statement Label
As of MySQL 5.0.52, aliases for column names in
maximum column length of 64 characters (not the maximum alias length of 256 characters).
Identifiers are stored using Unicode (UTF-8). This applies to identifiers in table definitions that are
stored in
.frm
the identifier string columns in the grant tables are measured in characters. You can use multi-byte
characters without reducing the number of characters permitted for values stored in these columns,
something not true prior to MySQL 4.1. As indicated earlier, the permissible Unicode characters are
those in the Basic Multilingual Plane (BMP). Supplementary characters are not permitted.

9.2.1. Identifier Qualifiers

MySQL permits names that consist of a single identifier or multiple identifiers. The components of a
multiple-part name must be separated by period (".") characters. The initial parts of a multiple-part
name act as qualifiers that affect the context within which the final identifier is interpreted.
In MySQL, you can refer to a table column using any of the following forms.
Column Reference
col_name
tbl_name.col_name
db_name.tbl_name.col_name
The qualifier character is a separate token and need not be contiguous with the associated identifiers.
For example,
If any components of a multiple-part name require quoting, quote them individually rather than quoting
the name as a whole. For example, write `my-table`.`my-column`, not
column`.
A reserved word that follows a period in a qualified name must be an identifier, so in that context it
need not be quoted.
You need not specify a
statement unless the reference would be ambiguous. Suppose that tables
a column c, and you retrieve
ambiguous because it is not unique among the tables used in the statement. You must qualify it with a
table name as
files and to identifiers stored in the grant tables in the
Meaning
The column
contains a column of that name.
The column
The column
db_name.
tbl_name.col_name
or
tbl_name
in a
c SELECT
or to indicate which table you mean. Similarly, to retrieve from a table
t1.c t2.c
Identifier Qualifiers
Maximum Length (characters)
64
64
64
64
64
64
64
64
256 (see exception following table)
16
CREATE VIEW
from whichever table used in the statement
col_name
from table
col_name
from table
col_name
and
tbl_name . col_name
db_name.tbl_name
statement that uses both
753
statements are checked against the
database. The sizes of
mysql
of the default database.
tbl_name
of the database
tbl_name
are equivalent.
`my-table.my-
prefix for a column reference in a
and
t1 t2
and t2. In this case,
t1
each contain
is
c
in
t