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.
The qualifier character is a separate token and need not be contiguous with the associated identifiers. For
. col_name are equivalent.
If any components of a multiple-part name require quoting, quote them individually rather than quoting the name
as a whole. For example, write
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
prefix for a column reference in a statement unless the reference would be ambiguous. Suppose that tables
t2 each contain a column
c, and you retrieve
c in a
SELECT statement that uses both
t2. In this case,
c is ambiguous because it is not
unique among the tables used in the statement. You must qualify it with a table name as
t2.c to indicate which table you mean. Similarly, to retrieve from a table
t in database
db1 and from a table
t in database
db2 in the same statement, you must
refer to columns in those tables as
means the table
tbl_name in the default database. This syntax is accepted for ODBC
compatibility because some ODBC programs prefix table names with a "