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Qualifiers have these characteristics: 

•An unqualified name consists of a single identifier. A qualified name consists of 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 to interpret the final identifier. 

•The qualifier character is a separate token and need not be contiguous with the associated identifiers. For example, tbl_name.col_name  and tbl_name . 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 ‘my-table‘.‘my-column‘ , not ‘my-table.my-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. 

The permitted qualifiers for object names depend on the object type: 

•A database name is fully qualified and takes no qualifier: 

CREATE DATABASE db1; 

•A table, view, or stored program name may be given a database-name qualifier. Examples of unqualified and qualified names in CREATE  statements: 

CREATE TABLE mytable ...; CREATE VIEW myview ...; CREATE PROCEDURE myproc ...; CREATE FUNCTION myfunc ...; CREATE EVENT myevent ...; CREATE TABLE mydb.mytable ...; CREATE VIEW mydb.myview ...; CREATE PROCEDURE mydb.myproc ...; CREATE FUNCTION mydb.myfunc ...; CREATE EVENT mydb.myevent ...; 

•A trigger is associated with a table, so any qualifier applies to the table name: 

CREATE TRIGGER mytrigger ... ON mytable ...; CREATE TRIGGER mytrigger ... ON mydb.mytable ...; 

•A column name may be given multiple qualifiers to indicate context in statements that reference it, as shown in the following table. 

<img src='content_image/800419.jpg'>

In other words, a column name may be given a table-name qualifier, which itself may be given a database-name qualifier. Examples of unqualified and qualified column references in SELECT statements: 

SELECT c1 FROM mytable 

