Referencing Object Names in a Request
When you reference an object name in a request, you may need to qualify the name. The topics that follow explain the rules for use of qualified and unqualified object names.
The following example shows unqualified, qualified and a fully qualified name references in a SELECT statement that accesses the Employee table in the personnel database:
SELECT Name, DeptNo, JobTitle
FROM Personnel.Employee
WHERE Personnel.Employee.DeptNo = 100 ;
Fully Qualified Object Names
A fully qualified object name includes the names of all parent objects up to the level of the containing database. A common use case is a fully qualified column name, which consists of a database name, table name, and column name.
where:
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This Syntax element … |
Specifies … |
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database_name |
a qualifying name for the database in which the table and column being referenced is stored. Depending on the ambiguity of the reference, database_name might or might not be required. |
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table_name |
a qualifying name for the table in which the column being referenced is stored. Depending on the ambiguity of the reference, table_name might or might not be required. |
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column_name |
one of the following: |
Name Resolution Rules and the Need to Fully Qualify a Name
Therefore, you should fully qualify all names in a macro data definition statement, unless you specifically intend for the user’s default to be used.
Whether unqualified object names acquire the database name of the creator, invoker, or owner of the stored procedure also depends on whether the CREATE PROCEDURE statement includes the SQL SECURITY clause and which option the clause specifies.
Unqualified Object Names
An unqualified object name is a reference to an object such as a table, column, trigger, macro, or stored procedure that does not include parent objects. For example, the WHERE clause in the following statement uses “DeptNo” as an unqualified column name:
SELECT *
FROM Personnel.Employee
WHERE DeptNo = 100 ;
Unqualified Column Names
You can omit database and table name qualifiers when you reference columns as long as the reference is not ambiguous.
For example, the WHERE clause in the following statement:
SELECT Name, DeptNo, JobTitle
FROM Personnel.Employee
WHERE Personnel.Employee.DeptNo = 100 ;
can be written as:
WHERE DeptNo = 100 ;
because the database name and table name can be derived from the Personnel.Employee reference in the FROM clause.
Omitting Database Names
When you omit the database name qualifier, Teradata Database looks in the following databases to find the unqualified object name:
The search must find the name in only one of those databases. An ambiguous name error message results if the name exists in more than one of those databases.
For example, if your login user database has no volatile tables named Employee and you have established Personnel as your default database, you can omit the Personnel database name qualifier from the preceding sample query.
Related Topics
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For more information on, for example… |
See … |
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default databases |
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the DATABASE statement |
SQL Data Definition Language. |
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the CREATE USER statement |
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the MODIFY USER statement |
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the CREATE PROCEDURE statement and the SQL SECURITY clause |
Using a Column Alias
In addition to referring to a column by name, an SQL query can reference a column by an alias. Column aliases are used for join indexes when two columns have the same name. However, an alias can be used for any column when a pseudonym is more descriptive or easier to use. Using an alias to name an expression allows a query to reference the expression.
You can specify a column alias with or without the keyword AS on the first reference to the column in the query. The following example creates and uses aliases for the first two columns.
SELECT departnumber AS d, employeename e, salary
FROM personnel.employee
WHERE d IN(100, 500)
ORDER BY d, e ;
Alias names must meet the same requirements as names of other database objects.
The scope of alias names is confined to the query.
Referencing All Columns in a Table
An asterisk references all columns in a row simultaneously, for example, the following SELECT statement references all columns in the Employee table. A list of those fully qualified column names follows the query.
SELECT * FROM Employee;
Personnel.Employee.EmpNo
Personnel.Employee.Name
Personnel.Employee.DeptNo
Personnel.Employee.JobTitle
Personnel.Employee.Salary
Personnel.Employee.YrsExp
Personnel.Employee.DOB
Personnel.Employee.Sex
Personnel.Employee.Race
Personnel.Employee.MStat
Personnel.Employee.EdLev
Personnel.Employee.HCap