Syntax Elements - Teradata Database

Select List

*

All columns of all tables referenced in the FROM clause be returned.

When qualified by table_name, specifies that all columns of table_name only are to be returned.

View columns are explicitly enumerated when views are defined. If a table is changed after a view is defined, those changes will not appear if you perform a SELECT * query.

SELECT * …  is a column operation, projecting all the columns of a table. SELECT COUNT(*)… is a row operation, restricting and counting all the rows of a table, then reporting the cardinality of the table in question. The function of the asterisk differs in the two cases.

Since these derived columns are not actual columns of a table, you must explicitly specify PARTITION or PARTITION#L n, where n ranges from 1 to 62, inclusive, to project the PARTITION or PARTITION#L n columns for the table.

expression

SQL expression, including scalar subqueries and scalar UDFs.

If you specify a scalar UDF, it must return a value expression.

You can specify an expression that returns a UDT in a column list only if its transform group has a fromsql routine. The system automatically converts the expression from its UDT value to the external type via the fromsql routine before returning it to a client application. See Specifying UDTs in an SQL Request.

AS

Optional introduction to derived_column_name.

expression_alias_name

An alias for the column expression that is derived from expression. You must specify a derived_column_name for self-join operations.

table_name

Name of a table, queue table, derived table, or view.

table_name.* in the select list can define the table from which rows are to be returned when two or more tables are referenced in the FROM clause.