SQL/MP Reference Manual

HP NonStop SQL/MP Reference Manual—523352-013
C-45
Columns
Columns
A column is a vertical component of a table, the relational representation of a field in a
record. A column contains one data value for each row of the table.
Each SQL column has a name that is an SQL identifier that is unique within the table
or view that contains the column.
A qualified column name is a column name qualified by the name of the table or view
to which the column belongs, or by a correlation name. If a query refers to columns
that have the same name but belong to different tables or views, you must use a
qualified column name to refer to the columns within the query. The syntax of a
qualified column name is:
If you define a correlation name for a column in the FROM clause of a statement, you
must use that correlation name (called the “explicit correlation name”) if you need to
qualify the column name within the statement.
If you do not define an explicit correlation name in the FROM clause, you can qualify
the column name with the name of the table or view that contains the column (called
the “implicit correlation name”). You can also use the name of a DEFINE that contains
the name of the table or view that contains the column as a qualifier, but you must omit
the equals sign (=) that normally precedes the DEFINE name.
You must also refer to a column by a qualified column name if you join a table with
itself within a query to compare one row of the table with other rows in the same table.
{ table-name }
{ view-name }.column-name
{ correlation-name }