The KEY statement specifies a BY key for an elementary
data field. This field must be an ADABAS descriptor.
A BY key, which is an
optional set of match variables, is used only when the interface view
engine must examine additional ADABAS records in order to add a new
periodic group occurrence. The engine uses the BY key variables in
temporary WHERE clauses that are designed to locate a record for modification.
Examining the additional ADABAS records is required only if data
is changed above the periodic group level from one observation to
the next in a view descriptor with a selected periodic group. It
is suggested that you use BY key variables even if they are not always
needed.
A data field is a good
candidate for a BY key variable if it uniquely identifies a logical
record. The incoming values of the data fields in a BY key variable
are matched to existing values in order to locate a position in which
to insert new periodic groups. (A BY key variable is similar to a
BY group or a BY variable in SAS.)
The KEY statement can
have the following values:
(default) indicates
that the data field is not to be used as a KEY.
specifies that the
data field is not to be used as a KEY.
specifies that the
data field is to be used as a KEY.
An editing statement,
such as KEY, must follow the CREATE statement and the database-description
statements when you create a descriptor.
See CREATE Statement for more information
about the order of statements.
You can use the KEY
statement with a view descriptor only if the ASSIGN statement that
was used when creating the access descriptor was specified with the
NO value.
You do not have to issue
a SELECT statement in a view descriptor for the columns included in
the KEY statement. The KEY statement selects the columns. When you
use the KEY statement with an access descriptor, the KEY statement
reselects columns that were previously dropped with the DROP statement.