4.13 When Directive

The WHEN directive is used when you want to include multiple record definitions or REDEFINES in a database table. It's typically used when you want to force certain columns to be built that wouldn't be built by default (because you want to use them from the RDBMS side).

Recall that the key fields and the fields from the largest record are automatically included as explicit columns in the database table. All fields are stored and retrieved from the database, whether they appear as explicit columns or not. So you don't need to use WHEN unless you want to ensure that some additional fields are explicitly listed by name in the table.

WHEN declares that the field (or subordinate fields, if it is a group item) that immediately follow the directive must appear as a column (or columns) in the database table. It also states one condition under which the columns are to be used. The WHEN directive guarantees that the fields will be explicitly included in the table - as long as they aren't FILLER and don't occupy the same area as key fields.

The WHEN directive results in a table that unites all fields subordinate to the WHEN directive. This table might include more columns, and could impact performance and storage requirements.

Syntax

$XFD WHEN field=value      (equals)
$XFD WHEN field<=value     (is less than or equals)
$XFD WHEN field<value      (is less than)
$XFD WHEN field>=value     (is greater than or equals)
$XFD WHEN field>value      (is greater than)
$XFD WHEN field!=value     (is not equal to)
$XFD WHEN field=OTHER
          or
*(( XFD WHEN field=value ))  (also <, <=, >, >=, !=)

The value may be an explicit data value (in quotes). The word OTHER can be used only with =. It means use the following field(s) only if the WHEN condition(s) listed at the level of this field are not met.

Note: WHEN values must be on individual lines as single values in the code. WHEN values cannot be combined.

For example:

   03  ar-code-type                  pic x.
   *(( xfd  when ar-code-type = "s" ))
   03  ship-code-record              pic x(4).
   *(( xfd  when ar-code-type = "b" ))
   03  backorder-code-record redefines ship-code-record.
   *(( xfd  when ar-code-type = other ))
   03  obsolete-code-record redefines ship-code-record.

OTHER may be used before one record definition, and may be used once at each level within each record definition.

Note: A WHEN directive with condition OTHER must be used if there is a possibility that the data in the field will not meet any of the explicit conditions specified in the other WHEN directives. If this is not done, results are undefined.

Example 1

If the following code were compiled without directives, the underlined fields would appear explicitly in the database table. Note that the key fields would be included automatically, as would the fields from the largest record. FILLER would be ignored:

01      ar-codes-record.
   03      ar-codes-key.
      05      ar-code-type                   pic x.
      05      ar-code-num                    pic 999.
01      ship-code-record.
   03      filler                            pic x(4).
   03      ship-instruct                     pic x(15).
01      terms-code-record.
   03      filler                            pic x(4).
   03      terms-rate-1                      pic s9v999.
   03      terms-days-1                      pic 9(3).
   03      terms-rate-2                      pic s9v999.
   03      terms-descript                    pic x(15).

If you added the WHEN directive as shown below, it would cause the fields from the SHIP-CODE-RECORD to be included in the database table, and would determine when specific database columns would be used. The underlined fields would appear as columns in the database table:

01      ar-codes-record.
   03      ar-codes-key.
      05      ar-code-type                   pic x.
      05      ar-code-num                    pic 999.
$xfd  when ar-code-type = "s"
01      ship-code-record.
   03      filler                            pic x(4).
   03      ship-instruct                     pic x(15).
$xfd  when ar-code-type = "t"
01      terms-code-record.
   03      filler                            pic x(4).
   03      terms-rate-1                      pic s9v999.
   03      terms-days-1                      pic 9(3).
   03      terms-rate-2                      pic s9v999.
   03      terms-descript                    pic x(15).

FILLER data items don't have unique names and are thus not used to form columns in the database table. You could use the NAME directive to give them a name if you really need to see them in the database table.

Note: In this example, the FILLER data items implicitly redefine key fields. Thus, they would be disregarded even if you provided a name for them.

Example 2

In the following code, in which no WHEN directives are used, the underlined fields will be explicitly named in the database table. (Key fields have the suffix key in their names in this example.)

Note that REDEFINES records simply re-map the same data area and are not explicitly included in the database table by default:

01      archive-record.
   03      filler                        pic x(33).
   03      archive-code                  pic 9(6).
   03      archive-location              pic 9(2).
   03      filler                        pic x(10).
01      master-record.
   03      animal-id-key.
      05      patient-id                 pic 9(6).
      05      species-code-type          pic 9(5).
      05      species-name               pic x(6).
   03      service-code-key.
      05      service-code-type          pic 9(6).
      05      service-name               pic x(10).
   03      billing-code.
      05      billing-code-type          pic 9(4).
      05      plan-name                  pic x(8).
   03      office-info.
      05      date-in-office             pic 9(8).
      05      served-by-name             pic x(10).
   03      remote-info redefines office-info.
      05      van-id                     pic 9(4).
      05      proc-code                  pic 9(8).
      05      vet-name                   pic x(6).

If you added the WHEN directives shown below, you would add several columns to the database table. The fields that would appear in the table are underlined:

*(( xfd when animal-id-key = "00000000000000000" ))
01      archive-record.
   03      filler                        pic x(33).
   03      archive-code                  pic 9(6).
   03      archive-location              pic 9(2).
   03      filler                        pic x(10).
*(( xfd  when animal-id-key =  other ))
01  master-record.
*(( xfd  use group ))
   03      animal-id-key.
      05      patient-id                  pic 9(6).
      05      species-code-type           pic 9(5).
      05      species-name                pic x(6).
   03      service-code-key.
      05      service-code-type           pic 9(6).
      05      service-name                pic x(10).
   03      billing-code.
      05      billing-code-type           pic 9(4).
      05      plan-name                   pic x(8).
*(( xfd when billing-code-type = "1440" ))
   03      office-info.
      05      date-in-office              pic 9(8).
      05      served-by-name              pic x(10).
*(( xfd when billing-code-type = other ))
   03      remote-info redefines office-info.
      05      van-id                      pic 9(4).
      05      proc-code                   pic 9(8).
      05      vet-name                    pic x(6).

Example 3

If your application has a REDEFINES whose field names are more meaningful than the fields they redefine, you might consider switching the order of your code, rather than using a WHEN directive. Use the less significant field names in the REDEFINES.

For example, you might change this:

   03      code-info.
      05      filler                  pic 9(8).
      05      code-1                  pic x(10).
   03      patient-info redefines code-info.
      05      patient-id              pic 9(4).
      05      service-code             pic 9(8).
      05      server-name             pic x(6).

to this:

   03      patient-info.
      05      patient-id              pic 9(4).
      05      service-code            pic 9(8).
      05      server-name             pic x(6).
   03      code-info redefines patient-info.
      05      filler                  pic 9(8).
      05      code-1                  pic x(10).

The fields that would appear in the database table by default are underlined above. This shows how the column names might become more meaningful when the order is reversed. Your application operates the same either way.

Note: When a WHEN directive condition is met, COBOL record definitions or REDEFINES records that are subordinate to other WHEN directives are not used. Database columns in rows that correspond to those records are set to the special database value NULL. This means that there is no value provided for those columns. NULL is not equivalent to zero, and it has special properties in the RDBMS. For example, you can select all rows for which a given column is NULL.

Example 4

This COBOL code:

01      col-type                        pic x.
$   xfd  when col-type = "a"
   03      def1                         pic x(2).
   $xfd  when col-type = "b"
   03      def2 redefines def1          pic 9(2).

will result in this database table:

col_type
def1
def2
a
Xx
<Null>
b
<Null>
10