If you have a null-capable key field, you can search for records containing null values by specifying an indicator in factor 2 of the KFLD operation and setting that indicator on before the keyed input operation. If you do not want a null key to be selected, you set the indicator off.
When a record format with null-capable key fields is used on a CHAIN, SETLL, READE, or READPE operation, and a %KDS data structure is used to specify the keys, then the null-key-byte-map information will be taken from the null attributes of the subfields in the data structure specified as the argument of %KDS.
When a record format with null-capable key fields is used on a CHAIN, SETLL, READE, or READPE operation, and a list of keyfields is used, then the null-key-byte-map information will be taken from the null attributes of the specified keys.
Figure 104 and Figure 105 illustrate how keyed operations are used to position and retrieve records with null keys.
// Assume File1 below contains a record Rec1 with a composite key
// made up of three key fields: Key1, Key2, and Key3. Key2 and Key3
// are null-capable. Key1 is not null-capable.
// Each key field is two characters long.
*..1....+....2....+....3....+....4....+....5....+....6....+....7....+..
FFilename++IPEASFRlen+LKlen+AIDevice+.Keywords++++++++++++++++++++++++++
FFile1 IF E DISK
// Define two data structures with the keys for the file
// Subfields Key2 and Key3 of both data structures will be
// null-capable.
DName+++++++++++ETDsFrom+++To/L+++IDc.Keywords+++++++++++++++++++++++++
D Keys DS LIKEREC(Rec1 : *KEY)
D OtherKeys DS LIKEDS(keys)
// Define a data structure with the input fields of the file
// Subfields Key2 and Key3 of the data structures will be
// null-capable.
D File1Flds DS LIKEREC(Rec1 : *INPUT)
/free
// The null indicator for Keys.Key2 is ON and the
// null indicator for Keys.Key3 is OFF, for the
// SETLL operation below. File1 will be positioned
// at the next record that has a key that is equal
// to or greater than 'AA??CC' (where ?? is used
// in this example to indicate NULL)
// Because %NULLIND(Keys.Key2) is ON, the actual content
// in the search argument Keys.Key2 will be ignored.
// If a record exists in File1 with 'AA' in Key1, a null
// Key2, and 'CC' in Key3, %EQUAL(File1) will be true.
Keys.Key1 = 'AA';
Keys.Key3 = 'CC';
%NULLIND(Keys.Key2) = *ON;
%NULLIND(Keys.Key3) = *OFF;
SETLL %KDS(Keys) Rec1;
// The CHAIN operation below will retrieve a record
// with 'JJ' in Key1, 'KK' in Key2, and a null Key3.
// Since %NULLIND(OtherKeys.Key3) is ON, the value of
// 'XX' in OtherKeys.Key3 will not be used. This means
// that if File1 actually has a record with a key
// 'JJKKXX', that record will not be retrieved.
OtherKeys.Key3 = 'XX';
%NULLIND(Keys.Key3) = *ON;
CHAIN ('JJ' : 'KK' : OtherKeys.Key3) Rec1;
// The CHAIN operation below uses a partial key as the
// search argument. It will retrieve a record with 'NN'
// in Key1, a null key2, and any value including a null
// value in Key3. The record is retrieved into the
// File1Flds data structure, which will cause the
// null flags for File1Flds.Key2 and File1Flds.Key3
// to be changed by the operation (if the CHAIN
// finds a record).
Keys.Key1 = 'NN';
%NULLIND(Keys.Key2) = *ON;
CHAIN %KDS(Keys : 2) Rec1 File1Flds;
* Using the same file as the previous example, define two
* key lists, one containing three keys and one containing
* two keys.
CL0N01Factor1+++++++Opcode(E)+Factor2+++++++Result++++++++Len++D+HiLoEq.
C Full_Kl KLIST
C KFLD Key1
C KFLD *IN02 Key2
C KFLD *IN03 Key3
C Partial_Kl KLIST
C KFLD Key1
C KFLD *IN05 Key2
*
* *IN02 is ON and *IN03 is OFF for the SETLL operation below.
* File1 will be positioned at the next record that has a key
* that is equal to or greater than 'AA??CC' (where ?? is used
* in this example to indicate NULL)
*
* Because *IN02 is ON, the actual content in the search argument
* for Key2 will be ignored.
*
* If a record exists in File1 with 'AA' in Key1, a null Key2, and
* 'CC' in Key3, indicator 90 (the Eq indicator) will be set ON.
*
C MOVE 'AA' Key1
C MOVE 'CC' Key3
C EVAL *IN02 = '1'
C EVAL *IN03 = '0'
C Full_Kl SETLL Rec1 90 *
* The CHAIN operation below will retrieve a record with 'JJ' in Key1,
* 'KK' in Key2, and a null Key3. Again, because *IN03 is ON, even
* if the programmer had moved some value (say 'XX') into the search
* argument for Key3, 'XX' will not be used. This means if File1
* actually has a record with a key 'JJKKXX', that record will not
* be retrieved.
*
C MOVE 'JJ' Key1
C MOVE 'KK' Key2
C EVAL *IN02 = '0'
C EVAL *IN03 = '1'
C Full_Kl CHAIN Rec1 80
*
* The CHAIN operation below uses a partial key as the search argument.
* It will retrieve a record with 'NN' in Key1, a null key2, and any
* value including a null value in Key3.
*
* In the database, the NULL value occupies the highest position in
* the collating sequence. Assume the keys in File1 are in ascending
* sequence. If File1 has a record with 'NN??xx' as key (where ??
* means NULL and xx means any value other than NULL), that record
* will be retrieved. If such a record does not exist in File1, but
* File1 has a record with 'NN????' as key, the 'NN????' record will
* be retrieved. The null flags for Key2 and Key3 will be set ON
* as a result.
*
C MOVE 'NN' Key1
C SETON 05
C Partial_Kl CHAIN Rec1 70