IMS DB Command Codes

Command codes are special one-letter modifiers that can be included in SSAs to alter the behavior of DL/I calls, providing more control and efficiency in database operations. Command codes are single-character instructions that modify how DL/I processes a call. By incorporating command codes into SSAs, you can:

• Reduce the number of DL/I calls needed.
• Retrieve multiple segments in a single call.
• Control the position and parentage in the database hierarchy.
• Manage concurrent access to segments.​

Incorporating Command Codes into SSAs:

To include a command code in an SSA:

• Insert an asterisk '*' in the 9th position immediately after the segment name.
• Follow the asterisk with the desired command code(s).
• Unqualified SSA: The command code is followed by a space. Format -
  

  01 QUALIFIED-SSA.
     05 SEGMENT-NAME  PIC X(8).
     05 FILLER        PIC X VALUE '*'.
     05 COMMAND-CODE  PIC X.
     05 FILLER        PIC X.

• Qualified SSA: The command code is followed by a left parenthesis (. Format -
  

  01 QUALIFIED-SSA.
     05 SEGMENT-NAME  PIC X(8).
     05 FILLER        PIC X VALUE '*'.
     05 COMMAND-CODE  PIC X.
     05 FILLER        PIC X     VALUE '('.
     05 FIELD-NAME    PIC X(8).
     05 REL-OPR       PIC X(2).
     05 SEARCH-VALUE  PIC X(n).
     05 FILLER        PIC X     VALUE ')'.

Common Command Codes:

Code	Name	Description
C	Concatenated Key	Allows access to a segment by specifying a concatenated key of all parent segments. Useful when all higher-level keys are known.
D	Path Call.	Retrieve the segment and all its dependents.
F	First occurrence of the segment	Allows access to a segment by specifying a concatenated key of all parent segments. Useful when all higher-level keys are known.
L	Last occurrence of the segment	Retrieves the last occurrence of a segment type. Often used with GN or GNP calls.
N	Path Call Ignore. Suppress replacement of higher-level segments	Used with D command to prevent replacement of higher-level segments during a path call.
P	Set Parentage. Establish parentage at a higher level	Establishes parentage at a higher level segment rather than the lowest level segment retrieved.
Q	Enqueue Segment. Enqueue the segment to prevent concurrent access	Prevents other programs from accessing a segment until the current program reaches a commit point.
U	Maintain position at the current level	Maintains the current position at a specific level in the hierarchy during retrieval.
V	Maintain parentage at current and higher levels	Maintains the current position at the specified level and all higher levels.
.	Null Command Code	Placeholder indicating no command code is used. Useful for dynamic command code assignment.

Examples:

Scenario1 - Qualified SSA: To retrieve the last occurrence of the "EMPLOYEE" segment:

01 QUALIFIED-SSA.
   05 SEGMENT-NAME  PIC X(8) VALUE 'EMPLOYEE'.
   05 FILLER        PIC X     VALUE '*'.
   05 CMD-CODE      PIC X     VALUE 'L'.
   05 FILLER        PIC X     VALUE '('.
   05 FIELD-NAME    PIC X(8) VALUE 'EMPID  '.
   05 REL-OPR       PIC X(2) VALUE 'EQ'.
   05 SEARCH-VALUE  PIC X(5) VALUE '12345'.
   05 FILLER        PIC X     VALUE ')'.

Scenario2 - Unqualified SSA: To retrieve the first occurrence of the EMPLOYEE segment:

01 QUALIFIED-SSA.
   05 SEGMENT-NAME  PIC X(8) VALUE 'EMPLOYEE'.
   05 FILLER        PIC X     VALUE '*'.
   05 CMD-CODE      PIC X     VALUE 'L'.
   05 FILLER        PIC X     VALUE ' '.

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