Use Open Query File (OPNQRYF) command

The Open Query File (OPNQRYF) command is a control language (CL) command that allows you to perform many data processing functions on database files. These topics discuss how to create a query using the OPNQRYF command, how to specify parameters for its major functions, and how to use it with your high-level language program.

Essentially, the OPNQRYF command acts as a filter between the processing program and the database records. The database file can be a physical or logical file. Unlike the Create Physical File (CRTPF) or Create Logical File (CRTLF) command, the OPNQRYF command creates only a temporary file for processing the data; it does not create a permanent file.

The OPNQRYF command has functions similar to those in data description specifications (DDS) and the CRTPF and CRTLF commands. DDS requires source statements and a separate step to create the file. The OPNQRYF command allows a dynamic definition without using DDS. The OPNQRYF command does not support all of the DDS functions, but it supports significant functions that go beyond the capabilities of DDS. In addition, Query for iSeries™ can be used to perform some of the function the OPNQRYF command performs. However, the OPNQRYF command is more useful as a programmer's tool.

The OPNQRYF command parameters also have many functions similar to the SQL SELECT statements. For example, the FILE parameter is similar to the SQL FROM statement, the QRYSLT parameter is similar to the SQL WHERE statement, the GRPFLD parameter is similar to the SQL GROUP BY statement, and the GRPSLT parameter is similar to the SQL HAVING statement.

To understand the OPNQRYF command, you must be familiar with its two processing approaches: using a format in the file, and using a file with a different format. The typical use of the OPNQRYF command is to select, arrange, and format the data so it can be read sequentially by your high-level language program.

• Create a query with the Open Query File (OPNQRYF) command
  To create a query, you can use the Open Query File (OPNQRYF) command. Alternatively, you can create a query using the Run SQL Scripts window in iSeries Navigator.
• Use an existing record format in the file
  The Open Query File (OPNQRYF) command does the record selection and your program processes only the records that meet the selection values. You can use this approach to select a set of records, return records in a different sequence than they are stored, or both.
• Use a file with a different record format
  For more advanced functions of the Open Query File (OPNQRYF) command (such as dynamically joining records from different files), you must define a new file that contains a different record format.
• CL program coding with the Open Query File (OPNQRYF) command
  The Open Query File (OPNQRYF) command has these basic rules that can prevent coding errors.
• The zero-length literal and the contains (*CT) function
  In the Open Query File (OPNQRYF) command, a zero-length literal is denoted as a quoted string with nothing, not even a blank, between the quotation marks (""). Zero-length literal support changes the results of a comparison when used as the compare argument of the contains (*CT) function.
• Usage notes for Open Query File (OPNQRYF) command
  These usage notes pertain to the examples in the topics that describe how to specify the parameters for the major functions of the Open Query File (OPNQRYF) command and how to use the OPNQRYF command with your high-level language program.
• Select records without using DDS
  Dynamic record selection allows you to request a subset of the records in a file without using data description specifications (DDS).
• Considerations for creating a file and using the FORMAT parameter
  This topic discusses the considerations for creating a file and using the FORMAT parameter.
• Considerations for arranging records
  This topic discusses the considerations for using the Open Query File (OPNQRYF) command to arrange records.
• Considerations for distributed data management files
  The Open Query File (OPNQRYF) command can process distributed data management (DDM) files, however, there are certain considerations.
• Considerations for writing a high-level language program
  There are certain considerations for writing a high-level language program.
• Messages sent when the Open Query File (OPNQRYF) command is run
  When the Open Query File (OPNQRYF) command is run, messages are sent informing the interactive user of the status of the OPNQRYF request. For example, if a keyed access path is built by the OPNQRYF command to satisfy the request, a message is sent to the user.
• Use the Open Query File (OPNQRYF) command for more than just input
  The Open Query File (OPNQRYF) command supports the OPTION parameter to determine the type of processing. The default is OPTION(*INP), so the file is opened for input only. You can also use other OPTION values on the OPNQRYF command and a high-level language program to add, update, or delete records through the open query file.
• Compare date, time, and timestamp using the Open Query File (OPNQRYF) command
  A date, time, or timestamp value can be compared either with another value of the same data type or with a string representation of that data type.
• Perform date, time, and timestamp arithmetic using the Open Query File (OPNQRYF) command
  Date, time, and timestamp values can be incremented, decremented, and subtracted. These operations might involve decimal numbers called durations. These topics include a definition of durations and a specification of the rules for performing arithmetic operations on date, time, and timestamp values.
• Use the Open Query File (OPNQRYF) command for random processing
  You can use the Open Query File (OPNQRYF) command for sequential processing. You can also use the OPNQRYF command for random processing.
• Open Query File (OPNQRYF) command: Performance considerations
  Here are tips and techniques for optimizing the performance when you use the Open Query File (OPNQRYF) command.
• Open Query File (OPNQRYF) command: Performance considerations for sort sequence tables
  Here are tips and techniques for optimizing the performance of sort sequence tables.
• Performance comparisons with other database functions
  The Open Query File (OPNQRYF) command uses the same database support as logical files and join logical files. Therefore, the performance of functions like building a keyed access path or doing a join operation is the same.
• Field use
  When the grouping function is used, all fields in the record format for the open query file (FORMAT parameter) and all key fields (KEYFLD parameter) must be either grouping fields (specified on the GRPFLD parameter) or mapped fields (specified on the MAPFLD parameter).
• Files shared in a job
  In order for your application program to use the open data path built by the Open Query File (OPNQRYF) command, your program must share the query file. If your program does not open the query file as shared, then it actually does a full open of the file it was originally compiled to use (not the query open data path built by the OPNQRYF command).
• Checking if the record format description changed
  If record format level checking is indicated, the format level number of the open query file record format (identified on the FORMAT parameter) is checked against the record format your program was compiled against. This occurs when your program shares the previously opened query file.
• Other runtime considerations for the Open Query File (OPNQRYF) command
  Read other runtime considerations for the Open Query File (OPNQRYF) command, including overrides and copying from an open query file.
• Typical errors when using the Open Query File (OPNQRYF) command
  You must specify several functions correctly for the Open Query File (OPNQRYF) command and your program to get the correct results.
• Open data path considerations
  This topic outlines the considerations for the open data path (ODP).
• Field names
  Listed here are the requirements for specifying field names on the Open Query File (OPNQRYF) command parameters.
• Expressions
  This topic discusses the conventions for the expressions specified on the Open Query File (OPNQRYF) command.
• Built-in functions
  The built-in functions listed here are supported for the expression used to define a derived field on the MAPFLD parameter or a complex selection operand specified on the QRYSLT or GRPSLT parameter.
• Restricted built-in functions
  Listed here are several restricted built-in functions.