Access Query LanguageAccess Query Language overview

Access Query Language overview

AQL uses TCL commands and displays the results either on terminals or printers. AQL operates on specified files and items based on various optional criteria, specifications, modifiers, limiters, and options.

FlashBASIC calls from dictionaries are used for complex data calculations and output formatting.

The use of B-tree indexes increases the speed and performance of AQL.

AQL sentences are entered at TCL and can be recalled, modified, or executed through the use of the tcl-stack. AQL sentences can also be stored and invoked through macros, menus, Procs, and FlashBASIC (using the execute statement).

See also

*a0-a13, *a9998, *a9999, any modifier, Attribute, B-tree, count command, execute statement, FlashBASIC and BASIC differences, list command, list-item command (Access Query Language), macro attribute, output-macro, paint command, Selection criteria, Processing codes (Update processor), ss modifier, Options (Access Query Language), u1209 user exit, update command

  • AQL sentence form
    In an AQL sentence, the command and file reference are required. The AQL command must be the first word of the sentence. All other elements are optional and are used to modify either the operator, operand, or output.
  • AQL command categories
    AQL commands essentially break down into these categories:
  • Default attribute items (Access Query Language)
    Default attribute items have numeric item-IDs starting with 1.
  • Default output specifications
    In addition to explicitly listing attribute names as part of the AQL sentence, there are three features that can be used to specify default output specifications.
  • File reference (Access Query Language)
    A file reference is a standardized mechanism for designating a particular file within D3.
  • Item list
    The item list specifies one or more item-IDs in the file defined by the associated file reference.
  • Modifiers
    Modifiers control listing parameters such as double-spacing (dbl-spc), control breaks (roll-on or break-on), column totals (total), and suppression of item-IDs (id-supp), automatic headings (hdr-supp or col-hdr-supp), and default messages (ni-supp).
  • Options (Access Query Language)
    Options are used to alter the behavior of AQL sentences.
  • Output specifications
    Output specifications specify the attributes to list.
  • Print limiters
    Print limiters suppress the listing of attributes within an item that do not meet specified limits.
  • Retrieval of items from files
    The AQL processor uses both the master dictionary and the file dictionary to determine the definition of the elements in the AQL sentence. The pointer to the file dictionary and the connectives used in the sentence, for example, are found in the master dictionary. The file pointer to the data file and file-specific attribute definitions are found in the file dictionary.
  • Selection criteria
    Selection criteria determines which items are to be processed by AQL and is designated by the with or if modifiers. Without any selection clauses in an AQL sentence, every item in the file is eligible for processing.
  • Sort criteria
    A sort criteria defines the AQL collation sequence. The sort is invoked by the by, by-dsnd, by-exp, or by-exp-dsnd modifiers in a left-to-right order to determine the order in which items are processed by AQL. There is no limit to the number of sort keys within an AQL sentence.
  • Temporary attribute items
    Attribute items using special attribute names can be specified in an AQL sentence without actually existing in either the file dictionary or the account master dictionary.
  • Throwaway connectives
    Throwaway connectives are a class of AQL modifiers that have no effect on command execution.

Related topics
Access Query Language
AQL commands
AQL modifiers
AQL relational operators and logical clauses
Phrases
AQL user exits