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Version 1.9 Build 1556

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taqlwidget - Tool

	Package	display
	Module	widgets

Postscript file available

Widget to form a TaQL command

include "taqlwidget.g"

Description

The Table Query Language (TaQL) is an SQL-like language for defining commands to do selections and/or sorts on an AIPS++ table. It offers a lot of power and flexibility, but the syntax is not always clear. Furthermore, the names and data types of the columns in the table might not be known. This makes it sometimes hard to create a query command.

The TaQL widget is a Query-By-Example like widget to assist the user in creating a TaQL command. Such a command consists of four optional parts. Constructor arguments control if the user can specify these parts by enabling the appropriate parts of the widget.

• The select-list tells which columns to select from the table.
  A check box for each column name lets the user define the select-list. Pressing a button means that the column is added to the select-list in the entry box at the bottom. Pressing again removes it. It is also possible to edit the select-list directly.
  Note that an empty select-list means that all columns are selected.
• The where-expression tells which rows to select from the table.
  This part of the widget is always active and is meant to ease the process of creating the where-expression. The available columns and, if applicable, lists of possible values are shown in a form. The popuphelp shows the data type, etc.. The user can fill in the form to create (part of) the where-expression. Special buttons are available to create more complex where-expressions with parentheses and AND, OR, and NOT operators by combining the current contents of the form with the where-expression already present in the entry box at the bottom. It is also possible to edit the where-expression in the entry box directly.
  The expand button is only giving information. Pressing it shows how the current contents of the form convert to a where-expression
• The sort-list tells if and how the resulting table is sorted.
  A listbox is shown for each column to let the user add or remove the column to the sort-list in the entry box at the bottom. The user can choose No Sort, Ascending, or Descending. The No Sort choice removes the column from the sort-list. It is also possible to edit the sort-list directly.
• The giving entry box lets the user specify the name of the resulting table. No name means that the result is transient.

All these parts can be filled in manually, but it is easier to use the form at the top. It shows all available fields and if appropriate also a check box to tell if the field has to added to select list. It can also have a sort menu to add the field to the sort list.
Each field is followed by an operator menu and an entry box which can be used to fill in values. Multiple values are possible separated by commas. When a field can only have a limited set of values, the entry box is preceeded by a menu from which the user can select values. Fields of type string have some extra operators to compare the field with a regular expression (or filename-like pattern). It also has an option menu to make tell if case has to be ignored (default no) and if the string has to be enclosed in quotes (default yes). Note that in a TaQL command an unquoted string is treated as the name of another field.

To make the widget appear less overwhelming, the more advanced features (like the OR button and the resulting entry boxes) are hidden in a rollup. The rollup also has an expand button to show what the TaQL string looks like for the current contents of the form.

Constructing the widget is driven by the description of the table columns as given by the table function getdesc().
However, use of the widget is not limited to tables. As long as a correct description is given, the widget can be used to create query commands for other purposes as well.