The SELECT command creates a temporary select-list of file items to be processed by the next TCL or INFO/ACCESS statement, or by other processors such as the Editor, mvBASIC, or PROC. Creating a select-list is a useful way to define and operate on a subset of items in a database.
Format
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SELECT [DICT] filename [item-list] [selection] [output] |
Parameter(s)
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DICT |
Specifies the file dictionary. |
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filename |
Name of the file. |
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item-list |
List of individual item-IDs that you want to select or compare against specified criteria. Enclose each item-ID in single quotes. If you do not specify an item-list, the SELECT command selects all items in filename. |
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selection |
Specifies one or more conditions that an item must meet to be included in the select-list. For a complete description of selection expression syntax, see the LIST Command. |
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output |
Name of an attribute whose values are to be selected. Each value becomes a separate item-ID in the select-list. |
Description
The SELECT command creates a temporary select-list containing item-IDs of the items specified in the item-list or the selection criteria. The items referenced by the select-list are processed by the next command you execute. For instance, before invoking the Editor you might create a select-list as a way of specifying which items you want to edit.
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CAUTION |
Only the statement immediately following the SELECT statement has access to the select-list. In other words, you must use the select-list immediately, or you will lose it! |
To permanently save the select-list, use the SAVE-LIST command. Once a select-list is saved, you can retrieve it at any time with the GET-LIST command.
A select-list can reference data in any file, not just the file specified in the original SELECT statement. If two files have similar items with the same item-IDs, you can create a select-list from one file, then use it to operate on items from the other file.
Creating a Select-list
The following example illustrates how to create a select-list from one file and use it to access data in another file.
Assume a file called CUSTOMER.INACTIVE contains the item-IDs of customers with inactive accounts. You can create a select-list of these item-IDs and then retrieve the customers’ names and addresses from the CUSTOMERS file:
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>SELECT CUSTOMERS.INACTIVE 41 ITEMS SELECTED. >LIST CUSTOMERS LAST-NAME FIRST-NAME STREET CITY STATE . . . |
The next example creates a select-list of dictionary items that define attribute 3 of the ORDERS file. Once the select-list has been created, the Editor is used to display the first item selected:
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>SELECT DICT ORDERS WITH A/AMC = 3
3 ITEMS SELECTED. >ED DICT ORDERS TITLE TOP .P 001 S 002 1 003 004 005 006 007 008 TBOOK-CATALOG;C;;2 009 T 010 35 EOI 010 . |