| Navigation: Language Reference > 4 - Entity Declarations > File Structures >====== KEY (declare dynamic file access index) ====== |    |
| label | KEY([-/+]field,…,[-/+][field]) [,DUP] [,NAME( )] [,NOCASE] [,OPT] [,PRIMARY] |
| label | The label of the KEY (PROP:Label). |
| KEY | Declares a dynamically maintained index into the data file. |
| -/+ | The - (minus sign) preceding a key component field specifies descending order for that component. If omitted, or + (plus sign), the component is sorted in ascending order. |
| field | The label of a field in the RECORD structure of the FILE in which the KEY is declared. The field is a key component. A field declared with the DIM attribute (an array) may not be used as a key component. |
| NAME | Specifies the disk file specification of the KEY (PROP:NAME). |
| DUP | Allows multiple records with duplicate values in their key component fields (PROP:DUP). |
| NOCASE | Specifies case insensitive sort order (PROP:NOCASE). |
| OPT | Excludes, from the KEY, those records with null (zero or blank) values in all key component fields (PROP:OPT). |
| PRIMARY | Specifies the KEY is the file's relational primary key (a unique key containing all records in the file) (PROP:PRIMARY). |
A KEY is an index into the data file which is automatically updated whenever records are added, changed, or deleted. It is used to access records in a different logical order than the “physical order” of the file. A KEY may be used for either sequential file processing or direct random access.
A KEY may have more than one component field. The order of the components determines the sort sequence of the key. The first component is the most general, and the last component is the most specific. Generally, a data file may have up to 255 keys (and indexes) and each key may be up to 255 bytes, but the exact numbers are file driver dependent.
Example:
Names FILE,DRIVER('Clarion'),PRE(Nam)
NameKey KEY(Nam:Name),NOCASE,DUP !Declare the name key
NbrKey KEY(Nam:Number),OPT !Declare the number key
Rec RECORD
Name STRING(20)
Number SHORT
END
END
CODE
Nam:Name = 'Soft Velocity' !Initialize key field
GET(Names,Nam:NameKey) !Get the record
SET(Nam:NbrKey) !Set sequential by number
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