QUERY Function

Material prepared from GT.M Programmer’s Guide [BHASKAR2010]

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$QUERY(glvn)

Description

$QUERY takes a global variable array (“global”) glvn to scan for data values. A global is a persistent and dynamic tree containing text values.

; Configure a simple global, a tree with depth of 1 and only 2 branches
S ^X(0,1)="A"
S ^X(0,2)="B"
;
;  The global looks like this:
;
;       0
;     /   \
;    /     \
;  1="A"   2="B"
;
; To retrieve the values at each node in the global, use the QUERY function
;
; Call query on the global
SET Y=$QUERY(^X)
;
; Y is now ^X(0,1), and the value at this location can be retrieved
; with the Indirection Operator
WRITE !,@Y
; Output: A
;
; To get the next node, call query again with the value of the node at Y
SET Y=$QUERY(@Y)
WRITE !,@Y
; Output: B

Because the $QUERY function can be called not only with the original global but with the value of the global at a position, it can be repeatedly called using the Indirection Operator to traverse through the nodes of the tree.

; Configure a simple global, a tree with depth of 1 and only 2 branches
S ^X(0,1)="A"
S ^X(0,2)="B"
;
; Initialize Y for use with the Indirection Operator
SET Y="^X"
;
; Repeatedly use the QUERY function
;
FOR  SET Y=$QUERY(@Y) QUIT:Y=""  WRITE !,@Y
; Output: A
;         B

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