4.7 Where are the Operators?

    What functions can be used - to concatenate fields, to convert data, to check for errors? Two simple and powerful features of RES-Reach make them mostly unnecessary: recursive evaluation of variables and nested SQL queries.

    Rather than inventing a new set of functions and operators for you, you can use the ones you are most familiar with: the ones from your favourite database language. Simply put the operation into the SQL element of a DATA tag, and your results are available as a virtual database field. For example: 

    
<DATA SQL="SELECT TOP 1 (ISDATE('{Date1}')) AS VAL1, (ISDATE('{Date2}')) AS VAL2, (VAL1 AND VAL2) AS ALL_VALID FROM Dummy;", DATABASE="dummy.mdb", CONNECT="", MODE="READONLY", ALIAS="Valid">
<RECORD>
    <IF VARIABLE="{[Valid.ALL_VALID]}" OPERATOR="NE" COMPARISON="0">
        <!-- All fields are OK -->
        ...
    </IF>
</RECORD>
</DATA>

    Another method is to use string concatenation to test for values. For instance: 

    
<IF VARIABLE=";{Fld1};" OPERATOR="SS" COMPARISON=";;0;{Unknown};">
    <![ Fld1 is not valid ]>
    ...
</IF>

    Yet another is to use recursive evaluation of variables. For instance, suppose that you have the following constants defined in the [VARIABLES] section of the NETBASE.INI file: 

    CHECKED:-0=

    CHECKED:-1=CHECKED

    You can concatenate a variable that evaluates to a boolean value (‘0’ or ‘1’) to the string "CHECKED:-" to determine which of the two variables will be replaced into the tag: the empty string or the one that says "CHECKED": 

    <INPUT TYPE="CHECKBOX" NAME="Box1" {CHECKED:-{[Currently_Selected]}}>

    A note of caution: make sure that your user can not send a full variable name as a string that is then recursively evaluated; a malicious user could then get read or write access to variables or fields to which you did not intend to allow access. There are a number of features in the parser that limit the degree to which this type of syntax may be used.