Microsoft KB Archive/135753

= Implications of Using NULL in Data Validation Rules =

Article ID: 135753

Article Last Modified on 2/15/2000

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APPLIES TO


 * Microsoft Visual FoxPro 3.0 Standard Edition

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This article was previously published under Q135753



SUMMARY
Because Data Validations are expressions, NULL values inserted into fields and passed to Data Validation expressions behave in a consistent manner with that of other expressions. If the Data Validation for a field resolves to True (.T.) or False (.F.) with a NULL value, that logical result is accepted. In many cases, the expression will evaluate to NULL (For example, NULL > 1000). In this case, because the expression returns NULL, not True or False, it is rejected.



Step-by-Step Example
 Create a program called Myprog.prg  Type in the following code segment: CREATE DATABASE mydata1 CREATE TABLE mytable (lastname c(20) NULL, firstname c(20) NULL, ;     city c(20) NULL CHECK city>"a") INSERT INTO mytable (lastname,firstname,city) ; VALUES ("Ansarti","Jim","San Jose") INSERT INTO mytable (lastname,firstname,city) ; VALUES ("Hayden","Rance",.NULL.) INSERT INTO mytable (lastname,firstname,city) ; VALUES ("Putnam","Phil","New Orleans")  Save the program.  In the Command window, type: DO Myprog.prg  The program executes, and the INSERT command with city equal to .NULL. generates the error message, "Field City Validation rule is violated."

Additional query words: 3.00 VFoxWin

Keywords: KB135753

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