!!!Comparison of Null Values

Any column that does not have a value is known as being "NULL or UNKNOWN" and whenever you compare anything to a [Null value|NULL] the result will always be false (down the ELSE path).  Also important to note is that NULL is not equal to another NULL, nor is it "not equal" - it is unknown.

To work around this you need detect when a column has a Null value and initialize it.

In this workflow usercalc, we want to see when a value has changed in a given field.  The easy solution is to test new value against old value like this:

|5000 |IF |NV |EID.DRIVERS_LICENSE |EQ |OV |EID.DRIVERS_LICENSE | | | 5100 |5500

If either the new value (NV) or old value (OV) are NULL, the condition will be false and you will always go down the else branch - even when they are both NULL.  To deal with this scenario, we have to use some variables (recommended to be character type) and additional logic using the [EQNL|EQNL_OPERATOR] operator.

|5000 |LET  |V  |NV_DL  |EQNL   |NV   |EID.DRIVERS_LICENSE   |A  | No Value |5010  |
|5010 |LET  |V  |OV_DL  |EQNL   |OV   |EID.DRIVERS_LICENSE   |A  | No Value |5020  |
|5020 |IF   |V  |NV_DL  |EQ     |V    |OV_DL                 |   |          |5100  | 5500


When using this technique you must always use a value (in this case the alpha "No Value" that would never actually be in the field you are comparing to in order to correctly check that there was a change occurring.


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![Notes|Edit:Internal.COMPARISON+OF+NULL+VALUES] 	
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