Caché SQL Reference
NVL
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A function that tests for NULL and returns the appropriate expression.
Synopsis
NVL(check-expression,replace-expression)
Arguments
check-expression The expression to be evaluated.
replace-expression The expression that is returned if check-expression is NULL.
Description
NVL evaluates check-expression and returns one of two values:
The arguments check-expression and replace-expression can have any data type. If their data types are different, Caché converts replace-expression to the data type of check-expression before comparing them. The data type of the return value is always the same as the data type of check-expression, unless check-expression is character data, in which case the return value’s data type is VARCHAR2.
Note that NVL is supported for Oracle compatibility, and is the same as the ISNULL function.
Refer to NULL section of the “Language Elements” chapter of Using Caché SQL for further details on NULL handling.
NULL Handling Functions Compared
The following table shows the various SQL comparison functions. Each function returns one value if the comparison tests True (A equals B) and another value if the comparison tests False (A not equal to B):
SQL Function Comparison Test Return Value
NULLIF expression1 = expression2
True = NULL
False = expression1
IFNULL (2 argument form) expression1 = NULL
True = expression2
False = NULL
COALESCE expression1 = NULL, expression2 = NULL, ...
True = test expression2
False = expression1
ISNULL expression1 = NULL
True = expression2
False = expression1
NVL expression1 = NULL
True = expression2
False = expression1
IFNULL (3 argument form) expression1 = NULL
True = expression2
False = expression3
Example
This following example returns the replace-expression (99) because the check-expression is NULL:
SELECT NVL(NULL,99) AS NullTest
 
This following example returns the check-expression (33) because check-expression is not NULL:
SELECT NVL(33,99) AS NullTest
 
The following Dynamic SQL example returns the string 'No Preference' if FavoriteColors is NULL; otherwise, it returns the value of FavoriteColors:
  ZNSPACE "SAMPLES"
  SET myquery=3
    SET myquery(1)="SELECT Name,"
    SET myquery(2)="NVL(FavoriteColors,'No Preference') AS ColorChoice "
    SET myquery(3)="FROM Sample.Person"
  SET tStatement = ##class(%SQL.Statement).%New()
  SET qStatus = tStatement.%Prepare(.myquery)
    IF qStatus'=1 {WRITE "%Prepare failed:" DO $System.Status.DisplayError(qStatus) QUIT}
  SET rset = tStatement.%Execute()
  DO rset.%Display()
  WRITE !,"End of data"
 
See Also