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IFNULL

A function that tests for NULL and returns the appropriate expression.

Synopsis

IFNULL(expression-1,expression-2 [,expression-3])
{fn IFNULL(expression-1,expression-2)}

Arguments

Argument Description
expression-1 The expression to be evaluated to determine if it is NULL or not.
expression-2 An expression that is returned if expression-1 is NULL.
expression-3 Optional — An expression that is returned if expression-1 is not NULL. If expression-3 is not specified, a NULL value is returned when expression-1 is not NULL.

The returned data type is described below.

Description

InterSystems IRIS supports IFNULL as both an SQL general function and an ODBC scalar function. Note that while these two perform very similar operations, they are functionally different. The SQL general function supports three arguments. The ODBC scalar function supports two arguments. The two-argument forms of the SQL general function and the ODBC scalar function are not the same; they return different values when expression-1 is not null.

The SQL general function evaluates whether expression-1 is NULL. It never returns expression-1:

  • If expression-1 is NULL, expression-2 is returned.

  • If expression-1 is not NULL, expression-3 is returned.

  • If expression-1 is not NULL, and there is no expression-3, NULL is returned.

The ODBC scalar function evaluates whether expression-1 is NULL. It either returns expression-1 or expression-2:

  • If expression-1 is NULL, expression-2 is returned.

  • If expression-1 is not NULL, expression-1 is returned.

Refer to NULL section of the “Language Elements” chapter of Using InterSystems SQL for further details on NULL handling.

Data Type of Returned Value

  • IFNULL(expression-1,expression-2): returns the data type of expression-2. If expression-2 is a numeric literal, a string literal, or NULL returns data type VARCHAR.

  • IFNULL(expression-1,expression-2,expression-3): if expression-2 and expression-3 have different data types, returns the data type with the higher (more inclusive) data type precedence. If expression-2 or expression-3 is a numeric literal or a string literal, returns data type VARCHAR. If expression-2 or expression-3 is NULL, returns the data type of the non-NULL argument.

    If expression-2 and expression-3 have different length, precision, or scale, IFNULL returns the greater length, precision, or scale of the two expressions.

  • {fn IFNULL(expression-1,expression-2)}: returns the data type of expression-1. If expression-1 is a numeric literal, a string literal, or NULL, returns data type VARCHAR.

DATE and TIME Display Conversion

Some expression-1 data types require conversion from Logical mode (mode 0) to ODBC mode (mode 1) or Display mode (mode 2). For example the DATE and TIME data types. If the expression-2 or expression-3 value is not the same data type, this value cannot be converted in ODBC mode or Display mode, and an SQLCODE error is generated: -146 for DATE data type; -147 for TIME data type. For example, IFNULL(DOB,'nodate',DOB) cannot be executed in ODBC mode or Display mode; it issue an SQLCODE -146 error with the %msg Error: 'nodate' is an invalid ODBC/JDBC Date value or Error: 'nodate' is an invalid DISPLAY Date value. To execute this statement in ODBC mode or Display mode, you must CAST the value as the appropriate data type: IFNULL(DOB,CAST('nodate' as DATE),DOB). This results in a date 0, which displays as 1840-12-31.

%List Display Conversion

A %List field is a string data type field with encoding. If expression-1 is a %List field, the appropriate expression-2 or expression-3 value depends on the Select Mode:

  • In Logical mode (mode 0) or Display mode (mode 2), a %List value is returned as string data type with the format $lb("element1","element2",...). Therefore, an expression-2 or expression-3 value must be specified as a %List, as shown in the following example:

      SET myquery=3
        SET myquery(1)="SELECT TOP 20 Name,"
        SET myquery(2)="IFNULL(FavoriteColors,$LISTBUILD('No Preference'),FavoriteColors) AS ColorChoice "
        SET myquery(3)="FROM Sample.Person"
      SET tStatement = ##class(%SQL.Statement).%New(2)  // 2=Display mode
      SET qStatus = tStatement.%Prepare(.myquery)
        IF qStatus'=1 {WRITE "%Prepare failed:" DO $System.Status.DisplayError(qStatus) QUIT}
      SET rset = tStatement.%Execute()
      DO rset.%Display()
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  • In ODBC mode (mode 1), a %List value is returned as a string of comma-separated elements: element1,element2,.... Therefore, an expression-2 or expression-3 value can be specified as a string as shown in the following example:

      SET myquery=3
        SET myquery(1)="SELECT TOP 20 Name,"
        SET myquery(2)="IFNULL(FavoriteColors'No Preference',FavoriteColors) AS ColorChoice "
        SET myquery(3)="FROM Sample.Person"
      SET tStatement = ##class(%SQL.Statement).%New(1)  // 1=ODBC mode
      SET qStatus = tStatement.%Prepare(.myquery)
        IF qStatus'=1 {WRITE "%Prepare failed:" DO $System.Status.DisplayError(qStatus) QUIT}
      SET rset = tStatement.%Execute()
      DO rset.%Display()
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NULL Handling Functions Compared

The following table shows the various SQL comparison functions. Each function returns one value if the logical comparison tests True (A same as B) and another value if the logical comparison tests False (A not same as B). These functions allow you to perform NULL logical comparisons. You cannot specify NULL in an actual equality (or non-equality) condition comparison.

SQL Function Comparison Test Return Value
IFNULL(ex1,ex2) [two-argument form] ex1 = NULL
True returns ex2
False returns NULL
IFNULL(ex1,ex2,ex3) [three-argument form] ex1 = NULL
True returns ex2
False returns ex3
{fn IFNULL(ex1,ex2)} ex1 = NULL
True returns ex2
False returns ex1
ISNULL(ex1,ex2) ex1 = NULL
True returns ex2
False returns ex1
NVL(ex1,ex2) ex1 = NULL
True returns ex2
False returns ex1
NULLIF(ex1,ex2) ex1 = ex2
True returns NULL
False returns ex1
COALESCE(ex1,ex2,...) ex = NULL for each argument
True tests next ex argument. If all ex arguments are True (NULL), returns NULL.
False returns ex

Examples

In the following example, the general function and the ODBC scalar function both returns the second expression (99) because the first expression is NULL:

SELECT IFNULL(NULL,99) AS NullGen,{fn IFNULL(NULL,99)} AS NullODBC
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In the following example, the general function and the ODBC scalar function examples return different values. The general function returns <null> because the first expression is not NULL. The ODBC example returns the first expression (33) because the first expression is not NULL:

SELECT IFNULL(33,99) AS NullGen,{fn IFNULL(33,99)} AS NullODBC
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The following Dynamic SQL example returns the string 'No Preference' if FavoriteColors is NULL; otherwise, it returns NULL:

  SET myquery=3
    SET myquery(1)="SELECT Name,"
    SET myquery(2)="IFNULL(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"
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The following Dynamic SQL example returns the string 'No Preference' if FavoriteColors is NULL; otherwise, it returns the value of FavoriteColors:

  SET myquery=3
    SET myquery(1)="SELECT Name,"
    SET myquery(2)="IFNULL(FavoriteColors,'No Preference',FavoriteColors) AS ColorChoice "
    SET myquery(3)="FROM Sample.Person"
  SET tStatement = ##class(%SQL.Statement).%New()
  SET tStatement.%SelectMode=2
  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"
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The following example returns the string 'No Preference' if FavoriteColors is NULL; otherwise, it returns the string 'Preference':

SELECT Name,
IFNULL(FavoriteColors,'No Preference','Preference') AS ColorPref
FROM Sample.Person
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The following ODBC syntax examples return the string 'No Preference' if FavoriteColors is NULL, otherwise they return the FavoriteColors data value:

SELECT Name,
       {fn IFNULL(FavoriteColors,$LISTBUILD('No Preference'))} AS ColorPref
FROM Sample.Person
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  SET myquery=3
    SET myquery(1)="SELECT Name,"
    SET myquery(2)="{fn IFNULL(FavoriteColors,'No Preference')} AS ColorChoice "
    SET myquery(3)="FROM Sample.Person"
  SET tStatement = ##class(%SQL.Statement).%New()
  SET tStatement.%SelectMode=1
  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"
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The following example uses IFNULL in the WHERE clause. It selects people under the age of 21 who do not have favorite color preferences. If FavoriteColors is NULL, IFNULL returns the Age field value, which is used for the condition test:

SELECT Name,FavoriteColors,Age
FROM Sample.Person
WHERE 21 > IFNULL(FavoriteColors,Age)
ORDER BY Age
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Refer to the NULL predicate (IS NULL, IS NOT NULL) for similar functionality.

See Also