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NULL Predicate
A NULL predicate determines whether a primary has the value NULL. The
predicate evaluates to true if the primary is NULL. If the NOT option is
used, the predicate evaluates to true if the primary is not NULL.
Scope
SQL Data Manipulation Statements
SQL Syntax
{ColumnName }
{:HostVariable [[INDICATOR] :IndicatorVariable]}
{? }
{:LocalVariable }
{:ProcedureParameter }
{::Built-inVariable }
{AddMonthsFunction }
{AggregateFunction } IS [NOT] NULL
{Constant }
{ConversionFunction }
{CurrentFunction }
{LongColumnFunction }
{StringFunction }
{TIDFunction }
{(Expression) }
Parameters
ColumnName is the name of a column from which a value is to
be taken; column names are defined in the "Names"
chapter.
HostVariable contains a value in an application program being
input to the expression.
IndicatorVariableames an indicator variable,
whose value determines whether
the associated host variable
contains a NULL value:
> = 0 the value is not NULL
< 0 the value is NULL (The
value in the host
variable will be
ignored.)
? is a place holder for a dynamic parameter in a
prepared SQL statement in an application program.
The value of the dynamic parameter is supplied at
run time.
LocalVariable contains a value in a procedure.
ProcedureParameter contains a value that is passed into or out of a
procedure.
Built-inVariable is one of the following built-in variables used
for error handling:
* ::sqlcode
* ::sqlerrd2
* ::sqlwarn0
* ::sqlwarn1
* ::sqlwarn2
* ::sqlwarn6
* ::activexact
The first six of these have the same meaning that
they have as fields in the SQLCA in application
programs. Note that in procedures, sqlerrd2
returns the number of rows processed for all host
languages. However, in application programs,
sqlerrd3 is used in COBOL, Fortran, and Pascal,
while sqlerr2 is used in C. ::activexact
indicates whether a transaction is in progress or
not. For additional information, refer to the
application programming guides and to the chapter
"Constraints, Procedures, and Rules."
AddMonthsFunction returns a value that represents a DATE or
DATETIME value with a certain number of months
added to it.
AggregateFunction is a computed value; aggregate functions are
defined in this chapter.
Constant is a specific value; constants are defined later
in this chapter.
ConversionFunction returns a value that is a conversion of a
date/time data type into an INTEGER or CHAR
value, or from a CHAR value.
CurrentFunction returns a value that represents the current DATE,
TIME, or DATETIME.
LongColumnFunction returns information from a long column
descriptor.
StringFunction returns a partial value or attribute of string
data.
TIDFunction returns the database address of a row (or rows
for a BULK SELECT) of a table or an updatable
view. You cannot use mathematical operators with
this function except to compare it to a value,
host variable, or dynamic parameter (using =, or
<>) .
(Expression) is one or more of the above primaries, enclosed
in parentheses.
NOT reverses the value of the predicate that follows
it.
Description
The primary may be of any data type except LONG BINARY or LONG VARBINARY.
Example
Vendors with no personal contact named are identified.
SELECT *
FROM PurchDB.Vendors
WHERE ContactName IS NULL