GenerateEqualsNull database parameter
Description
Specifies how DataWindows generates =null and <> null expressions
in retrieval arguments.
Controls
All database interfaces
Syntax
|
1 |
GenerateEqualsNull= '<span>value</span>' |
|
Parameter |
Description |
|---|---|
|
value |
|
Default
GenerateEqualsNull=’No’
Usage
When to use
When a DataWindow retrieves data from tables that contain
null columns, most DBMS interfaces expect expressions of the form, IS
NULL and IS NOT NULL. Expressions that
reference null data as values, such as Where column = NULL,
can cause the DBMS to reject the retrieval. For this reason, such
expressions in DataWindows are normally converted to the standard ANSI
syntax during retrieval.
If your DataWindow retrieves null data from a DBMS that supports expressions
of the =null or <> null form,
and you want to suppress the conversion of those expressions to
standard syntax, you can set the GenerateEqualsNull DBParm to true.
Examples
Consider these two statements:
|
1 |
SELECT "a1"."c1" FROM "a1" WHERE "a1"."c2" = :p1 |
|
1 |
SELECT "a1"."c1" FROM "a1" WHERE "a1"."c2" <> :p1 |
If GenerateEqualsNull is set to false, the statements are
generated as:
|
1 |
SELECT "a1"."c1" FROM "a1" WHERE "a1"."c2" is null |
|
1 |
SELECT "a1"."c1" FROM "a1" WHERE "a1"."c2" is not null |
If GenerateEqualsNull is set to true, the statements are generated
as:
|
1 |
SELECT "a1"."c1" FROM "a1" WHERE "a1"."c2" = null |
|
1 |
SELECT "a1"."c1" FROM "a1" WHERE "a1"."c2" <> null |