The mi_qual_constisnull_nohostvar() accessor function
The mi_qual_constisnull_nohostvar() function determines whether a qualification-function argument list contains an explicit NULL value.
Syntax
mi_boolean
mi_qual_constisnull_nohostvar(MI_AM_QUAL_DESC *qualDesc);- qualDesc
- Points to the qualification descriptor.
Usage
The mi_qual_constisnull_nohostvar() function evaluates the explicit value, if any, that the WHERE clause specifies in the function argument list. This function does not evaluate host variables. Call this function from the am_scancost purpose function.
The following functions compare a column
that contains a row to a row constant. Each function depends on a
client application to provide part or all of the constant value. The Return value column shows the results of the mi_qual_constisnull_nohostvar() function.
| Sample function | Description | Return value |
|---|---|---|
| function(column, row(10,?,20)) | The row contains the explicit constant values 10 and 20. The unknown value that replaces ? does not influence the return value of mi_qual_constisnull_nohostvar(). | MI_FALSE |
| function(column, row(NULL,?,20)) | The first field in the row constant specifies an explicit NULL value. | MI_TRUE |
| function(column,?) | The arguments to the function contain no explicit values. The qualification descriptor contains a NULL in place of the missing explicit value. | MI_TRUE |
Return values
- MI_TRUE
- Indicates one of the following conditions in the argument list:
- An explicit NULL-valued constant
- No explicit values
- MI_FALSE
- Indicates that the constant argument is not NULL-valued.
Related topics
See the description of:
- Host variables in the Informix® DataBlade® API Programmer's Guide