MI_DATUM mi_qual_constant(MI_AM_QUAL_DESC *qualDesc);

qualDesc

points to the qualification descriptor.

To retrieve the constant value from the argument lists of a qualification function, call mi_qual_constant() from the am_beginscan or am_getnext purpose function.

Qualification functions evaluate the contents of a column against some criteria, such as a supplied constant value.

If a qualification function does not involve a host variable, mi_qual_constant() retrieves the explicit constant argument. For example, mi_qual_constant() retrieves the string harry from the arguments to the following function:

WHERE equal(name,'harry')

If a qualification function involves a host variable but no explicit value, mi_qual_constant() retrieves the runtime constant value that is associated with the host variable. For example, mi_qual_constant() retrieves the runtime value that replaces the ? in the following function:

WHERE equal(name,? )

To determine if a function involves a host variable argument, execute mi_qual_const_depends_hostvar() in the am_scancost purpose function. If mi_qual_const_depends_hostvar() returns MI_TRUE, call mi_qual_constant() from am_getnext to retrieve the most recent value for the host variable and do not save the value from mi_qual_constant() in user data for subsequent scans.

The MI_DATUM structure contains the value of the constant argument.

See the descriptions of:

• Functions mi_qual_column(), mi_qual_constisnull(), and mi_qual_const_depends_hostvar()
• Generic functions in Table 9
• MI_DATUM in the IBM Informix: DataBlade API Programmer's Guide