Interpreting the Scan Descriptor

The database server constructs a scan descriptor in response to a SELECT statement. The scan descriptor provides information about the key data types, as well as the locks and isolation levels that apply to the data that the query specifies.

As one of its primary functions, the scan descriptor stores a pointer to another opaque structure, the qualification descriptor that contains WHERE-clause information. To access the qualification descriptor, use the pointer that the mi_scan_quals() function returns. A NULL-valued pointer indicates that the database server did not construct a qualification descriptor.

For more information about the information that scan descriptor provides, refer to Scan Descriptor and the scan-descriptor accessor functions that begin on page mi_scan_forupdate().