When a DataBlade®
API statement-execution
function executes a query, the function must create a place to hold
the resulting rows. Each of these functions (mi_exec(), mi_exec_prepared_statement(),
or mi_open_prepared_statement()) automatically
creates a row cursor (often called a cursor). The row
cursor is an area of memory that serves as a holding place for rows
that the database server has retrieved.
The simplest way to hold the rows of a query is to use an implicit
cursor, which is defined with the following characteristics.
| Cursor characteristic |
Restriction |
| Read-only |
You can only examine the contents of the row
cursor. You cannot modify these contents. |
| Sequential |
A sequential cursor allows movement through
the rows of the cursor in the forward direction only. You cannot go
backward through the cursor. To re-access a row that you have already
accessed, you must close the cursor, reopen it, and move to the desired
row. |
Most
DataBlade®
API modules
can use an implicit cursor for accessing rows. However, if the cursor
characteristics of the implicit cursor are not adequate for the needs
of your
DataBlade®
API module,
you can define an explicit cursor with any of the following cursor
characteristics.
| Cursor characteristic |
Description |
| Cursor type |
In which direction does the cursor enable you
to access rows? You can choose a sequential cursor or a scroll cursor. |
| Cursor mode |
Which operations are valid on the rows in the
cursor? You can choose read-only or update mode. |
| Cursor lifespan |
How long does the cursor remain open? You can
choose whether to use a hold cursor. |
The following table shows how to choose a
DataBlade®
API statement-execution
function based on the type of cursor that the query requires.
| Can query use implicit cursor? |
DataBlade®
API function |
| Yes |
mi_exec(), mi_exec_prepared_statement() |
| No |
mi_open_prepared_statement() |
With the mi_open_prepared_statement() function,
you can specify an explicit cursor to hold the query rows. In addition,
you can assign a name to the cursor that you can use in other SQL
statements.