SPI_cursor_open
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## SPI_cursor_open

SPI_cursor_open — set up a cursor using a statement created with `SPI_prepare`

## Synopsis

    Portal SPI_cursor_open(const char * name, SPIPlanPtr plan,
                           Datum * values, const char * nulls,
                           bool read_only)

## Description

`SPI_cursor_open` sets up a cursor (internally, a portal) that will execute a statement prepared by `SPI_prepare`. The parameters have the same meanings as the corresponding parameters to `SPI_execute_plan`.

Using a cursor instead of executing the statement directly has two benefits. First, the result rows can be retrieved a few at a time, avoiding memory overrun for queries that return many rows. Second, a portal can outlive the current C function (it can, in fact, live to the end of the current transaction). Returning the portal name to the C function's caller provides a way of returning a row set as result.

The passed-in parameter data will be copied into the cursor's portal, so it can be freed while the cursor still exists.

## Arguments

`const char * `name``

  name for portal, or `NULL` to let the system select a name

`SPIPlanPtr `plan``

  prepared statement (returned by `SPI_prepare`)

`Datum * `values``

  An array of actual parameter values. Must have same length as the statement's number of arguments.

`const char * `nulls``

  An array describing which parameters are null. Must have same length as the statement's number of arguments.

  If `nulls` is `NULL` then `SPI_cursor_open` assumes that no parameters are null. Otherwise, each entry of the `nulls` array should be `' '` if the corresponding parameter value is non-null, or `'n'` if the corresponding parameter value is null. (In the latter case, the actual value in the corresponding `values` entry doesn't matter.) Note that `nulls` is not a text string, just an array: it does not need a `'\0'` terminator.

`bool `read_only``

  `true` for read-only execution

## Return Value

Pointer to portal containing the cursor. Note there is no error return convention; any error will be reported via `elog`.

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