> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/server-programming/spi/spi-interface/spi-spi-cursor-open.md).

# SPI\_cursor\_open

### 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`.

***

原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/spi-spi-cursor-open.html)（英文原文，待翻譯）


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