---
title: "spi — Server Programming Interface features/examples"
id: contrib-spi
pg_version: "20devel"
---

<a id="contrib-spi"></a>

## F.43. spi — Server Programming Interface features/examples

The spi module provides several workable examples of using the [Server Programming Interface](spi.md) (SPI) and triggers. While these functions are of some value in their own right, they are even more useful as examples to modify for your own purposes. The functions are general enough to be used with any table, but you have to specify table and field names (as described below) while creating a trigger. 

Each of the groups of functions described below is provided as a separately-installable extension. 

<a id="contrib-spi-autoinc"></a>

### F.43.1. autoinc — Functions for Autoincrementing Fields

`autoinc()` is a trigger that stores the next value of a sequence into an integer field. This has some overlap with the built-in "serial column" feature, but it is not the same. The trigger will replace the field's value only if that value is initially zero or null (after the action of the SQL statement that inserted or updated the row). Also, if the sequence's next value is zero, `nextval()` will be called a second time in order to obtain a non-zero value. 

To use, create a `BEFORE INSERT` (or optionally `BEFORE INSERT OR UPDATE`) trigger using this function. Specify two trigger arguments: the name of the integer column to be modified, and the name of the sequence object that will supply values. (Actually, you can specify any number of pairs of such names, if you'd like to update more than one autoincrementing column.) 

There is an example in `autoinc.example`. 

<a id="contrib-spi-insert-username"></a>

### F.43.2. insert_username — Functions for Tracking Who Changed a Table

`insert_username()` is a trigger that stores the current user's name into a text field. This can be useful for tracking who last modified a particular row within a table. 

To use, create a `BEFORE INSERT` and/or `UPDATE` trigger using this function. Specify a single trigger argument: the name of the text column to be modified. 

There is an example in `insert_username.example`. 

<a id="contrib-spi-moddatetime"></a>

### F.43.3. moddatetime — Functions for Tracking Last Modification Time

`moddatetime()` is a trigger that stores the current time into a `timestamp` field. This can be useful for tracking the last modification time of a particular row within a table. 

To use, create a `BEFORE UPDATE` trigger using this function. Specify a single trigger argument: the name of the column to be modified. The column must be of type `timestamp` or `timestamp with time zone`. 

There is an example in `moddatetime.example`.