436 lines
17 KiB
HTML
436 lines
17 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Example: Weather table function" />
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<meta name="abstract" content="This is an example table function that returns weather information for various cities in the United States." />
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<meta name="description" content="This is an example table function that returns weather information for various cities in the United States." />
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<meta name="DC.subject" content="examples, weather table UDF, CREATE FUNCTION statement" />
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<meta name="keywords" content="examples, weather table UDF, CREATE FUNCTION statement" />
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<meta name="DC.Relation" scheme="URI" content="rbafyuwexam.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rbafyudfweather" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Example: Weather table function</title>
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</head>
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<body id="rbafyudfweather"><a name="rbafyudfweather"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Example: Weather table function</h1>
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<div><p>This is an example table function that returns weather information
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for various cities in the United States. </p>
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<div class="section"> <div class="note"><span class="notetitle">Note:</span> By using the code examples, you agree to the terms of the <a href="codedisclaimer.htm">Code license and disclaimer information</a>.</div>
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</div>
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<div class="section"><p>The weather date for these cities is read in from an external
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file, as indicated in the comments contained in the example program. The data
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includes the name of a city followed by its weather information. This pattern
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is repeated for the other cities.</p>
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<pre>#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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#include <sqludf.h> /* for use in compiling User Defined Function */
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#define SQL_NOTNULL 0 /* Nulls Allowed - Value is not Null */
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#define SQL_ISNULL -1 /* Nulls Allowed - Value is Null */
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#define SQL_TYP_VARCHAR 448
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#define SQL_TYP_INTEGER 496
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#define SQL_TYP_FLOAT 480
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/* Short and long city name structure */
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typedef struct {
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char * city_short ;
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char * city_long ;
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} city_area ;
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/* Scratchpad data */ <strong><em>(See note 1)</em></strong>
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/* Preserve information from one function call to the next call */
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typedef struct {
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/* FILE * file_ptr; if you use weather data text file */
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int file_pos ; /* if you use a weather data buffer */
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} scratch_area ;
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/* Field descriptor structure */
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typedef struct {
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char fld_field[31] ; /* Field data */
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int fld_ind ; /* Field null indicator data */
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int fld_type ; /* Field type */
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int fld_length ; /* Field length in the weather data */
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int fld_offset ; /* Field offset in the weather data */
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} fld_desc ;
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/* Short and long city name data */
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city_area cities[] = {
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{ "alb", "Albany, NY" },
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{ "atl", "Atlanta, GA" },
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.
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.
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.
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{ "wbc", "Washington DC, DC" },
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/* You may want to add more cities here */
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/* Do not forget a null termination */
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{ ( char * ) 0, ( char * ) 0 }
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} ;
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/* Field descriptor data */
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fld_desc fields[] = {
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{ "", SQL_ISNULL, SQL_TYP_VARCHAR, 30, 0 }, /* city */
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{ "", SQL_ISNULL, SQL_TYP_INTEGER, 3, 2 }, /* temp_in_f */
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{ "", SQL_ISNULL, SQL_TYP_INTEGER, 3, 7 }, /* humidity */
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{ "", SQL_ISNULL, SQL_TYP_VARCHAR, 5, 13 }, /* wind */
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{ "", SQL_ISNULL, SQL_TYP_INTEGER, 3, 19 }, /* wind_velocity */
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{ "", SQL_ISNULL, SQL_TYP_FLOAT, 5, 24 }, /* barometer */
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{ "", SQL_ISNULL, SQL_TYP_VARCHAR, 25, 30 }, /* forecast */
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/* You may want to add more fields here */
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/* Do not forget a null termination */
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{ ( char ) 0, 0, 0, 0, 0 }
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} ;
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/* Following is the weather data buffer for this example. You */
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/* may want to keep the weather data in a separate text file. */
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/* Uncomment the following fopen() statement. Note that you */
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/* need to specify the full path name for this file. */
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char * weather_data[] = {
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"alb.forecast",
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" 34 28% wnw 3 30.53 clear",
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"atl.forecast",
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" 46 89% east 11 30.03 fog",
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.
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.
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.
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"wbc.forecast",
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" 38 96% ene 16 30.31 light rain",
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/* You may want to add more weather data here */
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/* Do not forget a null termination */
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( char * ) 0
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} ;
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#ifdef __cplusplus
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extern "C"
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#endif
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/* This is a subroutine. */
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/* Find a full city name using a short name */
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int get_name( char * short_name, char * long_name ) {
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int name_pos = 0 ;
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while ( cities[name_pos].city_short != ( char * ) 0 ) {
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if (strcmp(short_name, cities[name_pos].city_short) == 0) {
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strcpy( long_name, cities[name_pos].city_long ) ;
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/* A full city name found */
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return( 0 ) ;
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}
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name_pos++ ;
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}
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/* can not find such city in the city data */
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strcpy( long_name, "Unknown City" ) ;
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return( -1 ) ;
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}
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#ifdef __cplusplus
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extern "C"
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#endif
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/* This is a subroutine. */
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/* Clean all field data and field null indicator data */
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int clean_fields( int field_pos ) {
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while (fields[field_pos].fld_length !=0 ) {
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memset( fields[field_pos].fld_field, '\0', 31 ) ;
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fields[field_pos].fld_ind = SQL_ISNULL ;
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field_pos++ ;
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}
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return( 0 ) ;
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}
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#ifdef __cplusplus
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extern "C"
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#endif
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/* This is a subroutine. */
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/* Fills all field data and field null indicator data ... */
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/* ... from text weather data */
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int get_value( char * value, int field_pos ) {
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fld_desc * field ;
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char field_buf[31] ;
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double * double_ptr ;
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int * int_ptr, buf_pos ;
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while ( fields[field_pos].fld_length != 0 ) {
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field = &fields[field_pos] ;
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memset( field_buf, '\0', 31 ) ;
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memcpy( field_buf,
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( value + field->fld_offset ),
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field->fld_length ) ;
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buf_pos = field->fld_length ;
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while ( ( buf_pos > 0 ) &&
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( field_buf[buf_pos] == ' ' ) )
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field_buf[buf_pos--] = '\0' ;
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buf_pos = 0 ;
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while ( ( buf_pos < field->fld_length ) &&
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( field_buf[buf_pos] == ' ' ) )
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buf_pos++ ;
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if ( strlen( ( char * ) ( field_buf + buf_pos ) ) > 0 ||
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strcmp( ( char * ) ( field_buf + buf_pos ), "n/a") != 0 ) {
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field->fld_ind = SQL_NOTNULL ;
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/* Text to SQL type conversion */
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switch( field->fld_type ) {
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case SQL_TYP_VARCHAR:
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strcpy( field->fld_field,
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( char * ) ( field_buf + buf_pos ) ) ;
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break ;
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case SQL_TYP_INTEGER:
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int_ptr = ( int * ) field->fld_field ;
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*int_ptr = atoi( ( char * ) ( field_buf + buf_pos ) ) ;
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break ;
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case SQL_TYP_FLOAT:
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double_ptr = ( double * ) field->fld_field ;
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*double_ptr = atof( ( char * ) ( field_buf + buf_pos ) ) ;
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break ;
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/* You may want to add more text to SQL type conversion here */
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}
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}
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field_pos++ ;
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}
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return( 0 ) ;
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}
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#ifdef __cplusplus
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extern "C"
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#endif
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void SQL_API_FN weather( /* Return row fields */
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SQLUDF_VARCHAR * city,
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SQLUDF_INTEGER * temp_in_f,
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SQLUDF_INTEGER * humidity,
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SQLUDF_VARCHAR * wind,
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SQLUDF_INTEGER * wind_velocity,
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SQLUDF_DOUBLE * barometer,
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SQLUDF_VARCHAR * forecast,
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/* You may want to add more fields here */
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/* Return row field null indicators */
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SQLUDF_NULLIND * city_ind,
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SQLUDF_NULLIND * temp_in_f_ind,
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SQLUDF_NULLIND * humidity_ind,
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SQLUDF_NULLIND * wind_ind,
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SQLUDF_NULLIND * wind_velocity_ind,
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SQLUDF_NULLIND * barometer_ind,
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SQLUDF_NULLIND * forecast_ind,
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/* You may want to add more field indicators here */
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/* UDF always-present (trailing) input arguments */
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SQLUDF_TRAIL_ARGS_ALL
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) {
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scratch_area * save_area ;
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char line_buf[81] ;
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int line_buf_pos ;
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/* SQLUDF_SCRAT is part of SQLUDF_TRAIL_ARGS_ALL */
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/* Preserve information from one function call to the next call */
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save_area = ( scratch_area * ) ( SQLUDF_SCRAT->data ) ;
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/* SQLUDF_CALLT is part of SQLUDF_TRAIL_ARGS_ALL */
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switch( SQLUDF_CALLT ) {
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/* First call UDF: Open table and fetch first row */
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case SQL_TF_OPEN:
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/* If you use a weather data text file specify full path */
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/* save_area->file_ptr = fopen("tblsrv.dat","r"); */
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save_area->file_pos = 0 ;
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break ;
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/* Normal call UDF: Fetch next row */ <strong><em>(See note 2)</em></strong>
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case SQL_TF_FETCH:
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/* If you use a weather data text file */
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/* memset(line_buf, '\0', 81); */
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/* if (fgets(line_buf, 80, save_area->file_ptr) == NULL) { */
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if ( weather_data[save_area->file_pos] == ( char * ) 0 ) {
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/* SQLUDF_STATE is part of SQLUDF_TRAIL_ARGS_ALL */
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strcpy( SQLUDF_STATE, "02000" ) ;
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break ;
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}
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memset( line_buf, '\0', 81 ) ;
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strcpy( line_buf, weather_data[save_area->file_pos] ) ;
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line_buf[3] = '\0' ;
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/* Clean all field data and field null indicator data */
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clean_fields( 0 ) ;
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/* Fills city field null indicator data */
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fields[0].fld_ind = SQL_NOTNULL ;
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/* Find a full city name using a short name */
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/* Fills city field data */
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if ( get_name( line_buf, fields[0].fld_field ) == 0 ) {
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save_area->file_pos++ ;
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/* If you use a weather data text file */
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/* memset(line_buf, '\0', 81); */
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/* if (fgets(line_buf, 80, save_area->file_ptr) == NULL) { */
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if ( weather_data[save_area->file_pos] == ( char * ) 0 ) {
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/* SQLUDF_STATE is part of SQLUDF_TRAIL_ARGS_ALL */
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strcpy( SQLUDF_STATE, "02000" ) ;
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break ;
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}
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memset( line_buf, '\0', 81 ) ;
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strcpy( line_buf, weather_data[save_area->file_pos] ) ;
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line_buf_pos = strlen( line_buf ) ;
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while ( line_buf_pos > 0 ) {
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if ( line_buf[line_buf_pos] >= ' ' )
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line_buf_pos = 0 ;
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else {
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line_buf[line_buf_pos] = '\0' ;
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line_buf_pos-- ;
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}
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}
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}
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/* Fills field data and field null indicator data ... */
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/* ... for selected city from text weather data */
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get_value( line_buf, 1 ) ; /* Skips city field */
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/* Builds return row fields */
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strcpy( city, fields[0].fld_field ) ;
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memcpy( (void *) temp_in_f,
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fields[1].fld_field,
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sizeof( SQLUDF_INTEGER ) ) ;
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memcpy( (void *) humidity,
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fields[2].fld_field,
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sizeof( SQLUDF_INTEGER ) ) ;
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strcpy( wind, fields[3].fld_field ) ;
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memcpy( (void *) wind_velocity,
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fields[4].fld_field,
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sizeof( SQLUDF_INTEGER ) ) ;
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memcpy( (void *) barometer,
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fields[5].fld_field,
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sizeof( SQLUDF_DOUBLE ) ) ;
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strcpy( forecast, fields[6].fld_field ) ;
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/* Builds return row field null indicators */
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memcpy( (void *) city_ind,
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&(fields[0].fld_ind),
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sizeof( SQLUDF_NULLIND ) ) ;
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memcpy( (void *) temp_in_f_ind,
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&(fields[1].fld_ind),
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sizeof( SQLUDF_NULLIND ) ) ;
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memcpy( (void *) humidity_ind,
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&(fields[2].fld_ind),
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sizeof( SQLUDF_NULLIND ) ) ;
|
||
|
|
memcpy( (void *) wind_ind,
|
||
|
|
&(fields[3].fld_ind),
|
||
|
|
sizeof( SQLUDF_NULLIND ) ) ;
|
||
|
|
memcpy( (void *) wind_velocity_ind,
|
||
|
|
&(fields[4].fld_ind),
|
||
|
|
sizeof( SQLUDF_NULLIND ) ) ;
|
||
|
|
memcpy( (void *) barometer_ind,
|
||
|
|
&(fields[5].fld_ind),
|
||
|
|
sizeof( SQLUDF_NULLIND ) ) ;
|
||
|
|
memcpy( (void *) forecast_ind,
|
||
|
|
&(fields[6].fld_ind),
|
||
|
|
sizeof( SQLUDF_NULLIND ) ) ;
|
||
|
|
|
||
|
|
/* Next city weather data */
|
||
|
|
save_area->file_pos++ ;
|
||
|
|
|
||
|
|
break ;
|
||
|
|
|
||
|
|
/* Special last call UDF for clean up (no real args!): Close table */ <strong><em>(See note 3)</em></strong>
|
||
|
|
case SQL_TF_CLOSE:
|
||
|
|
/* If you use a weather data text file */
|
||
|
|
/* fclose(save_area->file_ptr); */
|
||
|
|
/* save_area->file_ptr = NULL; */
|
||
|
|
save_area->file_pos = 0 ;
|
||
|
|
break ;
|
||
|
|
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
</pre>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Referring to the embedded numbers in this UDF code, observe that:</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"> <ol><li>The scratchpad is defined. The <samp class="codeph">row</samp> variable is initialized
|
||
|
|
on the OPEN call, and the <samp class="codeph">iptr</samp> array and <samp class="codeph">nbr_rows</samp> variable
|
||
|
|
are filled in by the <em>mystery</em> function at open time.</li>
|
||
|
|
<li>FETCH traverses the <samp class="codeph">iptr</samp> array, using row as an index,
|
||
|
|
and moves the values of interest from the current element of <samp class="codeph">iptr</samp> to
|
||
|
|
the location pointed to by <samp class="codeph">out_c1, out_c2</samp>, and <samp class="codeph">out_c3</samp> result
|
||
|
|
value pointers.</li>
|
||
|
|
<li>Finally, CLOSE frees the storage acquired by OPEN and anchored in the
|
||
|
|
scratchpad.</li>
|
||
|
|
</ol>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Following is the CREATE FUNCTION statement for this UDF:</p>
|
||
|
|
<pre> <strong>CREATE FUNCTION</strong> tfweather_u()
|
||
|
|
<strong>RETURNS TABLE</strong> (CITY <strong>VARCHAR</strong>(25),
|
||
|
|
TEMP_IN_F <strong>INTEGER</strong>,
|
||
|
|
HUMIDITY <strong>INTEGER</strong>,
|
||
|
|
WIND <strong>VARCHAR</strong>(5),
|
||
|
|
WIND_VELOCITY <strong>INTEGER</strong>,
|
||
|
|
BAROMETER <strong>FLOAT</strong>,
|
||
|
|
FORECAST <strong>VARCHAR</strong>(25))
|
||
|
|
<strong>SPECIFIC</strong> tfweather_u
|
||
|
|
<strong> DISALLOW PARALLEL
|
||
|
|
NOT FENCED
|
||
|
|
DETERMINISTIC
|
||
|
|
NO SQL
|
||
|
|
NO EXTERNAL ACTION
|
||
|
|
SCRATCHPAD
|
||
|
|
NO FINAL CALL
|
||
|
|
LANGUAGE C
|
||
|
|
PARAMETER STYLE DB2SQL
|
||
|
|
EXTERNAL NAME</strong> 'LIB1/WEATHER(weather)';</pre>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>Referring to the embedded numbered notes, observe
|
||
|
|
that:</p>
|
||
|
|
<ul><li>It does not take any input, and returns 7 output columns.</li>
|
||
|
|
<li>SCRATCHPAD is specified, so DB2<sup>®</sup> allocates, properly initializes and
|
||
|
|
passes the scratchpad argument.</li>
|
||
|
|
<li>NO FINAL CALL is specified.</li>
|
||
|
|
<li>The function is specified as NOT DETERMINISTIC, because it depends on
|
||
|
|
more than the SQL input arguments. That is, it depends on the mystery function
|
||
|
|
and we assume that the content can vary from execution to execution.</li>
|
||
|
|
<li>DISALLOW PARALLEL is required for table functions.</li>
|
||
|
|
<li>CARDINALITY 100 is an estimate of the expected number of rows returned,
|
||
|
|
provided to the DB2 optimizer.</li>
|
||
|
|
<li>DBINFO is not used, and the optimization to only return the columns needed
|
||
|
|
by the particular statement referencing the function is not implemented.</li>
|
||
|
|
<li>NOT NULL CALL is specified, so the UDF will not be called if any of its
|
||
|
|
input SQL arguments are NULL, and does not need to check for this condition.</li>
|
||
|
|
</ul>
|
||
|
|
</div>
|
||
|
|
<div class="section"><p>To select all of the rows generated by this table function, use
|
||
|
|
the following query:</p>
|
||
|
|
<pre><strong>SELECT</strong> *
|
||
|
|
<strong>FROM TABLE</strong> (tfweather_u())x</pre>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafyuwexam.htm" title="These examples show how to implement UDF code by using SQL functions and external functions.">Examples: UDF code</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|