homework-jianmu/docs/examples/c-ws/query_data_demo.c

71 lines
2.2 KiB
C

/*
* Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
*
* This program is free software: you can use, redistribute, and/or modify
* it under the terms of the GNU Affero General Public License, version 3
* or later ("AGPL"), as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
// TAOS standard API example. The same syntax as MySQL, but only a subset
// to compile: gcc -o query_data_demo query_data_demo.c -ltaos
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "taosws.h"
static int DemoQueryData() {
// ANCHOR: query_data
int code = 0;
char *dsn = "ws://localhost:6041";
// connect
WS_TAOS *taos = ws_connect(dsn);
if (taos == NULL) {
fprintf(stderr, "Failed to connect to %s, ErrCode: 0x%x, ErrMessage: %s.\n", dsn, ws_errno(NULL), ws_errstr(NULL));
return -1;
}
// query data, please make sure the database and table are already created
const char *sql = "SELECT ts, current, location FROM power.meters limit 100";
WS_RES *result = ws_query(taos, sql);
code = ws_errno(result);
if (code != 0) {
fprintf(stderr, "Failed to query data from power.meters, sql: %s, ErrCode: 0x%x, ErrMessage: %s\n.", sql, code,
ws_errstr(result));
ws_close(taos);
return -1;
}
WS_ROW row = NULL;
int rows = 0;
int num_fields = ws_field_count(result);
const WS_FIELD *fields = ws_fetch_fields(result);
fprintf(stdout, "query successfully, got %d fields, the sql is: %s.\n", num_fields, sql);
// fetch the records row by row
while ((row = ws_fetch_row(result))) {
// Add your data processing logic here
rows++;
}
fprintf(stdout, "total rows: %d\n", rows);
ws_free_result(result);
// close & clean
ws_close(taos);
return 0;
// ANCHOR_END: query_data
}
int main(int argc, char *argv[]) { return DemoQueryData(); }