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主要查询功能
TDengine 采用 SQL 作为查询语言。应用程序可以通过 REST API 或连接器发送 SQL 语句，用户还可以通过 TDengine 命令行工具 taos 手动执行 SQL 即席查询（Ad-Hoc Query）。TDengine 支持如下查询功能：
- 单列、多列数据查询
- 标签和数值的多种过滤条件：>, <, =, <>, like 等
- 聚合结果的分组（Group by）、排序（Order by）、约束输出（Limit/Offset）
- 数值列及聚合结果的四则运算
- 时间戳对齐的连接查询（Join Query: 隐式连接）操作
- 多种聚合/计算函数: count, max, min, avg, sum, twa, stddev, leastsquares, top, bottom, first, last, percentile, apercentile, last_row, spread, diff 等
例如：在命令行工具 taos 中，从表 d1001 中查询出 voltage > 215 的记录，按时间降序排列，仅仅输出 2 条。
taos> select * from d1001 where voltage > 215 order by ts desc limit 2;ts | current | voltage | phase |======================================================================================2018-10-03 14:38:16.800 | 12.30000 | 221 | 0.31000 |2018-10-03 14:38:15.000 | 12.60000 | 218 | 0.33000 |Query OK, 2 row(s) in set (0.001100s)
为满足物联网场景的需求，TDengine 支持几个特殊的函数，比如 twa(时间加权平均)，spread (最大值与最小值的差)，last_row(最后一条记录)等，更多与物联网场景相关的函数将添加进来。TDengine 还支持连续查询。
具体的查询语法请看 TAOS SQL 的数据查询 章节。
多表聚合查询
物联网场景中，往往同一个类型的数据采集点有多个。TDengine 采用超级表(STable)的概念来描述某一个类型的数据采集点，一张普通的表来描述一个具体的数据采集点。同时 TDengine 使用标签来描述数据采集点的静态属性，一个具体的数据采集点有具体的标签值。通过指定标签的过滤条件，TDengine 提供了一高效的方法将超级表(某一类型的数据采集点)所属的子表进行聚合查询。对普通表的聚合函数以及绝大部分操作都适用于超级表，语法完全一样。
示例一
在 TAOS Shell，查找加利福尼亚州所有智能电表采集的电压平均值，并按照 location 分组。
taos> SELECT AVG(voltage) FROM meters GROUP BY location;avg(voltage) | location |=============================================================222.000000000 | California.LosAngeles |219.200000000 | California.SanFrancisco |Query OK, 2 row(s) in set (0.002136s)
示例二
在 TAOS shell, 查找 groupId 为 2 的所有智能电表过去 24 小时的记录条数，电流的最大值。
taos> SELECT count(*), max(current) FROM meters where groupId = 2 and ts > now - 24h;cunt(*) | max(current) |==================================5 | 13.4 |Query OK, 1 row(s) in set (0.002136s)
TDengine 仅容许对属于同一个超级表的表之间进行聚合查询，不同超级表之间的聚合查询不支持。在 TAOS SQL 的数据查询 一章，查询类操作都会注明是否支持超级表。
降采样查询、插值
物联网场景里，经常需要通过降采样（down sampling）将采集的数据按时间段进行聚合。TDengine 提供了一个简便的关键词 interval 让按照时间窗口的查询操作变得极为简单。比如，将智能电表 d1001 采集的电流值每 10 秒钟求和
taos> SELECT sum(current) FROM d1001 INTERVAL(10s);ts | sum(current) |======================================================2018-10-03 14:38:00.000 | 10.300000191 |2018-10-03 14:38:10.000 | 24.900000572 |Query OK, 2 row(s) in set (0.000883s)
降采样操作也适用于超级表，比如：将加利福尼亚州所有智能电表采集的电流值每秒钟求和
taos> SELECT SUM(current) FROM meters where location like "California%" INTERVAL(1s);ts | sum(current) |======================================================2018-10-03 14:38:04.000 | 10.199999809 |2018-10-03 14:38:05.000 | 32.900000572 |2018-10-03 14:38:06.000 | 11.500000000 |2018-10-03 14:38:15.000 | 12.600000381 |2018-10-03 14:38:16.000 | 36.000000000 |Query OK, 5 row(s) in set (0.001538s)
降采样操作也支持时间偏移，比如：将所有智能电表采集的电流值每秒钟求和，但要求每个时间窗口从 500 毫秒开始
taos> SELECT SUM(current) FROM meters INTERVAL(1s, 500a);ts | sum(current) |======================================================2018-10-03 14:38:04.500 | 11.189999809 |2018-10-03 14:38:05.500 | 31.900000572 |2018-10-03 14:38:06.500 | 11.600000000 |2018-10-03 14:38:15.500 | 12.300000381 |2018-10-03 14:38:16.500 | 35.000000000 |Query OK, 5 row(s) in set (0.001521s)
物联网场景里，每个数据采集点采集数据的时间是难同步的，但很多分析算法(比如 FFT)需要把采集的数据严格按照时间等间隔的对齐，在很多系统里，需要应用自己写程序来处理，但使用 TDengine 的降采样操作就轻松解决。
如果一个时间间隔里，没有采集的数据，TDengine 还提供插值计算的功能。
语法规则细节请见 TAOS SQL 的按时间窗口切分聚合 章节。
示例代码
查询数据
在 SQL 写入 一章，我们创建了 power 数据库，并向 meters 表写入了一些数据，以下示例代码展示如何查询这个表的数据。
- Java
- Python
- Go
- Rust
- Node.js
- C#
- C
- PHP
package com.taos.example;import java.sql.*;public class RestQueryExample {private static Connection getConnection() throws SQLException {String jdbcUrl = "jdbc:TAOS-RS://localhost:6041/power?user=root&password=taosdata";return DriverManager.getConnection(jdbcUrl);}private static void printRow(ResultSet rs) throws SQLException {ResultSetMetaData meta = rs.getMetaData();for (int i = 1; i <= meta.getColumnCount(); i++) {String value = rs.getString(i);System.out.print(value);System.out.print("\t");}System.out.println();}private static void printColName(ResultSet rs) throws SQLException {ResultSetMetaData meta = rs.getMetaData();for (int i = 1; i <= meta.getColumnCount(); i++) {String colLabel = meta.getColumnLabel(i);System.out.print(colLabel);System.out.print("\t");}System.out.println();}private static void processResult(ResultSet rs) throws SQLException {printColName(rs);while (rs.next()) {printRow(rs);}}private static void queryData() throws SQLException {try (Connection conn = getConnection()) {try (Statement stmt = conn.createStatement()) {ResultSet rs = stmt.executeQuery("SELECT AVG(voltage) FROM meters GROUP BY location");processResult(rs);}}}public static void main(String[] args) throws SQLException {queryData();}}// possible output:// avg(voltage) location// 222.0 California.LosAngeles// 219.0 California.SanFrancisco
通过迭代逐行获取查询结果。
def query_api_demo(conn: taos.TaosConnection):result: taos.TaosResult = conn.query("SELECT tbname, * FROM meters LIMIT 2")print("field count:", result.field_count)print("meta of fields[1]:", result.fields[1])print("======================Iterate on result=========================")for row in result:print(row)# field count: 7# meta of fields[1]: {name: ts, type: 9, bytes: 8}# ======================Iterate on result=========================# ('d1003', datetime.datetime(2018, 10, 3, 14, 38, 5, 500000), 11.800000190734863, 221, 0.2800000011920929, 'california.losangeles', 2)# ('d1003', datetime.datetime(2018, 10, 3, 14, 38, 16, 600000), 13.399999618530273, 223, 0.28999999165534973, 'california.losangeles', 2)
一次获取所有查询结果，并把每一行转化为一个字典返回。
def fetch_all_demo(conn: taos.TaosConnection):result: taos.TaosResult = conn.query("SELECT ts, current FROM meters LIMIT 2")rows = result.fetch_all_into_dict()print("row count:", result.row_count)print("===============all data===================")print(rows)# row count: 2# ===============all data===================# [{'ts': datetime.datetime(2018, 10, 3, 14, 38, 5, 500000), 'current': 11.800000190734863},# {'ts': datetime.datetime(2018, 10, 3, 14, 38, 16, 600000), 'current': 13.399999618530273}]
package mainimport ("database/sql""fmt""time"_ "github.com/taosdata/driver-go/v2/taosRestful")func main() {var taosDSN = "root:taosdata@http(localhost:6041)/power"taos, err := sql.Open("taosRestful", taosDSN)if err != nil {fmt.Println("failed to connect TDengine, err:", err)return}defer taos.Close()rows, err := taos.Query("SELECT ts, current FROM meters LIMIT 2")if err != nil {fmt.Println("failed to select from table, err:", err)return}defer rows.Close()for rows.Next() {var r struct {ts time.Timecurrent float32}err := rows.Scan(&r.ts, &r.current)if err != nil {fmt.Println("scan error:\n", err)return}fmt.Println(r.ts, r.current)}}
use libtaos::*;fn taos_connect() -> Result<Taos, Error> {TaosCfgBuilder::default().ip("localhost").user("root").pass("taosdata").db("power").port(6030u16).build().expect("TaosCfg builder error").connect()}#[tokio::main]async fn main() -> Result<(), Error> {let taos = taos_connect().expect("connect error");let result = taos.query("SELECT ts, current FROM meters LIMIT 2").await?;// print column nameslet meta: Vec<ColumnMeta> = result.column_meta;for column in meta {print!("{}\t", column.name)}println!();// print rowslet rows: Vec<Vec<Field>> = result.rows;for row in rows {for field in row {print!("{}\t", field);}println!();}Ok(())}// output:// ts current// 2022-03-28 09:56:51.249 10.3// 2022-03-28 09:56:51.749 12.6
const taos = require("td2.0-connector");const conn = taos.connect({ host: "localhost", database: "power" });const cursor = conn.cursor();const query = cursor.query("SELECT ts, current FROM meters LIMIT 2");query.execute().then(function (result) {result.pretty();});// output:// Successfully connected to TDengine// Query OK, 2 row(s) in set (0.00317767s)// ts | current |// =======================================================// 2018-10-03 14:38:05.000 | 10.3 |// 2018-10-03 14:38:15.000 | 12.6 |
using TDengineDriver;using System.Runtime.InteropServices;namespace TDengineExample{internal class QueryExample{static void Main(){IntPtr conn = GetConnection();// run queryIntPtr res = TDengine.Query(conn, "SELECT * FROM test.meters LIMIT 2");if (TDengine.ErrorNo(res) != 0){Console.WriteLine("Failed to query since: " + TDengine.Error(res));TDengine.Close(conn);TDengine.Cleanup();return;}// get filed countint fieldCount = TDengine.FieldCount(res);Console.WriteLine("fieldCount=" + fieldCount);// print column namesList<TDengineMeta> metas = TDengine.FetchFields(res);for (int i = 0; i < metas.Count; i++){Console.Write(metas[i].name + "\t");}Console.WriteLine();// print valuesIntPtr row;while ((row = TDengine.FetchRows(res)) != IntPtr.Zero){List<TDengineMeta> metaList = TDengine.FetchFields(res);int numOfFiled = TDengine.FieldCount(res);List<String> dataRaw = new List<string>();IntPtr colLengthPrt = TDengine.FetchLengths(res);int[] colLengthArr = new int[numOfFiled];Marshal.Copy(colLengthPrt, colLengthArr, 0, numOfFiled);for (int i = 0; i < numOfFiled; i++){TDengineMeta meta = metaList[i];IntPtr data = Marshal.ReadIntPtr(row, IntPtr.Size * i);if (data == IntPtr.Zero){Console.Write("NULL\t");continue;}switch ((TDengineDataType)meta.type){case TDengineDataType.TSDB_DATA_TYPE_BOOL:bool v1 = Marshal.ReadByte(data) == 0 ? false : true;Console.Write(v1.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_TINYINT:sbyte v2 = (sbyte)Marshal.ReadByte(data);Console.Write(v2.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_SMALLINT:short v3 = Marshal.ReadInt16(data);Console.Write(v3.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_INT:int v4 = Marshal.ReadInt32(data);Console.Write(v4.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_BIGINT:long v5 = Marshal.ReadInt64(data);Console.Write(v5.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_FLOAT:float v6 = (float)Marshal.PtrToStructure(data, typeof(float));Console.Write(v6.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_DOUBLE:double v7 = (double)Marshal.PtrToStructure(data, typeof(double));Console.Write(v7.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_BINARY:string v8 = Marshal.PtrToStringUTF8(data, colLengthArr[i]);Console.Write(v8 + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_TIMESTAMP:long v9 = Marshal.ReadInt64(data);Console.Write(v9.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_NCHAR:string v10 = Marshal.PtrToStringUTF8(data, colLengthArr[i]);Console.Write(v10 + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_UTINYINT:byte v12 = Marshal.ReadByte(data);Console.Write(v12.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_USMALLINT:ushort v13 = (ushort)Marshal.ReadInt16(data);Console.Write(v13.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_UINT:uint v14 = (uint)Marshal.ReadInt32(data);Console.Write(v14.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_UBIGINT:ulong v15 = (ulong)Marshal.ReadInt64(data);Console.Write(v15.ToString() + "\t");break;case TDengineDataType.TSDB_DATA_TYPE_JSONTAG:string v16 = Marshal.PtrToStringUTF8(data, colLengthArr[i]);Console.Write(v16 + "\t");break;default:Console.Write("nonsupport data type value");break;}}Console.WriteLine();}if (TDengine.ErrorNo(res) != 0){Console.WriteLine($"Query is not complete, Error {TDengine.ErrorNo(res)} {TDengine.Error(res)}");}// exitTDengine.FreeResult(res);TDengine.Close(conn);TDengine.Cleanup();}static IntPtr GetConnection(){string host = "localhost";short port = 6030;string username = "root";string password = "taosdata";string dbname = "power";var conn = TDengine.Connect(host, username, password, dbname, port);if (conn == IntPtr.Zero){Console.WriteLine("Connect to TDengine failed");System.Environment.Exit(0);}else{Console.WriteLine("Connect to TDengine success");}return conn;}}}// output:// Connect to TDengine success// fieldCount=6// ts current voltage phase location groupid// 1648432611249 10.3 219 0.31 California.SanFrancisco 2// 1648432611749 12.6 218 0.33 California.SanFrancisco 2
// compile with:// gcc -o query_example query_example.c -ltaos#include <inttypes.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <taos.h>typedef int16_t VarDataLenT;#define TSDB_NCHAR_SIZE sizeof(int32_t)#define VARSTR_HEADER_SIZE sizeof(VarDataLenT)#define GET_FLOAT_VAL(x) (*(float *)(x))#define GET_DOUBLE_VAL(x) (*(double *)(x))#define varDataLen(v) ((VarDataLenT *)(v))[0]int printRow(char *str, TAOS_ROW row, TAOS_FIELD *fields, int numFields) {int len = 0;char split = ' ';for (int i = 0; i < numFields; ++i) {if (i > 0) {str[len++] = split;}if (row[i] == NULL) {len += sprintf(str + len, "%s", "NULL");continue;}switch (fields[i].type) {case TSDB_DATA_TYPE_TINYINT:len += sprintf(str + len, "%d", *((int8_t *)row[i]));break;case TSDB_DATA_TYPE_UTINYINT:len += sprintf(str + len, "%u", *((uint8_t *)row[i]));break;case TSDB_DATA_TYPE_SMALLINT:len += sprintf(str + len, "%d", *((int16_t *)row[i]));break;case TSDB_DATA_TYPE_USMALLINT:len += sprintf(str + len, "%u", *((uint16_t *)row[i]));break;case TSDB_DATA_TYPE_INT:len += sprintf(str + len, "%d", *((int32_t *)row[i]));break;case TSDB_DATA_TYPE_UINT:len += sprintf(str + len, "%u", *((uint32_t *)row[i]));break;case TSDB_DATA_TYPE_BIGINT:len += sprintf(str + len, "%" PRId64, *((int64_t *)row[i]));break;case TSDB_DATA_TYPE_UBIGINT:len += sprintf(str + len, "%" PRIu64, *((uint64_t *)row[i]));break;case TSDB_DATA_TYPE_FLOAT: {float fv = 0;fv = GET_FLOAT_VAL(row[i]);len += sprintf(str + len, "%f", fv);} break;case TSDB_DATA_TYPE_DOUBLE: {double dv = 0;dv = GET_DOUBLE_VAL(row[i]);len += sprintf(str + len, "%lf", dv);} break;case TSDB_DATA_TYPE_BINARY:case TSDB_DATA_TYPE_NCHAR: {int32_t charLen = varDataLen((char *)row[i] - VARSTR_HEADER_SIZE);memcpy(str + len, row[i], charLen);len += charLen;} break;case TSDB_DATA_TYPE_TIMESTAMP:len += sprintf(str + len, "%" PRId64, *((int64_t *)row[i]));break;case TSDB_DATA_TYPE_BOOL:len += sprintf(str + len, "%d", *((int8_t *)row[i]));default:break;}}return len;}/*** @brief print column name and values of each row** @param res* @return int*/static int printResult(TAOS_RES *res) {int numFields = taos_num_fields(res);TAOS_FIELD *fields = taos_fetch_fields(res);char header[256] = {0};int len = 0;for (int i = 0; i < numFields; ++i) {len += sprintf(header + len, "%s ", fields[i].name);}puts(header);TAOS_ROW row = NULL;while ((row = taos_fetch_row(res))) {char temp[256] = {0};printRow(temp, row, fields, numFields);puts(temp);}}int main() {TAOS *taos = taos_connect("localhost", "root", "taosdata", "power", 6030);if (taos == NULL) {puts("failed to connect to server");exit(EXIT_FAILURE);}TAOS_RES *res = taos_query(taos, "SELECT * FROM meters LIMIT 2");if (taos_errno(res) != 0) {printf("failed to execute taos_query. error: %s\n", taos_errstr(res));exit(EXIT_FAILURE);}printResult(res);taos_free_result(res);taos_close(taos);taos_cleanup();}// output:// ts current voltage phase location groupid// 1648432611249 10.300000 219 0.310000 California.SanFrancisco 2// 1648432611749 12.600000 218 0.330000 California.SanFrancisco 2
<?phpuse TDengine\Connection;use TDengine\Exception\TDengineException;try {// instantiate$host = 'localhost';$port = 6030;$username = 'root';$password = 'taosdata';$dbname = 'power';$connection = new Connection($host, $port, $username, $password, $dbname);// connect$connection->connect();$resource = $connection->query('SELECT ts, current FROM meters LIMIT 2');var_dump($resource->fetch());} catch (TDengineException $e) {// throw exceptionthrow $e;}
note
- 无论是使用 REST 连接还是原生连接的连接器，以上示例代码都能正常工作。
- 唯一需要注意的是：由于 REST 接口无状态， 不能使用
use db语句来切换数据库。
异步查询
除同步查询 API 之外，TDengine 还提供性能更高的异步调用 API 处理数据插入、查询操作。在软硬件环境相同的情况下，异步 API 处理数据插入的速度比同步 API 快 2-4 倍。异步 API 采用非阻塞式的调用方式，在系统真正完成某个具体数据库操作前，立即返回。调用的线程可以去处理其他工作，从而可以提升整个应用的性能。异步 API 在网络延迟严重的情况下，优点尤为突出。
需要注意的是，只有使用原生连接的连接器，才能使用异步查询功能。
- Python
- C#
- C
import timefrom ctypes import *from taos import *def fetch_callback(p_param, p_result, num_of_rows):print("fetched ", num_of_rows, "rows")p = cast(p_param, POINTER(Counter))result = TaosResult(p_result)if num_of_rows == 0:print("fetching completed")p.contents.done = Trueresult.close()returnif num_of_rows < 0:p.contents.done = Trueresult.check_error(num_of_rows)result.close()return Nonefor row in result.rows_iter(num_of_rows):print(row)p.contents.count += result.row_countresult.fetch_rows_a(fetch_callback, p_param)def query_callback(p_param, p_result, code):if p_result is None:returnresult = TaosResult(p_result)if code == 0:result.fetch_rows_a(fetch_callback, p_param)result.check_error(code)class Counter(Structure):_fields_ = [("count", c_int), ("done", c_bool)]def __str__(self):return "{ count: %d, done: %s }" % (self.count, self.done)def test_query(conn):counter = Counter(count=0)conn.query_a("select ts, current, voltage from power.meters", query_callback, byref(counter))while not counter.done:print(counter)time.sleep(1)print(counter)conn.close()if __name__ == "__main__":test_query(connect())# possible output:# { count: 0, done: False }# fetched 8 rows# 1538548685000 10.300000 219# 1538548695000 12.600000 218# 1538548696800 12.300000 221# 1538548696650 10.300000 218# 1538548685500 11.800000 221# 1538548696600 13.400000 223# 1538548685500 10.800000 223# 1538548686500 11.500000 221# fetched 0 rows# fetching completed# { count: 8, done: True }
note
这个示例程序，目前在 Windows 系统上还无法运行
using TDengineDriver;using System.Runtime.InteropServices;namespace TDengineExample{public class AsyncQueryExample{static void Main(){IntPtr conn = GetConnection();QueryAsyncCallback queryAsyncCallback = new QueryAsyncCallback(QueryCallback);TDengine.QueryAsync(conn, "select * from meters", queryAsyncCallback, IntPtr.Zero);Thread.Sleep(2000);TDengine.Close(conn);TDengine.Cleanup();}static void QueryCallback(IntPtr param, IntPtr taosRes, int code){if (code == 0 && taosRes != IntPtr.Zero){FetchRowAsyncCallback fetchRowAsyncCallback = new FetchRowAsyncCallback(FetchRowCallback);TDengine.FetchRowAsync(taosRes, fetchRowAsyncCallback, param);}else{Console.WriteLine($"async query data failed, failed code {code}");}}static void FetchRowCallback(IntPtr param, IntPtr taosRes, int numOfRows){if (numOfRows > 0){Console.WriteLine($"{numOfRows} rows async retrieved");DisplayRes(taosRes);TDengine.FetchRowAsync(taosRes, FetchRowCallback, param);}else{if (numOfRows == 0){Console.WriteLine("async retrieve complete.");}else{Console.WriteLine($"FetchRowAsync callback error, error code {numOfRows}");}TDengine.FreeResult(taosRes);}}public static void DisplayRes(IntPtr res){if (!IsValidResult(res)){TDengine.Cleanup();System.Environment.Exit(1);}List<TDengineMeta> metaList = TDengine.FetchFields(res);int fieldCount = metaList.Count;// metaList.ForEach((item) => { Console.Write("{0} ({1}) \t|\t", item.name, item.size); });List<object> dataList = QueryRes(res, metaList);for (int index = 0; index < dataList.Count; index++){if (index % fieldCount == 0 && index != 0){Console.WriteLine("");}Console.Write("{0} \t|\t", dataList[index].ToString());}Console.WriteLine("");}public static bool IsValidResult(IntPtr res){if ((res == IntPtr.Zero) || (TDengine.ErrorNo(res) != 0)){if (res != IntPtr.Zero){Console.Write("reason: " + TDengine.Error(res));return false;}Console.WriteLine("");return false;}return true;}private static List<object> QueryRes(IntPtr res, List<TDengineMeta> meta){IntPtr taosRow;List<object> dataRaw = new();while ((taosRow = TDengine.FetchRows(res)) != IntPtr.Zero){dataRaw.AddRange(FetchRow(taosRow, res));}if (TDengine.ErrorNo(res) != 0){Console.Write("Query is not complete, Error {0} {1}", TDengine.ErrorNo(res), TDengine.Error(res));}TDengine.FreeResult(res);Console.WriteLine("");return dataRaw;}public static List<object> FetchRow(IntPtr taosRow, IntPtr taosRes)//, List<TDengineMeta> metaList, int numOfFiled{List<TDengineMeta> metaList = TDengine.FetchFields(taosRes);int numOfFiled = TDengine.FieldCount(taosRes);List<object> dataRaw = new();IntPtr colLengthPrt = TDengine.FetchLengths(taosRes);int[] colLengthArr = new int[numOfFiled];Marshal.Copy(colLengthPrt, colLengthArr, 0, numOfFiled);for (int i = 0; i < numOfFiled; i++){TDengineMeta meta = metaList[i];IntPtr data = Marshal.ReadIntPtr(taosRow, IntPtr.Size * i);if (data == IntPtr.Zero){dataRaw.Add("NULL");continue;}switch ((TDengineDataType)meta.type){case TDengineDataType.TSDB_DATA_TYPE_BOOL:bool v1 = Marshal.ReadByte(data) != 0;dataRaw.Add(v1);break;case TDengineDataType.TSDB_DATA_TYPE_TINYINT:sbyte v2 = (sbyte)Marshal.ReadByte(data);dataRaw.Add(v2);break;case TDengineDataType.TSDB_DATA_TYPE_SMALLINT:short v3 = Marshal.ReadInt16(data);dataRaw.Add(v3);break;case TDengineDataType.TSDB_DATA_TYPE_INT:int v4 = Marshal.ReadInt32(data);dataRaw.Add(v4);break;case TDengineDataType.TSDB_DATA_TYPE_BIGINT:long v5 = Marshal.ReadInt64(data);dataRaw.Add(v5);break;case TDengineDataType.TSDB_DATA_TYPE_FLOAT:float v6 = (float)Marshal.PtrToStructure(data, typeof(float));dataRaw.Add(v6);break;case TDengineDataType.TSDB_DATA_TYPE_DOUBLE:double v7 = (double)Marshal.PtrToStructure(data, typeof(double));dataRaw.Add(v7);break;case TDengineDataType.TSDB_DATA_TYPE_BINARY:string v8 = Marshal.PtrToStringUTF8(data, colLengthArr[i]);dataRaw.Add(v8);break;case TDengineDataType.TSDB_DATA_TYPE_TIMESTAMP:long v9 = Marshal.ReadInt64(data);dataRaw.Add(v9);break;case TDengineDataType.TSDB_DATA_TYPE_NCHAR:string v10 = Marshal.PtrToStringUTF8(data, colLengthArr[i]);dataRaw.Add(v10);break;case TDengineDataType.TSDB_DATA_TYPE_UTINYINT:byte v12 = Marshal.ReadByte(data);dataRaw.Add(v12.ToString());break;case TDengineDataType.TSDB_DATA_TYPE_USMALLINT:ushort v13 = (ushort)Marshal.ReadInt16(data);dataRaw.Add(v13);break;case TDengineDataType.TSDB_DATA_TYPE_UINT:uint v14 = (uint)Marshal.ReadInt32(data);dataRaw.Add(v14);break;case TDengineDataType.TSDB_DATA_TYPE_UBIGINT:ulong v15 = (ulong)Marshal.ReadInt64(data);dataRaw.Add(v15);break;case TDengineDataType.TSDB_DATA_TYPE_JSONTAG:string v16 = Marshal.PtrToStringUTF8(data, colLengthArr[i]);dataRaw.Add(v16);break;default:dataRaw.Add("nonsupport data type");break;}}return dataRaw;}static IntPtr GetConnection(){string host = "localhost";short port = 6030;string username = "root";string password = "taosdata";string dbname = "power";var conn = TDengine.Connect(host, username, password, dbname, port);if (conn == IntPtr.Zero){Console.WriteLine("Connect to TDengine failed");Environment.Exit(0);}else{Console.WriteLine("Connect to TDengine success");}return conn;}}}//output:// Connect to TDengine success// 8 rows async retrieved// 1538548685500 | 11.8 | 221 | 0.28 | california.losangeles | 2 |// 1538548696600 | 13.4 | 223 | 0.29 | california.losangeles | 2 |// 1538548685000 | 10.8 | 223 | 0.29 | california.losangeles | 3 |// 1538548686500 | 11.5 | 221 | 0.35 | california.losangeles | 3 |// 1538548685000 | 10.3 | 219 | 0.31 | california.sanfrancisco | 2 |// 1538548695000 | 12.6 | 218 | 0.33 | california.sanfrancisco | 2 |// 1538548696800 | 12.3 | 221 | 0.31 | california.sanfrancisco | 2 |// 1538548696650 | 10.3 | 218 | 0.25 | california.sanfrancisco | 3 |// async retrieve complete.
/*** @brief call back function of taos_fetch_row_a** @param param : the third parameter you passed to taos_fetch_row_a* @param res : pointer of TAOS_RES* @param numOfRow : number of rows fetched in this batch. will be 0 if there is no more data.* @return void**/void *fetch_row_callback(void *param, TAOS_RES *res, int numOfRow) {printf("numOfRow = %d \n", numOfRow);int numFields = taos_num_fields(res);TAOS_FIELD *fields = taos_fetch_fields(res);TAOS *_taos = (TAOS *)param;if (numOfRow > 0) {for (int i = 0; i < numOfRow; ++i) {TAOS_ROW row = taos_fetch_row(res);char temp[256] = {0};printRow(temp, row, fields, numFields);puts(temp);}taos_fetch_rows_a(res, fetch_row_callback, _taos);} else {printf("no more data, close the connection.\n");taos_free_result(res);taos_close(_taos);taos_cleanup();}}/*** @brief callback function of taos_query_a** @param param: the fourth parameter you passed to taos_query_a* @param res : the result set* @param code : status code* @return void**/void *select_callback(void *param, TAOS_RES *res, int code) {printf("query callback ...\n");TAOS *_taos = (TAOS *)param;if (code == 0 && res) {printHeader(res);taos_fetch_rows_a(res, fetch_row_callback, _taos);} else {printf("failed to execute taos_query. error: %s\n", taos_errstr(res));taos_free_result(res);taos_close(_taos);taos_cleanup();exit(EXIT_FAILURE);}}int main() {TAOS *taos = taos_connect("localhost", "root", "taosdata", "power", 6030);if (taos == NULL) {puts("failed to connect to server");exit(EXIT_FAILURE);}// param one is the connection returned by taos_connect.// param two is the SQL to execute.// param three is the callback function.// param four can be any pointer. It will be passed to your callback function as the first parameter. we use taos// here, because we want to close it after getting data.taos_query_a(taos, "SELECT * FROM meters", select_callback, taos);sleep(1);}// output:// query callback ...// ts current voltage phase location groupid// numOfRow = 8// 1538548685500 11.800000 221 0.280000 california.losangeles 2// 1538548696600 13.400000 223 0.290000 california.losangeles 2// 1538548685000 10.800000 223 0.290000 california.losangeles 3// 1538548686500 11.500000 221 0.350000 california.losangeles 3// 1538548685000 10.300000 219 0.310000 california.sanfrancisco 2// 1538548695000 12.600000 218 0.330000 california.sanfrancisco 2// 1538548696800 12.300000 221 0.310000 california.sanfrancisco 2// 1538548696650 10.300000 218 0.250000 california.sanfrancisco 3// numOfRow = 0// no more data, close the connection.
