flink keyBy process里面如果条件查询tidb表的数据的话该怎么合理的实现

在Flink中使用KeyBy操作并不会改变数据的分区方式，只是将相同的键值（Key）的数据分到同一个TaskManager中处理。如果您需要在KeyBy之后进行条件查询TiDB表的数据，可以使用Flink的`RichFlatMapFunction`或`RichMapFunction`，在函数的`open`方法中初始化TiDB连接，并在`flatMap`或`map`方法中执行查询操作。

以下是一个示例代码，演示了如何使用`RichFlatMapFunction`和TiDB连接器从TiDB表中查询数据：

import org.apache.flink.api.common.functions.RichFlatMapFunction;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.table.api.bridge.java.StreamTableEnvironment;
import org.apache.flink.table.api.EnvironmentSettings;
import org.apache.flink.table.api.TableResult;
import org.apache.flink.connector.jdbc.JdbcConnectionOptions;
import org.apache.flink.connector.jdbc.JdbcSink;
import org.apache.flink.connector.jdbc.JdbcStatementBuilder;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.table.api.Table;
import org.apache.flink.types.Row;
import org.apache.flink.shaded.guava18.com.google.common.collect.ImmutableList;

import java.sql.*;
import java.util.Properties;

public class QueryTiDBDataWithKeyBy {

    public static void main(String[] args) {

        // set up the execution environment
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        StreamTableEnvironment tableEnv = StreamTableEnvironment.create(
            env,
            EnvironmentSettings.newInstance().useBlinkPlanner().inStreamingMode().build()
        );

        // configure TiDB properties
        Properties properties = new Properties();
        properties.setProperty("database-url", "jdbc:mysql://<tidb_ip>:<tidb_port>/<database_name>");
        properties.setProperty("username", "<tidb_username>");
        properties.setProperty("password", "<tidb_password>");
        properties.setProperty("driver", "com.mysql.jdbc.Driver");

        // register TiDB table
        tableEnv.executeSql(
            "CREATE TABLE my_table (\n" +
            "    id BIGINT,\n" +
            "    name STRING,\n" +
            "    age INT\n" +
            ") WITH (\n" +
            "    'connector' = 'jdbc',\n" +
            "    'properties' = '" + properties.toString() + "',\n" +
            "    'table-name' = 'my_table'\n" +
            ")"
        );

        // KeyBy operation
        DataStream<Row> stream = tableEnv.toDataStream(tableEnv.from("my_table"))
            .keyBy(row -> row.getField("age"));

        // flatMap with TiDB query
        DataStream<Row> result = stream.flatMap(new RichFlatMapFunction<Row, Row>() {

            private Connection connection;
            private PreparedStatement statement;

            @Override
            public void open(Configuration parameters) throws Exception {
                super.open(parameters);
                connection = DriverManager.getConnection("jdbc:mysql://<tidb_ip>:<tidb_port>/<database_name>", "<tidb_username>", "<tidb_password>");
                statement = connection.prepareStatement("SELECT * FROM my_table WHERE age > ?");
            }

            @Override
            public void flatMap(Row row, Collector<Row> collector) throws Exception {
                statement.setInt(1, (int) row.getField(0));
                ResultSet resultSet = statement.executeQuery();
                while (resultSet.next()) {
                    collector.collect(Row.of(resultSet.getLong(1), resultSet.getString(2), resultSet.getInt(3)));
                }
            }

            @Override
            public void close() throws Exception {
                super.close();
                statement.close();
                connection.close();
            }
        });

        // print the result to console
        result.print();

        try {
            env.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

在上面的示例中，我们首先设置了TiDB连接属性，并在Flink中注册了TiDB表。然后，我们使用`keyBy`操作将数据按照年龄分组，并在`flatMap`方法中使用TiDB连接器从表中查询数据。最后，我们将结果打印到控制台。

请注意，在上面的示例中，我们使用了`RichFlatMapFunction`，这是因为在`open`方法中需要初始化TiDB连接，而在`flatMap`方法中需要执行查询操作。如果您使用`FlatMapFunction`，则无法在`open`方法中初始化TiDB连接。