ApsaraDB for ClickHouse:Import data from ApsaraDB RDS for MySQL or PolarDB for MySQL

Prerequisites

• A destination ApsaraDB for ClickHouse cluster is created. The destination ApsaraDB for ClickHouse cluster and the data source reside in the same region and use the same virtual private cloud (VPC). For more information, see Create an ApsaraDB for ClickHouse cluster.

• A privileged database account is created for the destination ApsaraDB for ClickHouse cluster. For more information, see Create an account.

• The IP address of the ApsaraDB for ClickHouse cluster is added to the whitelist of the ApsaraDB RDS for MySQL instance. For more information, see Configure an IP address whitelist.

  Note

  You can execute the SELECT * FROM system.clusters; statement to query the IP address of the ApsaraDB for ClickHouse cluster.

Step 1: Create a table in the ApsaraDB RDS for MySQL instance and write data to the table

1. Connect to the ApsaraDB RDS for MySQL instance by using Data Management (DMS). For more information, see Use DMS to log on to an ApsaraDB RDS for MySQL instance.

2. Execute the CREATE DATABASE statement to create a database named testdb.

   CREATE DATABASE testdb;

3. Execute the CREATE TABLE statement to create the mysql_test_table table in the testdb database.

   CREATE TABLE testdb.mysql_test_table (
     v1 Int NOT NULL,
     v2 Int DEFAULT NULL,
     v3 Float DEFAULT NULL
   ) ENGINE=InnoDB;

4. Write data to the mysql_test_table table.

   INSERT INTO testdb.mysql_test_table VALUES (4,4,4.0),(1,1,2.0),(1,1,0.0),(4,1,2.0),(7,1,3.0);

Step 2: Create a table in ApsaraDB for ClickHouse

1. Connect to the ApsaraDB for ClickHouse cluster by using DMS. For more information, see Use DMS to connect to an ApsaraDB for ClickHouse cluster.

2. Execute the CREATE TABLE statement to create a table. In the following example, the clickhouse_test_table table is created in the default database.

   CREATE TABLE default.clickhouse_test_table ON CLUSTER default (
   v1 Int32, 
   v2 Nullable(Int32),
   v3 Nullable(Float32)
   ) ENGINE = MergeTree ORDER BY v1;

   Note

   • The data types of a table in ApsaraDB for ClickHouse must be mapped to the data types of a table in ApsaraDB RDS for MySQL. For more information about the mappings, see the Data type mappings section in this topic.

   • If NOT NULL is not specified for a column in the statement that you use to create a table in the ApsaraDB RDS for MySQL instance, the value of the column can be NULL. The corresponding column in the statement that you use to create a table in ApsaraDB for ClickHouse is identified as Nullable.

3. (Optional) Create a distributed table named clickhouse_test_table_distributed.

   Note

   If your ApsaraDB for ClickHouse cluster is a multi-node cluster, we recommend that you create a distributed table. Distributed tables use the storage and computing resources of each server in the ApsaraDB for ClickHouse cluster to achieve the efficient execution of data write and query operations. Distributed tables not only support excellent horizontal scalability but also ensure high performance and high availability.

   CREATE TABLE clickhouse_test_table_distributed ON CLUSTER default
    AS clickhouse_test_table
   ENGINE = Distributed(default, default, clickhouse_test_table, rand());

Step 3: Read data from the ApsaraDB RDS for MySQL instance and write data to the ApsaraDB for ClickHouse cluster

Connect to the ApsaraDB for ClickHouse cluster by using DMS and execute the migration statement. For more information, see Use DMS to connect to an ApsaraDB for ClickHouse cluster.

Syntax:

INSERT INTO <Name of the table in ApsaraDB for ClickHouse> select * from mysql('<Endpoint of the ApsaraDB RDS for MySQL instance>:<Port>', '<ApsaraDB RDS for MySQL database name>','<Name of the table in the ApsaraDB RDS for MySQL instance>', '<Database account of ApsaraDB RDS for MySQL>', '<Password of the database account of ApsaraDB RDS for MySQL>')

Example:

INSERT INTO clickhouse_test_table_distributed SELECT * FROM mysql('rm-bp16t9h3999xb****.mysql.rds.aliyuncs.com:3306','testdb','mysql_test_table','test','123456Aa');

Step 4: Query the data imported to the ApsaraDB for ClickHouse cluster

1. Query the data imported to the ApsaraDB for ClickHouse cluster. Enter the following query statement and click Execute(F8) to check whether the data is imported:

   SELECT * FROM clickhouse_test_table_distributed;

   Note

   If you import data to a local table, replace the name of the distributed table clickhouse_test_table_distributed in the query statement with the name of the local table clickhouse_test_table, and execute the query statement.

2. The following query result is returned:

   ┌─v1─┬─v2─┬─v3──┐
   │  4 │  4 │ 4.0 │  
   │  1 │  1 │ 2.0 │ 
   │  1 │  1 │ 0.0 │
   │  4 │  1 │ 2.0 │
   │  7 │  1 │ 3.0 │
   └────┴────┴─────┘

Data type mappings