使用ClickHouse表函数将MySQL数据导入到ClickHouse

#clickhouse-client
:create database dw;
:use dw;

--导入数据：
CREATE TABLE Orders ENGINE = MergeTree ORDER BY OrderID AS SELECT * FROM mysql('10.42.134.136:4000', 'dw', 'Orders', 'root', 'xyz');

CREATE TABLE Orders
ENGINE = MergeTree
ORDER BY OrderID AS
SELECT *
FROM mysql('10.42.134.136:4000', 'dw', 'FactSaleOrders', 'root', 'xyz') 

Ok.

 rows in set. Elapsed: 1832.114 sec. Processed 85.71 million rows, 65.27 GB (46.78 thousand rows/s., 35.62 MB/s.)
解释：导入数据8571万行，耗时1832.,总大小65.27GB 最后一次每秒4.678万行导入,每秒导入35.62MB的数据。

前提条件：
MySQL的主键必须为not null
10.42.134.136: 为MySQL的IP地址和端口号
dw 为MySQL的库，作为数据源的
Orders 为MySQL的表，源表
root为MySQL的账号
xyz为MySQL的账号对应的密码 账号需要具备远程连接访问的权限。

注意：
.order by 后的字段大小写要和MySQL的大小写一样
.主键列在MySQL中必须定义为NOT NULL
报错：DB::Exception: Sorting key cannot contain nullable columns.

.导入速度和mysql的列有关，若列较少导入的更快，和硬件的读取写入速度，网络带宽也有影响。
.支持从TiDB和MySQL直接读取数据。

注意ClickHouse创建的表映射，经过操作发现对于MySQL的Deciaml类型的不能映射到ClickHouse中，ClickHouse映射的类型是String类型了

可以使用一下方法快速创建映射表并导入数据，还有有其他方法的大神留言

第一步创建Mysql到CLickhouse的映射表插入1条数据，这里可以随表
CREATE TABLE Orders ENGINE = MergeTree ORDER BY OrderID AS SELECT * FROM mysql('10.42.134.136:4000', 'dw', 'Orders', 'root', 'xyz') limit 1;
第二步查询创建的表结构复制下来
show create table Orders；
第三部删除表
drop table Orders;
第四部将第二步复制的表结构里的Decimal字段类型进行变更然后执行即可
第五部插入数据
insert into Orders SELECT * FROM mysql('10.42.134.136:4000', 'dw', 'Orders', 'root', 'xyz');

字段映射表

ClickHouse	MySQL	Comment
UInt8, UInt16, UInt32, UInt64	TINYINT UNSIGNED, SMALLINT UNSIGNED, INT UNSIGNED, BIGINT UNSIGNED
Int8, Int16, Int32, Int64	TINYINT SIGNED, SMALLINT SIGNED, INT SIGNED, BIGINT SIGNED
Float32, Float64	FLOAT, DOUBLE	Supports inf, -inf, nan, recommended NOT to use by ClickHouse!
String	BLOB, TEXT, VARCHAR, VARBINARY	No encoding. Recommended to use UTF-8. In fact behaves like a BLOB.
FixedString(n)	CHAR, BINARY	\0 padded. Less functions available than String, in fact it behaves like BINARY.
Date	DATE	UNIX epoch date up to 2038.
DateTime	DATETIME, TIMESTAMP	UNIX epoch timestamp up to 2038.
Enum	ENUM	Similar to MySQL ENUM. Behaves like Int8/16.
Array(type)	n.a.	Array of type. Closest equivalent in MySQL is JSON? Not well supported.
Tuple()	n.a.
Nested()	n.a.	Closest equivalent in MySQL is JSON?
AggregateFunction()	n.a.
Set	n.a.
Expression	n.a.