ClickHouse（十八）数据有限更新

1.概述

使用clickhouse的聚合函数，可以实现数据的有限更新，从而减少使用optimize table带来的性能开销。

2.测试数据表

CREATE TABLE temp.iop_user_profile_list on cluster ck_cluster
(
    `uid` Int64 COMMENT '用户唯一标识',
    `reg_time` DateTime COMMENT '注册时间',
    `nickname` String COMMENT '昵称',
    `phone` String COMMENT '手机号码',
    `part` Int64
)
ENGINE = ReplicatedAggregatingMergeTree('/clickhouse/temp/tables/{shard}/iop_user_profile_list', '{replica}')
partition by part
order by uid
SETTINGS index_granularity = 8192;

CREATE TABLE temp.iop_user_profile_list_all on cluster ck_cluster
as temp.iop_user_profile_list
ENGINE = Distributed('ck_cluster', 'temp', 'iop_user_profile_list', intHash64(uid));


insert into temp.iop_user_profile_list_all(uid, reg_time, nickname, phone, part)
select 123, now(), '小明', '123', 1;

insert into temp.iop_user_profile_list_all(uid, reg_time, nickname, phone, part)
select 123, now(), '小明', '1234', 2;

insert into temp.iop_user_profile_list_all(uid, reg_time, nickname, phone, part)
select 124, now(), '小明', '1234', 2;

3.使用聚合函数

CREATE TABLE temp.iop_user_profile_test on cluster ck_cluster
(
    `uid` Int64 COMMENT '用户唯一标识',
    `reg_time` AggregateFunction(argMaxIf, DateTime, DateTime, UInt8) COMMENT '注册时间',
    `nickname` AggregateFunction(argMaxIf, String, DateTime, UInt8) COMMENT '昵称',
    `phone` AggregateFunction(argMaxIf, String, DateTime, UInt8) COMMENT '手机号码'
)
ENGINE = ReplicatedAggregatingMergeTree('/clickhouse/temp/tables/{shard}/iop_user_profile_test', '{replica}')
ORDER BY uid
SETTINGS index_granularity = 8192;

CREATE TABLE temp.iop_user_profile_test_all on cluster ck_cluster
as temp.iop_user_profile_test
ENGINE = Distributed('ck_cluster', 'temp', 'iop_user_profile_test', intHash64(uid));

从测试表写入数据：
写入也要用聚合函数来实现，选取最大版本保留，数据写入和顺序没有关系，If函数可以用来判断空值然后不写入，写入即可查询，不用optimize table操作。

insert into temp.iop_user_profile_test_all(uid, nickname, reg_time, phone)
SELECT
    uid,
    argMaxIfState(nickname, reg_time, nickname!='') nickname,
    argMaxIfState(reg_time, reg_time, 1=1) reg,
    argMaxIfState(phone,reg_time,phone!='') phone
FROM temp.iop_user_profile_list_all
group by uid;

4.查询结果

select uid,argMaxIfMerge(nickname),
       argMaxIfMerge(reg_time),
       argMaxIfMerge(phone)
       from temp.iop_user_profile_test_all
group by uid;

uid=123，数据已经更新为最新版本的了