clickhouse 行列转换

相关函数请参考官方网站：
https://clickhouse.tech/docs/zh/sql-reference/functions/date-time-functions/

行列转置一般由由行转为列，或者由列转为行。

CREATE TABLE datasets.t_city
(
    `province` String, 
    `city` String, 
    `createtime` DateTime, 
    `city_level` Int8
)
ENGINE = MergeTree()
ORDER BY province
SETTINGS index_granularity = 8192；
 
 
 
insert into t_city values('Hubei','Wuhan',now(),2),('Hubei','Xiangyang',now(),3),('Shanghai','Shanghai',now(),1),('Guangdong','Guangzhou',now(),1),('Guangdong','Shenzhen',now(),1),('Guangdong','DOngguan',now(),2),('Guangdong','Zhuhai',now(),3);
 
 
Clickhouse> select * from t_city;
 
SELECT *
FROM t_city
 
┌─province──┬─city──────┬──────────createtime─┬─city_level─┐
│ Guangdong │ Guangzhou │ 2020-07-07 14:02:53 │          1 │
│ Guangdong │ Shenzhen  │ 2020-07-07 14:02:53 │          1 │
│ Guangdong │ DOngguan  │ 2020-07-07 14:02:53 │          2 │
│ Guangdong │ Zhuhai    │ 2020-07-07 14:02:53 │          3 │
│ Hubei     │ Wuhan     │ 2020-07-07 14:02:53 │          2 │
│ Hubei     │ Xiangyang │ 2020-07-07 14:02:53 │          3 │
│ Shanghai  │ Shanghai  │ 2020-07-07 14:02:53 │          1 │
└───────────┴───────────┴─────────────────────┴────────────┘
 
7 rows in set. Elapsed: 0.002 sec. 
列转行：

查询每个省份用户的城市：

Clickhouse> select province, groupArray(city) from t_city group by province;
 
SELECT 
    province, 
    groupArray(city)
FROM t_city
GROUP BY province
 
┌─province──┬─groupArray(city)─────────────────────────────┐
│ Shanghai  │ ['Shanghai']                                 │
│ Hubei     │ ['Wuhan','Xiangyang']                        │
│ Guangdong │ ['Guangzhou','Shenzhen','Dongguan','Zhuhai'] │
└───────────┴──────────────────────────────────────────────┘
 
 
 
 
插入一条重复的记录：
insert into t_city values('Hubei','Wuhan',now(),2);
 
可以看到Hubei有一个重复的wuhan
 
Clickhouse> select province, groupArray(city) from t_city group by province;
 
SELECT 
    province, 
    groupArray(city)
FROM t_city
GROUP BY province
 
┌─province──┬─groupArray(city)─────────────────────────────┐
│ Shanghai  │ ['Shanghai']                                 │
│ Hubei     │ ['Wuhan','Xiangyang','Wuhan']                │
│ Guangdong │ ['Guangzhou','Shenzhen','Dongguan','Zhuhai'] │
└───────────┴──────────────────────────────────────────────┘
 
3 rows in set. Elapsed: 0.002 sec. 
 
可以使用函数groupUniqArray进行去重：
 
Clickhouse> select province, groupUniqArray(city) from t_city group by province;
 
SELECT 
    province, 
    groupUniqArray(city)
FROM t_city
GROUP BY province
 
┌─province──┬─groupUniqArray(city)─────────────────────────┐
│ Shanghai  │ ['Shanghai']                                 │
│ Hubei     │ ['Wuhan','Xiangyang']                        │
│ Guangdong │ ['Zhuhai','Dongguan','Guangzhou','Shenzhen'] │
└───────────┴──────────────────────────────────────────────┘
 
3 rows in set. Elapsed: 0.003 sec. 
字符串拆分：
 
Clickhouse> select splitByChar('#','Hubei_Wuhan#Hubei_Xiangyang#Guangdong_Shenzhen') col;
 
SELECT splitByChar('#', 'Hubei_Wuhan#Hubei_Xiangyang#Guangdong_Shenzhen') AS col
 
┌─col────────────────────────────────────────────────────┐
│ ['Hubei_Wuhan','Hubei_Xiangyang','Guangdong_Shenzhen'] │
└────────────────────────────────────────────────────────┘
 
1 rows in set. Elapsed: 0.002 sec. 
可以使用ArrayJoin 函数将一行转为行：

Clickhouse> select arrayJoin(splitByChar('#', 'Hubei_Wuhan#Hubei_Xiangyang#Guangdong_Shenzhen')) col;
 
SELECT arrayJoin(splitByChar('#', 'Hubei_Wuhan#Hubei_Xiangyang#Guangdong_Shenzhen')) AS col
 
┌─col────────────────┐
│ Hubei_Wuhan        │
│ Hubei_Xiangyang    │
│ Guangdong_Shenzhen │
└────────────────────┘
 
3 rows in set. Elapsed: 0.002 sec. 
 
 
 
实际示例：
 
SELECT 
    province, 
    groupArray(city)
FROM t_city
GROUP BY province
 
┌─province──┬─groupArray(city)─────────────────────────────┐
│ Shanghai  │ ['Shanghai']                                 │
│ Hubei     │ ['Wuhan','Xiangyang','Wuhan']                │
│ Guangdong │ ['Guangzhou','Shenzhen','Dongguan','Zhuhai'] │
└───────────┴──────────────────────────────────────────────┘
 
3 rows in set. Elapsed: 0.003 sec. 
 
Clickhouse> SELECT     province,     arrayJoin(groupArray(city)) new_city FROM t_city GROUP BY province;
 
SELECT 
    province, 
    arrayJoin(groupArray(city)) AS new_city
FROM t_city
GROUP BY province
 
┌─province──┬─new_city──┐
│ Shanghai  │ Shanghai  │
│ Hubei     │ Wuhan     │
│ Hubei     │ Xiangyang │
│ Hubei     │ Wuhan     │
│ Guangdong │ Guangzhou │
│ Guangdong │ Shenzhen  │
│ Guangdong │ Dongguan  │
│ Guangdong │ Zhuhai    │
└───────────┴───────────┘
 
8 rows in set. Elapsed: 0.003 sec. 
结论：在clickhouse中主要使用两个函数groupArray 和ArrayJoin。