就像在dolphindb中一样，如何在Clickhouse中实现`pivot`

Question

我想对pivot某些数据做一些操作。就像跟随。

>>> df = pd.DataFrame({'foo': ['one', 'one', 'one', 'two', 'two',
...                            'two'],
...                    'bar': ['A', 'B', 'C', 'A', 'B', 'C'],
...                    'baz': [1, 2, 3, 4, 5, 6],
...                    'zoo': ['x', 'y', 'z', 'q', 'w', 't']})
>>> df
    foo   bar  baz  zoo
0   one   A    1    x
1   one   B    2    y
2   one   C    3    z
3   two   A    4    q
4   two   B    5    w
5   two   C    6    t
>>> df.pivot(index='foo', columns='bar', values='baz')
bar  A   B   C
foo
one  1   2   3
two  4   5   6

我知道DolphinDB可以pivot在sql中完成。

    dateValue=2007.08.01
    num=500
    syms = (exec count(*) from taq 
    where 
        date = dateValue, 
        time between 09:30:00 : 15:59:59, 
        0<bid, bid<ofr, ofr<bid*1.2
    group by symbol order by count desc).symbol[0:num]

    priceMatrix = exec avg(bid + ofr)/2.0 as price from taq 
    where 
        date = dateValue, Symbol in syms, 
        0<bid, bid<ofr, ofr<bid*1.2, 
        time between 09:30:00 : 15:59:59 
    pivot by time.minute() as minute, Symbol

但是如何pivot在Clickhouse中做？我应该使用客户端API来获取数据吗？但是行太多了，很难处理很多行。而且如果我不能使用pandas，如何pivot轻松实现操作？

Answer 1

这是可以帮助您开始的初步实施。

备注：

• 不支持行中的“孔”（每列应包含值）

• 转换为通用类型（字符串）的所有列的类型

• 介绍了字段orderNum。它是结果中源列的订单号（例如，“ bar”列为第二列）

• 结果表示为具有Array类型的一列的行。数组项的顺序由orderNum定义。

准备测试数据：

CREATE TABLE test.pivot_test
(    
    orderNum Int,
    s String,
    values Array(String)
) ENGINE = Memory;

INSERT INTO test.pivot_test
VALUES 
  (1, 'foo', ['one', 'one', 'one', 'two', 'two', 'two']),
  (3, 'baz', ['1', '2', '3', '4', '5', '6']),
  (4, 'zoo', ['x', 'y', 'z', 'q', 'w', 't']),
  (2, 'bar', ['A', 'B', 'C', 'A', 'B', 'C']);

/* 
The content of table test.pivot_test:

??orderNum???s?????values?????????????????????????????????
?        1 ? foo ? ['one','one','one','two','two','two'] ?
?        3 ? baz ? ['1','2','3','4','5','6']             ?
?        4 ? zoo ? ['x','y','z','q','w','t']             ?
?        2 ? bar ? ['A','B','C','A','B','C']             ?
??????????????????????????????????????????????????????????
*/

枢轴模拟：

SELECT arrayMap(x -> x.1, arraySort(x -> x.2, groupArray(value_ordernum))) as row
FROM
(
    SELECT
        (value, orderNum) AS value_ordernum,
        value_index
    FROM test.pivot_test
    ARRAY JOIN
        values AS value,
        arrayEnumerate(values) AS value_index
  /*
    The result of execution the nested query:

    ??value_ordernum???value_index??
    ? ('one',1)      ?           1 ?
    ? ('one',1)      ?           2 ?
    ? ('one',1)      ?           3 ?
    ? ('two',1)      ?           4 ?
    ? ('two',1)      ?           5 ?
    ? ('two',1)      ?           6 ?
    ? ('1',3)        ?           1 ?
    ? ('2',3)        ?           2 ?
    ? ('3',3)        ?           3 ?
    ? ('4',3)        ?           4 ?
    ? ('5',3)        ?           5 ?
    ? ('6',3)        ?           6 ?
    ? ('x',4)        ?           1 ?
    ? ('y',4)        ?           2 ?
    ? ('z',4)        ?           3 ?
    ? ('q',4)        ?           4 ?
    ? ('w',4)        ?           5 ?
    ? ('t',4)        ?           6 ?
    ? ('A',2)        ?           1 ?
    ? ('B',2)        ?           2 ?
    ? ('C',2)        ?           3 ?
    ? ('A',2)        ?           4 ?
    ? ('B',2)        ?           5 ?
    ? ('C',2)        ?           6 ?
    ????????????????????????????????  
  */
)
GROUP BY value_index;

/*
The final result:

??row??????????????????
? ['two','A','4','q'] ?
? ['one','C','3','z'] ?
? ['one','B','2','y'] ?
? ['two','B','5','w'] ?
? ['one','A','1','x'] ?
? ['two','C','6','t'] ?
???????????????????????
*/