用於在Vertica中連接字符串的聚合函數

Question

在vertica中有一個表：像這樣測試：

ID     |   name
1      |    AA
2      |    AB
2      |    AC
3      |    AD
3      |    AE
3      |    AF

我怎么能使用聚合函數或如何編寫查詢來獲取這樣的數據（vertica語法）？

ID    |  ag
1     |  AA
2     |  AB, AC
3     |  AD, AE, AF 

Answer 1

首先，您需要為agg_concatenate編譯agg_concatenate 。

-- Shell commands
cd /opt/vertica/sdk/examples/AggregateFunctions/
g++ -D HAVE_LONG_INT_64 -I /opt/vertica/sdk/include -Wall -shared -Wno-unused-value -fPIC -o Concatenate.so Concatenate.cpp /opt/vertica/sdk/include/Vertica.cpp

-- vsql commands
CREATE LIBRARY AggregateFunctionsConcatenate AS '/opt/vertica/sdk/examples/AggregateFunctions/Concatenate.so';
CREATE AGGREGATE FUNCTION agg_concatenate AS LANGUAGE 'C++' NAME 'ConcatenateFactory' LIBRARY AggregateFunctionsConcatenate;

然后你可以進行如下查詢：

select id, rtrim(agg_concatenate(name || ', '),', ') ag
from mytable
group by 1
order by 1

使用rtrim擺脫最后的'，'。

如果您需要以某種方式對聚合進行排序，則可能需要在內聯視圖中選擇/排序或使用first。

Answer 2

SELECT id,
    MAX(DECODE(row_number, 1, a.name)) ||
    NVL(MAX(DECODE(row_number, 2, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 3, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 4, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 5, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 6, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 7, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 8, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 9, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 10, ',' || a.name)), '')||
    NVL(MAX(DECODE(row_number, 11, ',' || a.name)), '') ||
    NVL(MAX(DECODE(row_number, 12, ',' || a.name)), '') ag
FROM
    (SELECT id, name, ROW_NUMBER() OVER(PARTITION BY name ORDER BY id) row_number FROM test) a
GROUP BY a.id
ORDER BY a.id;

Answer 3

另一種方法是使用github上的strings包中的 GROUP_CONCAT 。

select id, group_concat(name) over (partition by id order by name) ag
from mytable

但是這種方法存在一些限制，因為分析udx不允許您包含其他聚合（並且您必須內聯它或使用它來向其添加更多數據）。