Question

在vertica中有一个表：像这样测试：

class Country(models.Model):
    name = models.CharField(max_lenght=200)

我如何使用聚合函数或如何编写查询来获取这样的数据（vertica语法）？

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

Answer 1

首先，您需要为agg_concatenate编译udx。

-- 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;

然后你可以进行如下查询：

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

使用rtrim摆脱最后的'，'。

如果您需要以某种方式对聚合进行排序，则可能需要在内联视图中选择/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

另一种方法是使用strings package on github中的GROUP_CONCAT。

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

然而，此方法存在一些限制，因为分析udx不允许您包含其他聚合（并且您必须内联它或使用它来向其添加更多数据）。

用于在Vertica中连接字符串的聚合函数

3 个答案: