Question

尝试将Teradata bteq SQL脚本转换为redshift SQL。我目前的redshift Postgres版本是8.0.2，redshift版本是1.0.1499。当前版本的redshift不支持rollup（），grouping（）函数。如何克服和解决这种情况。它们的等效红移功能是什么？任何人都可以用一些例子来解释怎么做？

示例Teradata SQL -

select 
PRODUCT_ID,CUST_ID, 
GROUPING (PRODUCT_ID), 
GROUPING (CUST_ID), 
row_number over (order by PRODUCT_ID,CUST_ID) AS "ROW_OUTPUT_NUM"
from products 
group by rollup(PRODUCT_ID,CUST_ID);

需要将上面的sql查询转换为Redshift

Answer 1

如果您使用其他人指出的UNION技术，您将多次扫描基础表。

如果精细级别的GROUPing实际上导致数据大小显着减少，那么更好的解决方案可能是：

create temp table summ1 
as
select PRODUCT_ID,CUST_ID, ...
from products 
group by PRODUCT_ID,CUST_ID;

create temp table summ2
as
select PRODUCT_ID,cast(NULL as INT) AS CUST_ID, ...
from products 
group by PRODUCT_ID;

select * from summ1
union all
select * from summ2
union all
select cast(NULL as INT) AS PRODUCT_ID, cast(NULL as INT) AS CUST_ID, ...
from summ2

Answer 2

手动实施ROLLUP

一旦Redshift当前无法识别ROLLUP子句，则必须以困难的方式实现此分组技术。

带有1个参数的ROLLUP

使用ROLLUP Ex。 PostgreSQL

SELECT column1, aggregate_function(*)
FROM some_table
GROUP BY ROLLUP(column1)

等效的实现方式

-- First, the same GROUP BY without the ROLLUP
-- For efficiency, we will reuse this table
DROP TABLE IF EXISTS tmp_totals;
CREATE TEMP TABLE tmp_totals AS
  SELECT column1, aggregate_function(*) AS total1
  FROM some_table
  GROUP BY column1;

-- Show the table 'tmp_totals'
SELECT * FROM tmp_totals

UNION ALL

-- The aggregation of 'tmp_totals'
SELECT null, aggregate_function(total1) FROM tmp_totals

ORDER BY 1

示例输出

Country  | Sales
-------- | -----
Poland   | 2
Portugal | 4
Ukraine  | 3
null     | 9

带有2个参数的ROLLUP