Redshift 不支持 rollup()、grouping() 函數

Question

嘗試將 Teradata bteq SQL 腳本轉換為 redshift SQL。 我當前的紅移 Postgres 版本是 8.0.2，紅移版本是 1.0.1499。 當前版本的 redshift 不支持 rollup()、grouping() 函數。 如何克服和解決這種情況。 它們的等效紅移函數是什么？ 誰能用一些例子來解釋怎么做？

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);

需要將上面的 sql 查詢轉換為 Redshift

Answer 1

如果您使用其他人指出的 UNION 技術，您將多次掃描底層表。

如果精細級別的分組實際上導致數據大小的顯着減少，則更好的解決方案可能是：

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

手動實現 ROLLUP

一旦 Redshift 當前無法識別 ROLLUP 子句，您就必須以艱難的方式實現這種分組技術。

帶 1 個參數的 ROLLUP

與 ROLLUP Ex。 PostgreSQL

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

等效實現

-- 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

示例輸出

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

帶 2 個參數的 ROLLUP

與 ROLLUP Ex。 PostgreSQL

SELECT column1, column2, aggregate_function(*)
FROM some_table
GROUP BY ROLLUP(column1, column2);

等效實現

-- 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, column2, aggregate_function(*) AS total1
  FROM some_table
  GROUP BY column1, column2;

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

UNION ALL

-- The sub-totals of the first category
SELECT column1, null, sum(total1) FROM tmp_totals GROUP BY column1

UNION ALL

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

ORDER BY 1, 2;

示例輸出

Country  | Segment  | Sales
-------- | -------- | -----
Poland   | Premium  | 0
Poland   | Base     | 2
Poland   | null     | 2     <- sub total
Portugal | Premium  | 1
Portugal | Base     | 3
Portugal | null     | 4     <- sub total
Ukraine  | Premium  | 1
Ukraine  | Base     | 2
Ukraine  | null     | 3     <- sub total
null     | null     | 9     <- grand total