TOP 1 或 LIMIT 1 在相关子查询中不起作用 - SPS 11

Question

我正在尝试处理一个查询，以填充产品的价格，该产品的价格为零，而以前的记录为非零值。我尝试编写一个简单的相关子查询，但它不起作用。

var_1 = select * from "XYZ"."PRD_TEST" where price <> 0 order by period desc;

var_out = select a.product,a.period, ( select price from :var_1 b where a.product = b.product and a.period > b.period and b.period <> 0 limit 1 ) as price from "XYZ"."PRD_TEST" a;

PRODUCT PERIOD PRICE
A 1 100
A 2 0 - to be filled with 100
A 3 0 - to be filled with 100
A 4 5
A 5 0 - to be filled with 5

我尝试用标量函数替换子查询，但它没有将 table 作为参数。

我尝试使用 Left outer join 和 Row_number 实现输出，但它太昂贵并且运行时间很长。

我正在寻找在子查询中仅获取 1 条记录的最佳选择，就像 TOP 1 一样。

Answer 1

您可以使用这样的标量子查询（select ... 限制 1 在 HANA 中不被视为标量，不幸的是）：

    Do begin

var_1 = select * from (( Select 'A' product, '1' period, '100' price from sys.dummy )
Union ( Select 'A' product, '2' period, '0' price from sys.dummy )
Union ( Select 'A' product, '3' period, '0' price from sys.dummy )
Union ( Select 'A' product, '4' period, '5' price from sys.dummy )
Union ( Select 'A' product, '5' period, '0' price from sys.dummy )) order by period desc;

var_out = ( select a.product,
             a.period, 
            ( select max(price) 
              from :var_1 b 
              where a.product = b.product 
              and a.period > b.period 
              and b.period <> 0 
              and b.period = ( select max(period) from :var_1 c 
                               where a.product = c.product
                                 AND a.period > c.period
                                 and c.period <> 0
                                 and c.price <> 0
              )) as price 
              from :var_1 a where price = '0' )
union (select product, period, price from :var_1 where price <> '0' );

select * from :var_out order by product, period;
end

在 sps12 上测试

评论后添加。你为什么不试试呢？这很简单。因为我很好奇，所以我在我的 HCP 试用实例上尝试了它，大约需要 1 秒才能完成数百万行。我包含了一个 ifnull 以避免在早期没有价格的情况下出现具有空值的行。

编码如下：

drop table var_1;
create column table var_1 as 
(
    select 
      cast ( 'Prod' || prd.GENERATED_PERIOD_START as nvarchar(20) ) product, 
      cast ( per.GENERATED_PERIOD_START as decimal(2)) period,
      cast ( case when rand() < '0.5' then rand() * '100' else '0' end 
             as decimal(5,2)) as price -- ~50% of price is 0
      from series_generate_integer(1,0,1000000/13) as prd,  --~1Mio records
           series_generate_integer(1,0,13) as per --12 periods + period 0 
);
merge delta of var_1;
select * from var_1
 order by product, period 
 limit 100;
do begin sequential execution -- don't let parallel execution influence the runtime-measurement
declare start_timestamp timestamp;
start_timestamp = current_timestamp;
var_out = ( select a.product,
             a.period, 
            ifnull ((select max(price) 
              from var_1 b 
              where a.product = b.product 
              and a.period > b.period 
              and b.period <> 0 
              and b.period = ( select max(period) from var_1 c 
                               where a.product = c.product
                                 AND a.period > c.period
                                 and c.period <> 0
                                 and c.price <> 0
              )),'0.0') as price 
              from var_1 a where price = '0' )
union (select product, period, price from var_1 where price <> '0' );

select nano100_between(:start_timestamp, (select current_timestamp from dummy) )/10000 as runtime_millisec from dummy;

select * from :var_out
 order by product, period 
 limit 100;
end

TOP 1 或 LIMIT 1 在相关子查询中不起作用 - SPS 11

TOP 1 or LIMIT 1 not working in a Correlated Subquery - SPS 11

sql

hana