Question

how to preserve column names on dynamic pivot下面的代码用于创建动态数据透视表。

如果源表不包含数据，则因为create table column list以逗号结尾（没有透视列），所以会发生sql错误。如何解决这个问题，以便返回空表？

要重现，请删除插入命令

insert into sales values ( '2016-1-1', 'Ø 12.3/3mm', 2);
insert into sales values ( '2016-1-1', '+-3,4%/3mm', 52);
insert into sales values ( '2016-1-3', '/3,2m-', 246);

来自代码。

测试用例：

create temp table sales ( saledate date, productname char(20), quantity int );
insert into sales values ( '2016-1-1', 'Ø 12.3/3mm', 2);
insert into sales values ( '2016-1-1', '+-3,4%/3mm', 52);
insert into sales values ( '2016-1-3', '/3,2m-', 246);

do $do$


declare
voter_list text;
begin

create temp table myyk on commit drop as
select saledate as kuupaev,
  format ('"%s"', replace (upper(productname), ' ', '')) as tootjakood,               
  sum(quantity)::int as kogus 
from sales
group by 1,2
;

drop table if exists pivot;

voter_list := (
    select string_agg(distinct tootjakood, ' ' order by tootjakood) from myyk
    );

execute(format('
    create table pivot (
kuupaev date,
        %1$s
    )', (replace(voter_list, ' ', ' integer, ') || ' integer')
));

execute (format($f$

  insert into pivot
        select
           kuupaev,
            %2$s
        from crosstab($ct$
            select
                kuupaev,tootjakood,kogus
            from myyk
            order by 1
            $ct$,$ct$
            select distinct tootjakood
            from myyk
            order by 1
            $ct$
        ) as (
            kuupaev date,
            %4$s
        );$f$,

        replace(voter_list, ' ', ' + '),
        replace(voter_list, ' ', ', '),
        '',
        replace(voter_list, ' ', ' integer, ') || ' integer'  -- 4.
    ));
end; $do$;

select * from pivot;

使用Postgres 9.1。

Answer 1

在DO块体底部插入异常处理程序。您可以默默地忽略错误并创建虚拟pivot表：

...
exception
    when others then
        drop table if exists pivot;
        create table pivot ("No data" text);
end; $do$;

或使用您自己的错误消息引发异常：

...
exception
    when others then
        drop table if exists pivot;
        raise exception 'There is no data in the source dataset.'
end; $do$;

您也可以使用if-then-else语句：

...
drop table if exists pivot;

if (select count(*) from myyk) > 0 then 
    voter_list := (
        select string_agg(distinct tootjakood, ' ' order by tootjakood) from myyk
        );
    ...
    ...
else
    create table pivot ("No data" text);
end if;
end; $do$;

从动态数据库返回空数据是没有数据

1 个答案: