sql - PostgreSQL:如果条件存在则选择所有具有条件的行，否则忽略条件并选择最早的行

Question

我有一个 PostgreSQL 函数 find_all_records_with_params() 返回一个 SETOF 记录。记录表包含以下列:

table records(
id integer,
type integer,
created date,
content text
);

我想选择 current_date - created 大于 90 天的所有记录。但是，如果此查询不存在，我想选择 1 条具有最早 created 日期的记录。

我尝试使用递归 cte(如下所示)来执行此操作，但它不允许使用 if/else 逻辑。我试图避免两次调用 find_all_records_with_params() 函数，并且我不希望尽可能创建临时表。

with most_records as (select * from find_all_records_with_params()),
filtered_records as (select * from most_records where current_date - created > 90)
if exists(select * from filtered_records) then
select * from filtered_records;
else
select * from most_records order by created asc limit 1;
end if;

Answer 1

with most_records as (select * from find_all_records_with_params()),
filtered_records as (select * from most_records where current_date - created > 90)
select * from filtered_records
union 
select * from 
(select * from most_records 
where not exists (select * from filtered_records limit 1) 
order by created asc limit 1 ) a ;

我已经使用联合查询来实现您需要的结果。如果您的 filtered_records 返回结果，则联合后的查询将不会产生任何结果，否则联合产生结果后的查询。