如何从字符串中找到每三个单词

Question

我正在尝试创建一个接受字符串作为参数的函数，如下例所示

this is a sample string and i need to use uppercase letter for every third word in this string

以及如何获得如下输出

position;word
-------------
3       ;"a"
6       ;"and"
9       ;"to"
12      ;"letter"
15      ;"third"
18      ;"this"

我知道如何创建函数，但我找不到找到所需输出的方法

create or replace function fn_every_third(str text) returns table(pos bigint,wrd text) as
$$
--code to get the output
$$
language sql

Answer 1

create or replace function fn_every_third(str text) returns table(pos bigint,wrd text) as
$$
with cte as(
select  * from(
select row_number() over() rn,word from(
select unnest(regexp_split_to_array(str,' ')) word)t)q
)
select rn ,word from cte 
where rn in (select generate_series(3,(select max(rn) from cte),3))
order by rn 
$$
language sql

用途：

select * 
from fn_every_third('this is a sample string and i need to use uppercase letter for every third word in this string')

---

参考：

• row_number() over()(Window Functions)
• regexp_split_to_array()
• generate_series()
• WITH Queries
• unnest()