如何使用sql函数在键值对中搜索特定键并返回其对应的值

Question

Suppose the function is taking two inputs 4 and '3:66,8:54,4:23' , the function should search for 4 in the key value pair '3:66,8:54,4:23' , if key 4 is found then it should return corresponding value of it i,e:23 else it should return empty. How to write the function for it in sql.

Answer 1

You didn't tell us the database product you are using.

In Postgres you can do that using string_to_array() combined with split_part() :

select split_part(x.kv, ':', 2)
from unnest(string_to_array('3:66,8:54,4:23', ',')) as x(kv)
where split_part(x.kv, ':', 1) = '4';

You can put that into a SQL function:

create function get_key_value(p_input text, p_key text)
  returns text
as
$$
    select split_part(x.kv, ':', 2)
    from unnest(string_to_array(p_input, ',')) as x(kv)
    where split_part(x.kv, ':', 1) = p_key;
$$
language sql;

Then use:

select get_key_value(''3:66,8:54,4:23'', '4');