[MySQL] json_valid() function does not exist in PG/YB

[shubham-yb]

Jira Link: DB-13460
MySQL has a function json_valid() which returns 0 or 1 to indicate whether a value is valid JSON.
We do not have an alternative function to do this in PG/YB.

Workaround:

Create the function manually on the target.:

create or replace function json_valid(p_json text)
  returns boolean
as
$$
begin
  return (p_json::json is not null);
exception 
  when others then
     return false;  
end;
$$
language plpgsql
immutable;