Oracle 18c

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alter session set plsql_warnings='enable:7204';
create table as_string (string_col varchar2(100));
create or replace procedure as_prc 
is
 nNumber number;
 sStr varchar2(100);
begin
  nNumber := 10;
  select string_col into sStr
  from   as_string
  where  string_col = nNumber;
end;
/
select * from user_errors where name ='AS_PRC';


NAME
TYPE
SEQUENCE
LINE
POSITION
TEXT
ATTRIBUTE
MESSAGE_NUMBER


AS_PRC
PROCEDURE
1
9
10
PLW-07204: conversion away from column type may result in sub-optimal query plan
WARNING
7204