Oracle 18c

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create table tab (stringval varchar2(100));
alter session set plsql_warnings='enable:7204';
create or replace procedure proc is
    Num number;
    Str varchar2(100);
begin
    Num := 10;
    select stringval into Str
    from tab
    where stringval = Num;
end;
/
select * from user_errors where name ='PROC';


NAME
TYPE
SEQUENCE
LINE
POSITION
TEXT
ATTRIBUTE
MESSAGE_NUMBER


PROC
PROCEDURE
1
8
11
PLW-07204: conversion away from column type may result in sub-optimal query plan
WARNING
7204