PL/SQL table mutation and trigger Format

I just started with triggers, I want the trigger to give me the msg error if the new tauxHoraire is 50% greater than the current tauxHoraire (so *1.5 >).

The trigger compiles but I’m getting ORA-04091: table name is mutating, trigger/function may not see it. There might a problem in how I wrote it. Or is the problem somewhere else?

CREATE OR REPLACE TRIGGER restrictionTarifHoraire
BEFORE UPDATE ON RESSOURCESPROJET FOR EACH ROW
DECLARE taux_horaire RESSOURCESPROJET.prixHeure%TYPE;
BEGIN
 Select ressourcesprojet.prixHeure into taux_horaire from ressourcesprojet where prixheure=:new.prixHeure;
    IF taux_horaire > (:NEW.prixHeure * 1.5)
    THEN
        RAISE_APPLICATION_ERROR(-20002, 'Err, new tauxHoraire cant be > than 50% of the current tauxHoraire');
    END IF;
END;

My test:

UPDATE RESSOURCESPROJET
SET prixHeure = 800
WHERE RESSOURCESPROJET.idProjet=3;

Answer

Here is the trigger that will raise error when the prixHeure is greater then (1.5 * current prixHeure).

CREATE OR REPLACE TRIGGER restrictionTarifHoraire
BEFORE UPDATE ON RESSOURCESPROJET FOR EACH ROW
DECLARE
    taux_horaire RESSOURCESPROJET.prixHeure%TYPE;
BEGIN
    IF
     :OLD.prixHeure*1.5 <:NEW.prixHeure
    THEN
        RAISE_APPLICATION_ERROR(-20002, 'Err, new tauxHoraire cant be > than 50% of the current tauxHoraire');
    END IF;
END;

Sample:

create table RESSOURCESPROJET (idProjet number,prixHeure number);
insert into RESSOURCESPROJET values (3,100);

UPDATE RESSOURCESPROJET
SET prixHeure = 800
WHERE RESSOURCESPROJET.idProjet=3;

Error:

Error starting at line : 68 in command -
UPDATE RESSOURCESPROJET
SET prixHeure = 800
WHERE RESSOURCESPROJET.idProjet=3
Error report -
ORA-20002: Err, new tauxHoraire cant be > than 50% of the current tauxHoraire
ORA-06512: at "RESTRICTIONTARIFHORAIRE", line 7
ORA-04088: error during execution of trigger 'RESTRICTIONTARIFHORAIRE'