我需要构建一个单一的触发器，当一个飞行员已经被分配到一个章程时，分配一个飞行员作为副驾驶员

Question

DROP TRIGGER IF EXISTS COPILOT_ASSIGNED; 

DELIMITER // 
CREATE TRIGGER COPILOT_ASSIGNED 
    BEFORE INSERT ON crew 
    FOR EACH ROW 
BEGIN 
    IF CHAR_TRIP EXISTS AND CREW_JOB = 'Pilot' 
    THEN SET NEW.CREW_JOB = 'Copilot'; 
    END IF; 
END // 
DELIMITER ; 

INSERT INTO crew VALUES (10019, 109, 'Pilot'); 
INSERT INTO crew VALUES (10019, 106, 'Pilot'); 

SELECT * FROM crew WHERE CHAR_TRIP = 10019; 

我无法确定如何写这个触发器。我需要检查一下包机（CREW_TRIP）是否已经被分配了一个飞行员（CREW_JOB）。如果是这样，则需要将试点改为副驾驶（CREW_JOB）。

Answer 1

DROP TRIGGER IF EXISTS COPILOT_ASSIGNED; 

DELIMITER // 
CREATE TRIGGER COPILOT_ASSIGNED 
    BEFORE INSERT ON crew 
    FOR EACH ROW 
BEGIN 
    IF EXISTS (SELECT * FROM crew WHERE CHAR_TRIP = NEW.CHAR_TRIP AND 
CREW_JOB='Pilot') 
    THEN SET NEW.CREW_JOB = 'Copilot'; 
    END IF; 
END // 
DELIMITER ; 

INSERT INTO crew VALUES (10019, 109, 'Pilot'); 
INSERT INTO crew VALUES (10019, 106, 'Pilot');