Check out example codes for "trigger before insert". It will help you in understanding the concepts better.

Code Example 1

DELIMITER $$

CREATE TRIGGER before_workcenters_insert
BEFORE INSERT
ON WorkCenters FOR EACH ROW
BEGIN
    DECLARE rowcount INT;
    
    SELECT COUNT(*) 
    INTO rowcount
    FROM WorkCenterStats;
    
    IF rowcount > 0 THEN
        UPDATE WorkCenterStats
        SET totalCapacity = totalCapacity + new.capacity;
    ELSE
        INSERT INTO WorkCenterStats(totalCapacity)
        VALUES(new.capacity);
    END IF; 

END $$

DELIMITER ;

Code Example 2

CREATE TRIGGER trigger_name
BEFORE INSERT
   ON table_name FOR EACH ROW

BEGIN

   -- variable declarations

   -- trigger code

END;

Code Example 3

INSERT INTO WorkCenters(name, capacity)
VALUES('Mold Machine',100);

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