3 improved formatting
source | link

  INSERT INTO merchant_seq VALUES (NULL);
  SET @last_ID = (SELECT MAX(merchant_id) FROM merchant_seq);
  SET NEW.merchant_id = CONCAT('MC', LPAD(@last_ID, 10, '0'));
INSERT INTO merchant_seq VALUES (NULL);
SET @last_ID = (SELECT MAX(merchant_id) FROM merchant_seq);
SET NEW.merchant_id = CONCAT('MC', LPAD(@last_ID, 10, '0'));

  INSERT INTO merchant_seq VALUES (NULL);
  SET @last_ID = (SELECT MAX(merchant_id) FROM merchant_seq);
  SET NEW.merchant_id = CONCAT('MC', LPAD(@last_ID, 10, '0'));
INSERT INTO merchant_seq VALUES (NULL);
SET @last_ID = (SELECT MAX(merchant_id) FROM merchant_seq);
SET NEW.merchant_id = CONCAT('MC', LPAD(@last_ID, 10, '0'));
2 added 55 characters in body
source | link
replace 

  INSERT INTO merchant_seq VALUES (NULL);
  SET NEW.merchant_id = CONCAT('MC', LPAD(LAST_INSERT_ID(), 10, '0'));
 INSERT INTO merchant_seq VALUES (NULL);
with  SET @last_ID = (SELECT MAX(merchant_id) FROM merchant_seq);

  INSERT INTO merchant_seq VALUES (CONCAT('MC', LPAD(LAST_INSERT_ID(), 10, '0')));
  SET NEW.merchant_id = CONCAT('MC', LPAD(@last_ID, 10, '0'));
replace 

  INSERT INTO merchant_seq VALUES (NULL);
  SET NEW.merchant_id = CONCAT('MC', LPAD(LAST_INSERT_ID(), 10, '0'));

with 

  INSERT INTO merchant_seq VALUES (CONCAT('MC', LPAD(LAST_INSERT_ID(), 10, '0')));

  INSERT INTO merchant_seq VALUES (NULL);
  SET @last_ID = (SELECT MAX(merchant_id) FROM merchant_seq);
  SET NEW.merchant_id = CONCAT('MC', LPAD(@last_ID, 10, '0'));
1
source | link

replace 

  INSERT INTO merchant_seq VALUES (NULL);
  SET NEW.merchant_id = CONCAT('MC', LPAD(LAST_INSERT_ID(), 10, '0'));

with 

  INSERT INTO merchant_seq VALUES (CONCAT('MC', LPAD(LAST_INSERT_ID(), 10, '0')));