Columns named old/new of other tables are resolved as the OLD/NEW row inside trigger bodies, giving ER_TRG_NO_SUCH_ROW_IN_TRG and ER_ILLEGAL_PARAMETER_DATA_TYPES2_FOR_OPERATION

CREATE TABLE t (old INT);

CREATE TABLE t1 (a INT);

CREATE TRIGGER tr BEFORE INSERT ON t1 FOR EACH ROW SELECT old FROM t INTO @x;

-- ERROR 1363 (HY000): There is no OLD row in on INSERT trigger

CREATE TABLE t (new INT);

CREATE TABLE t1 (a INT);

CREATE TRIGGER tr BEFORE INSERT ON t1 FOR EACH ROW UPDATE t SET new = new + 1;

INSERT INTO t1 VALUES (1);

-- ERROR 4078 (HY000): Illegal parameter data types row and int for operation '+'