insert into table from another table without duplicate

CREATE TABLE `src` (
`a` int(11) NOT NULL,
`b` int(11) DEFAULT NULL,
`c` int(11) DEFAULT NULL
)

CREATE TABLE `dest` (
`a` int(11) NOT NULL,
`b` int(11) DEFAULT NULL,
`c` int(11) DEFAULT NULL
)

INSERT INTO dest
SELECT a, b, c
FROM src
WHERE NOT EXISTS(SELECT 1
FROM dest
WHERE (src.a=dest.a AND src.b=dest.b AND src.c = dest.c)
)

INSERT INTO dest
SELECT s.a,s.b,s.c
FROM src s
LEFT JOIN dest d ON (d.a = s.a AND d.b = s.b AND d.c = s.c)
WHERE d.a IS NULL