INSERT INTO tb (name, date, stat1, stat2, stat3)
VALUES (?, ?, ?, ?, ?)
ON DUPLICATE KEY UPDATE stat1 = stat1 + VALUES(stat1), stat2 = stat2 + VALUES(stat2), stat3 = stat3 + VALUES(stat3)

Well, this is old. But of course you only need to provide a value once, there's no reason to add it a second time in the query (which comes in handy for multiple inserts, or prepared statements):

INSERT INTO table1
  (col1, col2, col3, col4)
VALUES
  ('val1', 'val2', 'val3', 'val4')
ON DUPLICATE KEY UPDATE
  col2=VALUES(col2),
  col3=VALUES(col3) [,...]

Which has as advantage it will still work for a multiple insert statement:

INSERT INTO table1
  (col1, col2, col3, col4)
VALUES
  ('val1', 'val2', 'val3', 'val4'),
  ('val5', 'val6', 'val7', 'val8'),
  ('val9', 'val10', 'val11', 'val12')
ON DUPLICATE KEY UPDATE
  col2=VALUES(col2),
  col3=VALUES(col3) [,...]

A modern PHP example:

$sql = "INSERT INTO table1 (col1, col2, col3, col4) VALUES (?,?,?,?)
        ON DUPLICATE KEY UPDATE
        col2=VALUES(col2),
        col3=VALUES(col3),
        col4=VALUES(col4)";
$db->prepare($sql)->execute([$val1, $val2, $val3, $val4]);

Consider

INSERT INTO table (a,b,c) VALUES (1,2,3)
    -> ON DUPLICATE KEY UPDATE c=c+1;

If a and b are UNIQUE fields, UPDATE occurs on a = 1 OR b = 2. Also when condition a = 1 OR b = 2 is met by two or more entries, update is done only once.

Ex here table table with Id and Name UNIQUE fields

Id     Name     Value 
1      P        2 
2      C        3 
3      D        29 
4      A        6

If query is

INSERT INTO table (Id, Name, Value)
VALUES (1, C, 7);

then we get

Id     Name     Value 
1      P        2 
2      C        3 
3      D        29 
4      A        6
1      C        7

which violates uniqueness of Id and Name. Now with

INSERT INTO table (Id, Name, Value)
VALUES (1, C, 7)
ON DUPLICATE KEY UPDATE Value = 7;

we get

Id     Name     Value 
1      P        7 
2      C        7 
3      D        29 
4      A        6

Behavior on multiple keys is the following

UPDATE in ON DUPLICATE KEY UPDATE is performed if one of the UNIQUE field equals the value to be inserted. Here, UPDATE is performed on Id = 1 OR Name = C. It is equivalent to

UPDATE table 
SET Value = 7
WHERE Id = 1 OR Name = C;

What if I want one update only, for either key

Can use UPDATE statement with LIMIT keyword

UPDATE table 
SET Value = 7
WHERE Id = 1 OR Name = C
LIMIT 1;

which will give

Id     Name     Value 
1      P        7 
2      C        3 
3      D        29 
4      A        6

What if I want one update only if values for both keys are matched

One solution is to ALTER TABLE and make the PRIMARY KEY (or uniqueness) work on both fields.

ALTER TABLE table 
DROP PRIMARY KEY,
ADD PRIMARY KEY (Id, Name);

Now, on

INSERT INTO table (Id, Name, Value)
VALUES (1, C, 7)
ON DUPLICATE KEY UPDATE Value = 7;

we get

Id     Name     Value 
1      P        2 
2      C        3 
3      D        29 
4      A        6
1      C        7

since no duplicate (on both keys) is found.

Beginning with MySQL 8.0.19 you can use an alias for that row (see reference).

INSERT INTO beautiful (name, age)
    VALUES
    ('Helen', 24),
    ('Katrina', 21),
    ('Samia', 22),
    ('Hui Ling', 25),
    ('Yumie', 29)
    AS new
ON DUPLICATE KEY UPDATE
    age = new.age
    ...

For earlier versions use the keyword VALUES (see reference, deprecated with MySQL 8.0.20).

INSERT INTO beautiful (name, age)
    VALUES
    ('Helen', 24),
    ('Katrina', 21),
    ('Samia', 22),
    ('Hui Ling', 25),
    ('Yumie', 29)
ON DUPLICATE KEY UPDATE
    age = VALUES(age),
     ...