Biggest value from two or more fields

mysql> SELECT GREATEST(2,0);
        -> 2

So, try:

mysql> SELECT GREATEST(MAX(field1), MAX(field2));

Use of GREATEST/LEAST with MIN/MAX

GREATEST/LEAST: used with the columns, when you want to find the max or min value from the various columns.

MIN/MAX: used with the rows, when you want to find the max or min value from the various rows:

Example table:

SELECT GREATEST(col_a, col_b, col_c) FROM temp;

SELECT MIN(GREATEST(col_a, col_b, col_c)) FROM temp; # 3 as output
SELECT MAX(GREATEST(col_a, col_b, col_c)) FROM temp; # 9 as output


SELECT LEAST(col_a, col_b, col_c) FROM temp;

SELECT MIN(LEAST(col_a, col_b, col_c)) FROM temp; # 1 as output
SELECT MAX(LEAST(col_a, col_b, col_c)) FROM temp; # 7 as output

You may want to use the GREATEST() function:

SELECT GREATEST(field1, field2);

If you want to get the absolute maximum from all the rows, then you may want to use the following:

SELECT GREATEST(MAX(field1), MAX(field2));

Example 1:

SELECT GREATEST(1, 2);
+----------------+
| GREATEST(1, 2) |
+----------------+
|              2 |
+----------------+
1 row in set (0.00 sec)

Example 2:

CREATE TABLE a (a int, b int);

INSERT INTO a VALUES (1, 1);
INSERT INTO a VALUES (2, 1);
INSERT INTO a VALUES (3, 1);
INSERT INTO a VALUES (1, 2);
INSERT INTO a VALUES (1, 4);

SELECT GREATEST(MAX(a), MAX(b)) FROM a;
+--------------------------+
| GREATEST(MAX(a), MAX(b)) |
+--------------------------+
|                        4 |
+--------------------------+
1 row in set (0.02 sec)

In case you're selecting the GREATEST() for each row

SELECT GREATEST(field1, field2)

It will return NULL if one of the fields is NULL. You could use IFNULL to solve this

SELECT GREATEST(IFNULL(field1, 0), IFNULL(field2, 0))