我需要从两个领域获得最大价值:
SELECT MAX(field1), MAX(field2)
现在,我怎样才能从这两个中获得最大价值?
答案 0 :(得分:140)
您可能想要使用GREATEST()
功能:
SELECT GREATEST(field1, field2);
如果要从所有行获得绝对最大值,则可能需要使用以下内容:
SELECT GREATEST(MAX(field1), MAX(field2));
示例1:
SELECT GREATEST(1, 2);
+----------------+
| GREATEST(1, 2) |
+----------------+
| 2 |
+----------------+
1 row in set (0.00 sec)
示例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)
答案 1 :(得分:27)
如果您为每一行选择GREATEST()
SELECT GREATEST(field1, field2)
如果其中一个字段为NULL,它将返回 NULL 。您可以使用IFNULL来解决这个问题
SELECT GREATEST(IFNULL(field1, 0), IFNULL(field2, 0))
答案 2 :(得分:6)
mysql> SELECT GREATEST(2,0);
-> 2
所以,试试:
mysql> SELECT GREATEST(MAX(field1), MAX(field2));
答案 3 :(得分:0)
SELECT max( CASE
WHEN field1 > field2 THEN field1
ELSE field2
END ) as biggestvalue
FROM YourTable;
答案 4 :(得分:0)
将GREATEST / LEAST与MIN / MAX结合使用
GREATEST / LEAST :当您要从各个列中查找最大值或最小值时,可与这些列一起使用。
MIN / MAX :与行一起使用,当您要从各个行中查找最大值或最小值时:
示例表:
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