MySQL(MyISAM)-将字段更新为来自不同表的两个字段中的任何一个
-
16-09-2020 - |
题
我有两张桌子, t1
和 t2
每列两列 - id_user
和 age
.
如何更新 t1.age
致最伟大的 t1.age
和 t2.age
为匹配ID的和离开 t1.age
不变,如果没有匹配的ID在 t2
.
更新前:
t1 +-------+---+ |id_user|age| +-------+---+ | 1| 5| +-------+---+ | 2| 10| +-------+---+ | 3| 10| +-------+---+ t2 +-------+---+ |id_user|age| +-------+---+ | 2| 12| +-------+---+ | 3| 8| +-------+---+ | 4| 20| +-------+---+
更新后:
t1 +-------+---+ |id_user|age| +-------+---+ | 1| 5| +-------+---+ | 2| 12| +-------+---+ | 3| 10| +-------+---+
解决方案
你可能想试试:
UPDATE t1
JOIN t2 ON (t2.id_user = t1.id_user)
SET t1.age = t2.age
WHERE t2.age > t1.age;
测试用例:
CREATE TABLE t1 (id_user int, age int);
CREATE TABLE t2 (id_user int, age int);
INSERT INTO t1 VALUES (1, 5);
INSERT INTO t1 VALUES (2, 10);
INSERT INTO t1 VALUES (3, 10);
INSERT INTO t2 VALUES (2, 12);
INSERT INTO t2 VALUES (3, 8);
INSERT INTO t2 VALUES (4, 20);
结果:
SELECT * FROM t1;
+---------+------+
| id_user | age |
+---------+------+
| 1 | 5 |
| 2 | 12 |
| 3 | 10 |
+---------+------+
3 rows in set (0.00 sec)
其他提示
UPDATE t1
SET age = T2.age
FROM t1
INNER JOIN t2
ON t2.id_user = t1.id_user
WHERE t2.age > t1.age
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