根据行中的其他值更新列

Question

请考虑下trials表:

CREATE TABLE trials
(
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
name_A VARCHAR(6),
name_B VARCHAR(6),
score_A INT,
score_B INT);

抽象地说,这代表了一系列试验,其中尝试了两种可能的东西,A和B. A和B各得一分.

后来我们增加两列winner和loser,两者相同的数据类型为name_A和name_B:

ALTER TABLE trials
ADD COLUMN winner VARCHAR(6),
ADD COLUMN loser VARCHAR(6);

对于每个试验,我们希望填写winner与较高分数对应的任何名称.

例如,如果试用了

???????????????????????????????????????
? name_A ? name_B ? score_A ? score_B ?
???????????????????????????????????????
? alice  ? bob    ? 10      ? 5       ?
???????????????????????????????????????

那个试验winner应该是alice.同样,在这种情况下loser应该填充bob:

????????????????????????????????????????????????????????
? name_A ? name_B ? score_A ? score_B ? winner ? loser ?
????????????????????????????????????????????????????????
? alice  ? bob    ? 10      ? 5       ? alice  ? bob   ?
????????????????????????????????????????????????????????

如何UPDATE正确设置表中的赢家和输家列trials？

---

尝试:

我考虑过使用子查询.这是一个查找赢家和输家的子查询:

SELECT id, name_A AS winner, name_B AS loser
  FROM trials
  WHERE score_A > score_B
  UNION
  SELECT id, name_B AS winner, name_A AS loser
  FROM trials
  WHERE score_B > score_A)

为了获得胜利者,我做到了这一点:

UPDATE trials SET winner=(
  SELECT id, winner from (  
    SELECT id, name_A AS winner
      FROM trials
      WHERE score_A > score_B
    UNION
    SELECT id, name_B AS winner
      FROM trials
      WHERE score_B > score_A) AS temp
  )
  WHERE temp.id = trials.id;

但它不起作用,因为该字段temp.id未被识别.

Answer 1

您可以在没有子查询的情况下创建它:

查询:

UPDATE test.trials AS t
SET t.winner=CASE WHEN t.score_A > t.score_B THEN t.name_A
                  WHEN t.score_A < t.score_B THEN t.name_B
             ELSE NULL END,
    t.loser=CASE WHEN t.score_A > t.score_B THEN t.name_B
                  WHEN t.score_A < t.score_B THEN t.name_A
             ELSE NULL END;

测试:

创建表格:

CREATE TABLE trials
    (id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
    name_A VARCHAR(6),
    name_B VARCHAR(6),
    score_A INT,
    score_B INT);

空表:

SELECT * FROM test.trials;

测试数据:

INSERT INTO test.trials (id, name_A, name_B, score_A, score_B) VALUES ('1', 'alice', 'bob', '10', '5');
INSERT INTO test.trials (id, name_A, name_B, score_A, score_B) VALUES ('2', 'onare', 'some', '5', '11');

SELECT * FROM test.trials;

+----+--------+--------+---------+---------+
| id | name_A | name_B | score_A | score_B |
+----+--------+--------+---------+---------+
|  1 | alice  | bob    |      10 |       5 |
|  2 | onare  | some   |       5 |      11 |
+----+--------+--------+---------+---------+

添加winner和loser列:

ALTER TABLE test.trials 
    ADD COLUMN winner VARCHAR(10) NULL COMMENT '' AFTER score_B,
    ADD COLUMN loser VARCHAR(10) NULL COMMENT '' AFTER winner;

SELECT * FROM test.trials;

+----+--------+--------+---------+---------+--------+-------+
| id | name_A | name_B | score_A | score_B | winner | loser |
+----+--------+--------+---------+---------+--------+-------+
|  1 | alice  | bob    |      10 |       5 | NULL   | NULL  |
|  2 | onare  | some   |       5 |      11 | NULL   | NULL  |
+----+--------+--------+---------+---------+--------+-------+

运行查询:

UPDATE test.trials AS t
    SET t.winner=CASE WHEN t.score_A > t.score_B THEN t.name_A
    WHEN t.score_A < t.score_B THEN t.name_B
    ELSE NULL END,
    t.loser=CASE WHEN t.score_A > t.score_B THEN t.name_B
    WHEN t.score_A < t.score_B THEN t.name_A
    ELSE NULL END;


SELECT * FROM test.trials;

+----+--------+--------+---------+---------+--------+-------+
| id | name_A | name_B | score_A | score_B | winner | loser |
+----+--------+--------+---------+---------+--------+-------+
|  1 | alice  | bob    |      10 |       5 | alice  | bob   |
|  2 | onare  | some   |       5 |      11 | some   | onare |
+----+--------+--------+---------+---------+--------+-------+

你甚至可以使用IFon winner和loser.我用过,CASE因为如果score_A和之间有匹配score_B,你想要查询做什么？添加新列match.

Answer 2

UPDATE Trials
SET Winner =
    CASE
        WHEN score_A > score_B THEN name_A
        WHEN score_B > score_A THEN name_B
        ELSE NULL
        END