Question

考虑以下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。

稍后我们添加两列winner和loser，两者都与name_A和name_B具有相同的数据类型：

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

对于每个试用版，我们都希望使用与较高分相对应的名称填写winner。

例如，如果试用

╔════════╦════════╦═════════╦═════════╗
║ name_A ║ name_B ║ score_A ║ score_B ║
╠════════╬════════╬═════════╬═════════╣
║ alice  ║ bob    ║ 10      ║ 5       ║
╚════════╩════════╩═════════╩═════════╝

然后该审核winner应为alice。同样，在这种情况下，loser应填充bob：

╔════════╦════════╦═════════╦═════════╦════════╦═══════╗
║ name_A ║ name_B ║ score_A ║ score_B ║ winner ║ loser ║
╠════════╬════════╬═════════╬═════════╬════════╬═══════╣
║ alice  ║ bob    ║ 10      ║ 5       ║ alice  ║ bob   ║
╚════════╩════════╩═════════╩═════════╩════════╩═══════╝

UPDATE如何正确设置trials表中的赢家和输家列？

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)

试图获得胜利者，我这样做了：

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，因为无法识别字段temp.id。

Answer 1

你可以在没有子查询的情况下制作它：

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 |
+----+--------+--------+---------+---------+--------+-------+

您甚至可以在IF和winner上使用loser。我使用了CASE，因为如果score_A和score_B之间匹配，那么您希望查询做什么？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

根据行中的其他值更新列

2 个答案:

查询：

测试：