Question

问题

我想清理一个混乱的数据库，并替换对重复条目的引用。在这个定制的示例中（我的要复杂得多），我有两个表：

章鱼
颜色

我们知道：

章鱼具有颜色。
表colors中包含重复项
某些章鱼的颜色可能与其他章鱼相同，但color_id不同。

我解决此问题的方式涉及TEMPORARY表。为避免该错误：

Can't Reopen Table 'duplicates'

我只是多次复制我的TEMPORARY表：

CREATE TEMPORARY TABLE duplicates1 SELECT * FROM duplicates;
CREATE TEMPORARY TABLE duplicates2 SELECT * FROM duplicates;

问题

我想避免克隆TEMPORARY表。

数据

CREATE TABLE `test`.`octopuses` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(45) NOT NULL,
  `color_id` INT NOT NULL,
  PRIMARY KEY (`id`));

CREATE TABLE `test`.`colors` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `name` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`id`));

某些颜色重复：

INSERT INTO colors (name) VALUES
    ('cream'), ('sepia'), ('daffodil'), ('lipstick'),                        
    ('lipstick'), ('garnet'), ('flamingo'), ('navy'),                        
    ('chartreuse'), ('garnet'), ('flamingo'), ('juniper'),                             
    ('flint'), ('flint'), ('charcoal'), ('garnet');

还有一些章鱼：

INSERT INTO octopuses (name, color_id) VALUES
    ('Bubbles', 1), ('Inky', 8), ('Octavius', 1),
    ('Sir Inks-A-Lot', 7), ('Octavia', 16), ('Kraken', 6),
    ('Oncho', 15), ('Big Floppy Sea Spider', 14), ('Calamari', 2),
    ('Scuba Doo', 13), ('Squidward Tentacles', 5), ('Wiggleton', 9),
    ('Cthulhu', 2), ('Octopussy', 3), ('Triton', 10), 
    ('Doctor Octopus', 11), ('Billy The Squid', 4), ('Stretch', 12);

示例

要解决此问题，我首先创建重复列表：

CREATE TEMPORARY TABLE duplicates SELECT
    *, COUNT(*) AS count
FROM
    colors
GROUP BY name
HAVING count > 1;

这里是：

mysql> select * FROM duplicates;
+----+----------+-------+
| id | name     | count |
+----+----------+-------+
|  4 | lipstick |     2 |
|  6 | garnet   |     3 |
|  7 | flamingo |     2 |
| 13 | flint    |     2 |
+----+----------+-------+

然后我想创建一个对应的表，其中我有一个重复的id和一个id要替换为：

CREATE TEMPORARY TABLE duplicates1 SELECT * FROM duplicates;
CREATE TEMPORARY TABLE duplicates2 SELECT * FROM duplicates;

CREATE TEMPORARY TABLE corresponding SELECT
    id, name,
    (SELECT
            id
        FROM
            duplicates2
        WHERE
            duplicates2.name = colors.name) AS first_id
FROM
    colors
WHERE
    name IN (SELECT
            name
        FROM
            duplicates)
        AND id NOT IN (SELECT
            id
        FROM
            duplicates1)
ORDER BY name ASC;

这里的内容：

mysql> SELECT * FROM corresponding;
+----+----------+----------+
| id | name     | first_id |
+----+----------+----------+
| 11 | flamingo |        7 |
| 14 | flint    |       13 |
| 10 | garnet   |        6 |
| 16 | garnet   |        6 |
|  5 | lipstick |        4 |
+----+----------+----------+

然后我只需更新octopuses表：

CREATE TEMPORARY TABLE corresponding1 SELECT * FROM corresponding;

UPDATE octopuses
SET
    color_id = (SELECT
            first_id
        FROM
            corresponding1
        WHERE
            corresponding1.id = color_id)
WHERE
    color_id IN (SELECT
            id
        FROM
            corresponding)

最终，我删除了重复项：

DELETE FROM colors WHERE id IN (SELECT id FROM corresponding);

摘要

这个例子也许不是最好的例子来说明我的问题，但是在这里我想避免克隆临时表并找到一种在IN表上使用多个TEMPORARY条件进行选择的方法。

Answer 1

尝试反过来思考。

您可以这样做：

UPDATE octopuses
        INNER JOIN
    (SELECT 
        *,
            (SELECT 
                    id
                FROM
                    colors
                WHERE
                    colors.name = (SELECT 
                            name
                        FROM
                            colors
                        WHERE
                            color_id = colors.id)
                LIMIT 1) AS first_color_id
    FROM
        octopuses
    HAVING color_id <> first_color_id) AS DUP ON dup.color_id = octopuses.color_id 
SET 
    octopuses.color_id = first_color_id
WHERE
    octopuses.color_id <> first_color_id;


CREATE TEMPORARY TABLE to_delete SELECT id FROM colors WHERE NOT EXISTS (
    SELECT id FROM octopuses WHERE color_id = colors.id
);

DELETE FROM colors WHERE id IN (SELECT id FROM to_delete);

所以您的问题的答案是：

每当需要克隆临时表时，请三思而后行，您会发现另一种方法，该方法不涉及两次重新打开临时表！

如何在TEMPORARY表上选择多个IN条件？

问题

问题

数据

示例

摘要

1 个答案: