How to select with multiple IN conditions on TEMPORARY table? - mysql

Question

The Problem
I would like to sanitize a messy database and replace references to duplicate entries. In this custom made (mine is far more complex) example I have two tables:
Octopuses
Colors
We know that:
An octopus has a color.
Table colors contain duplicates
Some octopuses may have the same color as other octopuses, but different color_id.
The way I solved this problem involves TEMPORARY tables. To avoid the error:
Can't Reopen Table 'duplicates'
I simply duplicate my TEMPORARY table many times:
CREATE TEMPORARY TABLE duplicates1 SELECT * FROM duplicates;
CREATE TEMPORARY TABLE duplicates2 SELECT * FROM duplicates;
The Question
I would like to avoid to clone TEMPORARY tables.
The Data
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`));
With some colors with duplicate:
INSERT INTO colors (name) VALUES
('cream'), ('sepia'), ('daffodil'), ('lipstick'),
('lipstick'), ('garnet'), ('flamingo'), ('navy'),
('chartreuse'), ('garnet'), ('flamingo'), ('juniper'),
('flint'), ('flint'), ('charcoal'), ('garnet');
And some octopuses:
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);
The Example
To solve the problem I first create the list of duplicates:
CREATE TEMPORARY TABLE duplicates SELECT
*, COUNT(*) AS count
FROM
colors
GROUP BY name
HAVING count > 1;
Here it is:
mysql> select * FROM duplicates;
+----+----------+-------+
| id | name | count |
+----+----------+-------+
| 4 | lipstick | 2 |
| 6 | garnet | 3 |
| 7 | flamingo | 2 |
| 13 | flint | 2 |
+----+----------+-------+
Then I would like to create a corresponding table where I have the id of a duplicate and the id to be replaced with:
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;
Here the content:
mysql> SELECT * FROM corresponding;
+----+----------+----------+
| id | name | first_id |
+----+----------+----------+
| 11 | flamingo | 7 |
| 14 | flint | 13 |
| 10 | garnet | 6 |
| 16 | garnet | 6 |
| 5 | lipstick | 4 |
+----+----------+----------+
Then I simply update the octopuses table:
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)
Eventually I remove the duplicates:
DELETE FROM colors WHERE id IN (SELECT id FROM corresponding);
The Summary
This example is perhaps not the best to illustrate my issue, but here I would like to avoid to clone temporary tables and find a way to select with multiple IN conditions on TEMPORARY tables.

Answer 1

Try to think the other way around.
You could do:
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);
So the answer to your question is:
Whenever you need to clone a temporary table, think twice and you will find another way that do no involve reopening temporary table twice!