I'm trying to find all rows in table 'wpi9_pc_products' that have less than 3 entries in table 'wpi9_term_relationships', so that I can delete them from both.
Before shooting from the hip, I want to ensure I'm pulling the right rows for deletion, using this query:
SELECT * FROM `wpi9_pc_products` INNER JOIN wpi9_term_relationships ON
wpi9_pc_products.id_product=wpi9_term_relationships.object_id GROUP BY
wpi9_term_relationships.object_id HAVING COUNT(*) < 3
However, I'm stuck here trying to figure out the correct way to join the two tables conditionally based on the count.
My SQL is very, very rusty, so any help would be greatly appreciated!
If I am following correctly, you have a parent/child relationship between the products and the relationships table. I would recommend setting up a foreign key constraint on the child table, that references the parent table, like so:
alter table wpi9_term_relationships
add constraint fk_product_id
foreign key (object_id)
references wpi9_pc_products(id_product)
on delete cascade;
Then, you can simply delete the records from the parent table; the on delete cascade clause ensures that the children records will be automatically deleted:
delete p
from wpi9_pc_products p
where (select count(*) from wpi9_term_relationships r where r.object_id = p.id_product) < 3
Related
table 1 is called (athlete) and table2 is called (training_session.id) the primary key to table 1 is ID, and the table 2 has the primary key Athelete_id
I want to delete a person from my database by using his name, which I've called "Pet". However, he is also connected to another table which stores his training session. So (ID 1) on table 1 is connected to table 2 (athlete id1)
I struggle a lot, I try using INNER JOIN.
DELETE athlete,training_session FROM athlete
INNER JOIN
training_session ON training_session.id = athlete.name
WHERE
athlete.name = "Pet;
I have something wrong with my syntax, is it correct to use Inner Join or have I misunderstood
You should have set up foreign key constraints with Cascade deletions to simplify the logic and all you would have needed than was to delete from athlete. So I would suggest you add it.
For more info you can take a look at:
http://www.mysqltutorial.org/mysql-on-delete-cascade/
I do not understand MySQL delete when I need to delete data in a table with data from another table that depend on it.
For example if I want to delete a data in table 'factory', all data at table 'room' that depends on data at table 'factory is also deleted'.
Fac_ID is the primary key in 'factory' and foreign key in 'room'
below is my SQL code.
DELETE * FROM factory
LEFT JOIN room ON room.Fac_ID = factory.Fac_ID
WHERE factory.Fac_ID = :Fac_ID
Can any one help me?
I think you need a separate delete for this.
First is to delete foreign data
delete from room where Fac_ID = :Fac_ID
Then delete primary data
delete from factory where Fac_ID = :Fac_ID
Unless your table design is ON DELETE CASCADE (supported only in INNODB), you only need to delete the primary data
There is a small mistake in your query because of which I think you are facing problem.
As per my understanding you have some records in Main table and some records in refrenced table. There are some case for which main table has some id but there is not entry in refrence table for that id. And for handling that case you applied left join.
But in your query you wrote reference table on left so basically it is taking all of the record from reference table which is kind of inner join in this case.
So for correcting this you need to interchange the key id pass in your query or you may use right join to select all records from main table.
DELETE * FROM factory
LEFT JOIN room ON factory.Fac_ID = room.Fac_ID --- here you applied left join
WHERE factory.Fac_ID = :Fac_ID
MySQL allows you to delete rows from multiple tables at the same time. The syntax is:
DELETE f, r
FROM factory f LEFT JOIN
room r
ON r.Fac_ID = f.Fac_ID
WHERE f.Fac_ID = :Fac_ID;
However, this is better set up as a cascading delete foreign key relationship between the two tables.
For this error message, is there a way for mysqlimport to output the specific row that fails the constraint? It's good for debugging. Otherwise, I don't know which row has this problem.
mysqlimport: Error: 1452, Cannot add or update a child row: a foreign key constraint fails (`bwordDS`.`Category_Term`, CONSTRAINT `FK_qn1crq26sr0hqm5q2p7nfvdu1` FOREIGN KEY (`categories_id`) REFERENCES `Category` (`id`)), when using table: Category_Term
First check if Category table exist where you are trying to import this data.
if Category table exists then need to check that all category_id in this table should exist in Category table as id.
Better option is to import first category table and then this table.
In generic first all parent tables data should import then child tables.
A dirty way is as per below which is not recommended-
set foreign_key_checks=0;
import data here;
set foreign_key_checks=1;
Just to know which row is creating problem-
Below query will provide you problematic rows.
SELECT a.category_id FROM Category_Term a
LEFT JOIN Category b ON a.category_id=b.id
WHERE b.id IS NULL;
Note: Assuming category_id in category_term and id in category tables will be indexed.
I used the sample query provided by #Zafar, but I added DISTINCT to SELECT as well:
SELECT DISTINCT countries.city_id
FROM countries
LEFT JOIN cities ON countries.city_id=city.id
WHERE city.id IS NULL;
I want to create a unique combokey on Site and ASIN and remove duplicates while creating
so far I have
ALTER TABLE Products ADD UNIQUE (Site,ASIN)
I figure there needs to be an "On Duplicate" but I cant find the right thing to do within http://dev.mysql.com/doc/refman/5.0/en/alter-table.html .. does anyone have a suggestion?
I don't think there is such a thing as ON DUPLICATE when adding a UNIQUE KEY. So you need to find a workaround. Here is a suggestion:
1- Identify the duplicate rows and store the values in a temp table.
CREATE TEMPORARY TABLE Duplicates
(SELECT
Site, ASIN
FROM
Products
GROUP BY
Site, ASIN
HAVING
COUNT(*) > 1
);
2- join the temp table with the original table and delete the duplicate rows that you don't need anymore. (from the comments I think you want to remove the ones with SKU IS NULL)
DELETE p
FROM
Products AS p
INNER JOIN
Duplicates AS d
ON
d.Site = p.Site and d.ASIN = p.ASIN
WHERE
p.SKU IS NULL;
3- create your unique key:
ALTER TABLE Products ADD UNIQUE KEY (Site, ASIN);
Here is a fiddle I created.
There are 2 tables, spawnlist and npc, and I need to delete data from spawnlsit.
npc_templateid = n.idTemplate is the only thing that "connect" the tables.
I have tried this script but it doesn't work.
I have tried this:
DELETE s FROM spawnlist s
INNER JOIN npc n ON s.npc_templateid = n.idTemplate
WHERE (n.type = "monster");
Add .* to s in your first line.
Try:
DELETE s.* FROM spawnlist s
INNER JOIN npc n ON s.npc_templateid = n.idTemplate
WHERE (n.type = "monster");
If the database is InnoDB then it might be a better idea to use foreign keys and cascade on delete, this would do what you want and also result in no redundant data being stored.
For this example however I don't think you need the first s:
DELETE s
FROM spawnlist AS s
INNER JOIN npc AS n ON s.npc_templateid = n.idTemplate
WHERE n.type = "monster";
It might be a better idea to select the rows before deleting so you are sure your deleting what you wish to:
SELECT * FROM spawnlist
INNER JOIN npc ON spawnlist.npc_templateid = npc.idTemplate
WHERE npc.type = "monster";
You can also check the MySQL delete syntax here: http://dev.mysql.com/doc/refman/5.0/en/delete.html
if the database is InnoDB you dont need to do joins in deletion. only
DELETE FROM spawnlist WHERE spawnlist.type = "monster";
can be used to delete the all the records that linked with foreign keys in other tables, to do that you have to first linked your tables in design time.
CREATE TABLE IF NOT EXIST spawnlist (
npc_templateid VARCHAR(20) NOT NULL PRIMARY KEY
)ENGINE=InnoDB;
CREATE TABLE IF NOT EXIST npc (
idTemplate VARCHAR(20) NOT NULL,
FOREIGN KEY (idTemplate) REFERENCES spawnlist(npc_templateid) ON DELETE CASCADE
)ENGINE=InnoDB;
if you uses MyISAM you can delete records joining like this
DELETE a,b
FROM `spawnlist` a
JOIN `npc` b
ON a.`npc_templateid` = b.`idTemplate`
WHERE a.`type` = 'monster';
in first line i have initialized the two temp tables for delet the record,
in second line i have assigned the existance table to both a and b but here i have linked both tables together with join keyword,
and i have matched the primary and foreign key for both tables that make link,
in last line i have filtered the record by field to delete.