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Mysql error 1452 - Cannot add or update a child row: a foreign key constraint fails
... having a bit of a strange problem. I'm trying to add a foreign key to one table that references another, but it is failing for some reason. With my limited knowledge of MySQL, the only thing that could possibly be suspect is that there is a foreign key on a different table referencing the one I am ...
MySQL: Fastest way to count number of rows
...eyword after SELECT:
SELECT SQL_CALC_FOUND_ROWS [needed fields or *] FROM table LIMIT 20 OFFSET 0;
After you have selected needed rows, you can get the count with this single query:
SELECT FOUND_ROWS();
FOUND_ROWS() has to be called immediately after the data selecting query.
In conclusion,...
MVC (Laravel) where to add logic
...E.g., whenever someone publishes a post I also want to save something to a table for analytics. Maybe not the best example but in general there's a lot of this "grouped" functionality.
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How do you effectively model inheritance in a database?
...database. Which you choose depends on your needs. Here are a few options:
Table-Per-Type (TPT)
Each class has its own table. The base class has all the base class elements in it, and each class which derives from it has its own table, with a primary key which is also a foreign key to the base clas...
How to use php serialize() and unserialize()
...p script ready to store/send it somewhere. You have the option to create a table that exactly matches the expected data, but this is tedious you are essentially doubling your work load because you have to write code that matches too, plus changes in database need changes in code or vice versa. When ...
Select n random rows from SQL Server table
I've got a SQL Server table with about 50,000 rows in it. I want to select about 5,000 of those rows at random. I've thought of a complicated way, creating a temp table with a "random number" column, copying my table into that, looping through the temp table and updating each row with RAND() , and ...
Deleting all records in a database table
How do I delete all records in one of my database tables in a Ruby on Rails app?
7 Answers
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Best design for a changelog / auditing database table? [closed]
I need to create a database table to store different change log/auditing
(when something was added, deleted, modified, etc). I don't need to store particularly detailed info, so I was thinking something along the lines of:
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When to use EntityManager.find() vs EntityManager.getReference() with JPA
...tabase entity and then pass the returned object to be persisted in another table.
5 Answers
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What GRANT USAGE ON SCHEMA exactly do?
...chema within. Similiarly, GRANTing on a schema doesn't grant rights on the tables within.
If you have rights to SELECT from a table, but not the right to see it in the schema that contains it then you can't access the table.
The rights tests are done in order:
Do you have `USAGE` on the schema?...