How do I set a max value for a column int using SQL C#

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Hello, So I am having a library management system that let students add books to their table I want to set the maximum books that student can add is 5???

What I have tried:

So I have tried to give each student added a max books column that has int 0 when a student adds a book the int will equal 1 ........ to a 5 when it will be 5 it will return a message.. the question is how do I set the max value 5?

Posted 16-May-21 0:19am

Omar Dakelbab

Updated 16-May-21 4:49am

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Richard MacCutchan 16-May-21 7:08am

How are you storing the books in the student's database entry?

Omar Dakelbab 16-May-21 7:09am

I created a table that stores all added books by students inside that table i have book_ID, student_ID and the dateTime

Omar Dakelbab 16-May-21 7:12am

So when student add book column(maxBooks) = maxBooks + 1; when maxbooks = 5 return a message

3 solutions

Solution 1

In WPF you can use ValidationRule, see example here:
How to set Minvalue and Max Value for a testbox in wpf[^]

Or use this custom NumericUpDown control: Creating a NumericUpDown control from scratch[^]

If you want to do it in SQL use a Constraint, see: SQL constraint minvalue / maxvalue? - Stack Overflow[^]

Posted 16-May-21 0:28am

RickZeeland

Updated 16-May-21 1:06am

v3

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Omar Dakelbab 16-May-21 6:54am

thanks for the reply but i want to set the max value in the SQL table

Solution 2

Controlling the amount of rows in the database is a bit more tricky because you cannot do it using a simple constraint. Constraints work only on row level, for example like NOT NULL constraint.

However, using T-SQL programming and a trigger you can enforce the business logic you want, even for a set of rows. For an example you might want to read Control maximum number of rows in a table[^]

Posted 16-May-21 4:31am

Wendelius

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Richard MacCutchan · Accepted Answer · 2021-05-16T04:49:00

Solution 3

SQL COUNT(), AVG() and SUM() Functions[^]. So something like:

SQL

SELECT COUNT(Books) FROM BookTable WHERE student_Id = this student's id;

If the returned value is 5 then reject the request.

Posted 16-May-21 4:49am

Richard MacCutchan

Comments

Omar Dakelbab 16-May-21 14:02pm

Thanks for the reply