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These are used to define and refine the schema of the database. Create statements and a few others like alter, drop, and truncate are examples of SQL used as a data definition language. I'll refresh my view and my table was created. I have created a database with these tables : CREATE TABLE kurs.personal (personalid INT IDENTITY(1,1), chefidINTNULL, lonekatidINTNOT NULL, fornamn CHAR(20) NOT NULL. When that command is complete I'll send it to the database. FavoriteDish is a foreign key in this table, and once again, depending on the DBMS you're using, the way you set up and enforce this relationship will be different. Here I've indicated that this field references the DishID from the Dishes table. I'll add Birthday and then I'll add FavoriteDish. This is a business requirement, and we'll satisfy it by letting the database's constraints prevent us from entering a record that doesn't fit our business requirement. We'll set Phone to NOT NULL because we need some way to contact our customers. If we use another connection for the alter command that means if metadata lock is active then the alter statement will. For example, we can add columns into the specified table then we can easily add new columns with the data type.
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I'll continue by adding more of the fields from my notes. SQLite provides an add column functionality to the user, in which we can change the structure of existing tables. For a great resource about valid name requirements, check out Patrick McKenzie's blog post called Falsehoods Programmers Believe About Names. In some cultures people can have single names and in others you'll need to accommodate more than just a FirstName and a LastName. Depending on where the people in your database are from you may have different requirements for a valid name. We don't want to put in a customer with no name. And we'll set the constraint that they not be null. FirstName and LastName will be of variable lengths up to 200 characters. Then I'll go through the other fields and write down what they need to be. In the system I'm using I need to add a line like this. There are different ways to indicate that a field is a primary key depending on the system you're using. Every time we add a new customer that new row will get a unique number, the next one in the sequence. So it's not null and it'll auto-increment. Because it's the primary key it can't contain a null value. For my notes I know that the data it will hold will be an integer, up to six digits. First, I'll add a field called CustomerID. Then within a set of parentheses we'll add information about the columns.
SQLITESTUDIO REMOVE TABLE CONSTRAINT HOW TO
In SQL we'll start writing a description of how to create a table and we'll give it the name Customers.
![sqlitestudio remove table constraint sqlitestudio remove table constraint](http://www.cheat-sheets.org/own/sqlite/imgs/table-constraint.gif)
Once I have a database I can work with I'll use the CREATE keyword in SQL along with parameters for our fields to tell the database what we want a table to look like.