This is an example of a SQL drop constraint in action. It’s a very useful feature for developers. It gives them a means to prevent database changes from changing your schema. Let’s say you have a table with a field called “credential_type” where the value is either “user” or “admin”.
When you add a column to a table in a database, it is very easy to forget to remove that column. The easiest way to remove a column in MySQL is to use a drop constraint. In this example we’ve set the column to be user.
Drop constraints are used to limit what can be written on a table. The goal in a drop constraint is to limit the amount of terms to which a table can be written. The drop constraint also allows you to limit the amount of fields to which a table can be written. It can be a lot of work, but one of the best parts is the ability to read and write back those fields and get a response back to the table owner.
This is the third of the three drop constraints in the MySQL database, based on the fact that there are no real constraints. They can be set to allow the user to only have the field value in the table, rather than the column name.
As opposed to SQL, which is very easy to write, it’s much harder to read and write.
And you could also limit the number of rows in the table to let the user only have a subset of the columns they want to see. For example, you could have a drop constraint that only allow users to see the first 10 columns in the table. There are only a few real problems here. One, it will prevent the user from seeing any rows, which is not a great deal. Two, it will allow the user to only see a subset of the columns, causing more work.
Let’s say you want to limit a user to see the first 10 columns of the table. You start by writing a constraint that says: “Only allow users to see the first 10 columns.
The problem with this constraint is that it will allow the user to see the entire table. It doesn’t prevent them from seeing the first 10 columns.
It would be nice if it had a simple way to prevent that. Locking it all on one column would eliminate the potential for SQL injection. The only way I could actually do that was by setting a limit to the number of columns. I never thought of doing that.
This is so, so simple. I could have used a more powerful constraint, like CONSTRAINT {PERSISTENCE} LIMIT 10. This would have required some changes to the code, but could be easily fixed by adding a new column. I could have also used a WHERE clause. This would have required some changes to the code, but would be easy enough to fix by adding a new column.
