Скачать или смотреть How to Write a CHECK Constraint in MySQL for Specific Column Patterns

Discover how to create a `CHECK` constraint in MySQL that ensures a column follows a specific string format, like starting with 'CLS' followed by a 5-digit number.
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This video is based on the question https://stackoverflow.com/q/64642001/ asked by the user 'Sakshi Ray' ( https://stackoverflow.com/u/14383848/ ) and on the answer https://stackoverflow.com/a/64642517/ provided by the user 'manuel antunes' ( https://stackoverflow.com/u/11097113/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Write a CHECK Constraint in MySQL for Specific Column Patterns

When it comes to database design, ensuring the integrity of your data is vital. One effective way to ensure the carefully crafted data model adheres to specific rules is by using constraints. In this guide, we'll explore how to write a CHECK constraint in MySQL for a column that requires values to start with CLS followed by a five-digit number.

The Problem: Defining Your Data Constraints

Imagine you have a database column, class_id, that should only store values in a specific format. For instance, you want to allow values like:

CL100987

CLS45678

These values should start with the letters CLS and be followed by a five-digit number. To enforce this rule, we can use a CHECK constraint in MySQL.

The Solution: Using Regular Expressions

MySQL allows you to enforce constraints using regular expressions with the REGEXP_LIKE function. Let’s break down how to create this constraint step by step:

1. Understanding REGEXP_LIKE

REGEXP_LIKE is a function that checks whether a string matches a specified regular expression pattern. For our case, we want to assert that the string meets two conditions:

It starts with CLS

It is followed by exactly five digits

2. Writing the CHECK Constraint

To implement this in MySQL, our CHECK constraint would look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Regular Expression

^: Asserts that we are at the start of the string.

CLS: Specifies that the string must start with 'CLS'.

[0-9]{5}: Ensures that there are exactly five digits following 'CLS'.

$: Asserts the end of the string.

3. Taking Database Variations into Account

Keep in mind that implementation details can vary between different database management systems (DBMS). While this example is given in the context of MySQL, other systems may have different syntax or capabilities regarding regular expressions. Always consult your specific DBMS documentation for precise usage.

An Example in Action

Here’s an example of how you might create a table with this constraint:

[[See Video to Reveal this Text or Code Snippet]]

With this table definition, if someone tries to insert CLS1234 or ABCD56789 into the class_id column, the database will throw an error, enforcing the rule we defined.

Conclusion

In summary, using a CHECK constraint with regular expressions in MySQL is an effective way to ensure that the data you store in your database meets specific formatting requirements. By following the steps outlined above, you can maintain data integrity and only allow valid entries in your class_id column. Happy coding!