In this tutorial, we'll explore how to use SQL expressions for validation in Oracle APEX. SQL expressions are like smart rules that help you decide if the data entered in your application is correct. We'll go through the process step by step and provide examples to make it easy to understand. What is an SQL Expression for Validation? An SQL expression for validation is like a detective checking if something is true or false in your application. It's a way to define a condition that must be met for data to be considered valid. If the condition is true, the data is accepted; if it's false, you'll get an . Oracle APEX error message Creating an SQL Expression Validation Let's walk through the process of creating an SQL expression validation: Go to Page Designer: Open your Oracle APEX application and go to "Page Designer." Select Your Page Item: Choose the page item that you want to validate. In our example, we'll use . P2_JOB Add a Validation: In the properties of the selected page item, go to the "Validation" section and click on "Add." Choose Validation Type: Select "SQL Expression" as the validation type. This tells APEX that we're going to use an SQL expression to validate our data. Define the SQL Expression: In the "SQL Expression" field, enter your SQL code. Let's say we want to validate that the job is either 'MANAGER' or the department is located in 'CHICAGO'. Here's the SQL expression: :P2_JOB = 'MANAGER' OR
EXISTS (
    SELECT 1
    FROM dept
    WHERE deptno = :P2_DEPTNO
    AND loc = 'CHICAGO'
) This SQL expression checks if is 'MANAGER' or if the department specified by is located in 'CHICAGO'. If either condition is true, the data is valid. P2_JOB P2_DEPTNO Set Validation Attributes: You can further customize your validation by setting attributes like error message text, error message display location, and more. Save and Run: Save your validation, and now, when a user enters data in , it will be checked against your SQL expression. If it meets the conditions, it's valid; otherwise, an error message will be displayed. P2_JOB Additional Examples Example 1: Checking Age Limit Let's say you have a page item where users enter their age. You want to make sure they are older than 18. Here's the SQL expression: P3_AGE :P3_AGE > 18 This SQL expression checks if the age entered in is greater than 18. If it is, the data is valid. P3_AGE Example 2: Validating Email Format Suppose you have a page item where users enter their email addresses. You want to validate that the email follows a proper format. Here's the SQL expression: P4_EMAIL REGEXP_LIKE(:P4_EMAIL, '^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}$') This SQL expression uses a to check if the email address matches a valid format. regular expression Example 3: Ensuring Unique Usernames If you have a page item where users enter their usernames, you may want to ensure that the username is unique. Here's the SQL expression: P5_USERNAME NOT EXISTS (
    SELECT 1
    FROM users
    WHERE username = :P5_USERNAME
) This SQL expression checks if the username entered in doesn't already exist in the user’s table. P5_USERNAME Testing the SQL Expression Validation To test your SQL expression validation, simply run your APEX application and enter different values in the respective page items. The validation will check if the conditions are met and provide error messages when needed. Conclusion SQL expressions for validation in Oracle APEX are like detectives ensuring that your data is correct. In this tutorial, we learned how to create an SQL expression validation, define the SQL code, and customize its attributes.

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