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Write-a-PLSQL-Trigger-to-insert-employee-records-into-a-table-when-deleted.html
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<h1 class="mb-4" style="font-weight: 800;"> Write a PL/SQL Trigger to Insert Employee Records Into a Table When Deleted</h1>
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<span class="d-inline-block mt-1">By DarkSoul</span>
<span> - August 10, 2024</span>
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<p>An HR system has an Employee table that holds a row for each employee within the company. Each record in the table has a employee id, employee name and manager column, that holds the id for the employee's manager. Write a trigger so that when an employee record is deleted, the record details need to be inserted into an table called Employee_archive along with the deleted date.</p>
<p>Table: EMPLOYEE</p>
<table class="table table-hover table-dark table-striped mt-4 mb-4" style="max-width: 400px;">
<thead>
<tr>
<th>COLUMN</th>
<th>DATATYPE</th>
<th>CONS.</th>
</tr>
</thead>
<tbody>
<tr>
<td>EMPID</td>
<td>NUMBER</td>
<td>PK</td>
</tr>
<tr>
<td>EMP_NAME</td>
<td>VARCHAR2(25)</td>
<td></td>
</tr>
<tr>
<td>MANAGERID</td>
<td>NUMBER</td>
<td></td>
</tr>
</tbody>
</table>
<p>Table: EMPLOYEE_ARCHIVE</p>
<table class="table table-hover table-dark table-striped mt-4 mb-4" style="max-width: 400px;">
<thead>
<tr>
<th>COLUMN</th>
<th>DATATYPE</th>
<th>CONS.</th>
</tr>
</thead>
<tbody>
<tr>
<td>EMPID</td>
<td>NUMBER</td>
<td>PK</td>
</tr>
<tr>
<td>EMP_NAME</td>
<td>VARCHAR2(25)</td>
<td></td>
</tr>
<tr>
<td>MANAGERID</td>
<td>NUMBER</td>
<td></td>
</tr>
<tr>
<td>DELETED_DATE</td>
<td>DATE</td>
<td></td>
</tr>
</tbody>
</table>
<strong>(Hint: Data is case sensitive. Use '/' to terminate the PLSQL block)</strong>
<div class="col-md-12 mb-4" style="display: flex;">
<textarea disabled id="plsql">
CREATE TRIGGER archive
BEFORE DELETE ON Employee
FOR EACH ROW
BEGIN
INSERT INTO Employee_archive VALUES(:old.EMPID, old. EMPNAME, old.MANAGERID, SYSDATE);
END;
/
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<h2>
Step-by-Step Guide to Creating the Trigger
</h2>
<p><b>Introduction to Triggers:</b><br>
First, understand that a trigger is a special kind of stored procedure that automatically executes when a specific event occurs in the database.
In this guide, we’ll focus on creating a trigger that helps archive employee records automatically when they are deleted from the main table.</p>
<p><b>Choosing the Event:</b><br>
In this case, we want the trigger to execute before an employee record is deleted from the Employee table. This allows us to capture and save the record in an archive table before it’s removed.</p>
<p><b>Writing the Trigger Code:</b><br>
Let's break down the trigger code step by step.</p>
<p><b>Trigger Declaration:</b><br>
We start by declaring the trigger with a name. Here, it's called <b>archive</b>:
<pre><code class="language-sql">CREATE TRIGGER archive</code></pre>
This line tells the database we're creating a new trigger called <b>archive</b>.</p>
<p><b>Specifying the Timing and Event:</b><br>
Next, we specify when this trigger should run and on which table. We want it to run before a row is deleted from the Employee table:
<pre><code class="language-sql">BEFORE DELETE ON Employee</code></pre>
This means the trigger will activate right before a deletion occurs.</p>
<p><b>Defining the Scope:</b><br>
We need the trigger to execute for each row that's deleted, so we include:
<pre><code class="language-sql">FOR EACH ROW</code></pre>
This ensures the trigger processes each row individually.</p>
<p><b>Writing the Trigger Body:</b><br>
Now, we define what the trigger should do. In this case, we want to insert the deleted employee record into an archive table:
<pre><code class="language-sql">
BEGIN
INSERT INTO Employee_archive VALUES(:old.EMPID, :old.EMPNAME, :old.MANAGERID, SYSDATE);
END;
/
</code></pre>
<b>BEGIN</b> and <b>END</b> are used to enclose the actions the trigger will perform.<br>
The <b>INSERT INTO</b> statement copies data from the deleted record (referenced by <b>:old</b>) into the `Employee_archive` table, along with the current date and time (using <b>SYSDATE</b>).
</p>
<p><b>Conclusion:</b><br>
With this trigger in place, every time an employee record is deleted from the Employee table, it is automatically archived in the `Employee_archive` table. This ensures you have a backup of important data before it gets permanently removed.
</p>
<div class="pt-5">
<p>Categories: <a href="category-pl-sql.html">PL/SQL Hands-on</a> Tags: <a href="#">#Write a PL/SQL Trigger to insert employee records into a table when deleted</a>, <a href="#">#PL/SQL</a></p>
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