MS SQL 2005 Auto Increment Error - php

Question

So, I have tried to create a table inside my database 'Test',
CREATE TABLE TestTbl(
id INT IDENTITY(1,1),
Agent_id VARCHAR(255) NOT NULL
)
After it was created, I tried to add 2 values for the agent via php, but the result is this:
id | Agent_id
0 8080
0 8081
It does not auto increment, even if I set 'id' as a Primary key, still the problem occurs, anyone knows how to solve this problem?
Here is my insert statement in php, nevermind the $conn, because it works, it is for my sql connection
if(isset($_POST['agentid'])){
$agent = $_POST['agentid'];
$query = "SELECT * FROM [Test].[dbo].[TestTbl] WHERE [Agent_id] = '$agent'";
$result = sqlsrv_query($conn,$query);
if(sqlsrv_has_rows($result) !=0){
echo "ID EXISTS";
}else{
$sql = "SET INDENTITY_INSERT TestTbl ON
INSERT INTO [Test].[dbo].[TestTbl]
([id],[Agent_id]) VALUES ('','$agent')
SET IDENTITY_INSERT TestTbl OFF";
echo "Added";
}}

Answer 1

Change this part
From
INSERT INTO [Test].[dbo].[TestTbl]
([id],[Agent_id]) VALUES ('','$agent')
To
INSERT INTO [Test].[dbo].[TestTbl]
([Agent_id]) VALUES ('$agent')
When it's auto increment, you don't' need to specify that in your INSERT statement.
Also do not SET IDENTITY_INSERT to OFF when you want to use auto increment feature of your table
SET IDENTITY_INSERT allows explicit values to be inserted into the identity column of a table.
Your complete query
if(isset($_POST['agentid'])){
$agent = $_POST['agentid'];
$query = "SELECT * FROM [Test].[dbo].[TestTbl] WHERE [Agent_id] = '$agent'";
$result = sqlsrv_query($conn,$query);
if(sqlsrv_has_rows($result) !=0){
echo "ID EXISTS";
}else{
$sql = "INSERT INTO [Test].[dbo].[TestTbl]
([Agent_id]) VALUES ('$agent')";
echo "Added";
}}