Insert, update, delete operations in PHP - Step-by-Step Execution

Concept Flow - Insert, update, delete operations

Start

↓

Choose Operation

↓

Insert

↓

Execute SQL Query

↓

Check Success?

No→Show Error

Yes↓

Finish

This flow shows choosing an operation (insert, update, delete), running the SQL query, checking if it worked, then finishing.

Execution Sample

PHP

<?php
// Insert
$sql = "INSERT INTO users (name, age) VALUES ('Alice', 30)";
// Update
$sql = "UPDATE users SET age = 31 WHERE name = 'Alice'";
// Delete
$sql = "DELETE FROM users WHERE name = 'Alice'";
?>

This code shows SQL commands for inserting, updating, and deleting a user named Alice.

Execution Table

Step	Operation	SQL Query	Execution Result	Action Taken
1	Insert	INSERT INTO users (name, age) VALUES ('Alice', 30)	Success	User Alice added
2	Update	UPDATE users SET age = 31 WHERE name = 'Alice'	Success	User Alice age updated to 31
3	Delete	DELETE FROM users WHERE name = 'Alice'	Success	User Alice removed
4	Insert	INSERT INTO users (name, age) VALUES ('Alice', 30)	Fail	Error shown: Duplicate entry
5	Update	UPDATE users SET age = 31 WHERE name = 'Bob'	Fail	Error shown: User not found
6	Delete	DELETE FROM users WHERE name = 'Bob'	Fail	Error shown: User not found

💡 Execution stops after all operations tried or on error handling.

Variable Tracker

Variable	Start	After Insert	After Update	After Delete
users table	empty	[{'name':'Alice','age':30}]	[{'name':'Alice','age':31}]	empty

Key Moments - 3 Insights

Why does the update operation only change Alice's age and not add a new user?

Because the SQL UPDATE command changes existing rows matching the WHERE condition. If no row matches, nothing is added. See execution_table row 2 where update succeeds only if user exists.

What happens if we try to insert a user that already exists?

The insert fails due to duplicate entry (primary key or unique constraint). See execution_table row 4 where insert fails and error is shown.

Why does delete fail when trying to remove a user not in the table?

Because DELETE affects only rows matching the WHERE condition. If none match, no rows deleted and often an error or no change occurs. See execution_table row 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the SQL query used in step 2?

A UPDATE users SET age = 31 WHERE name = 'Alice'

B INSERT INTO users (name, age) VALUES ('Alice', 30)

C DELETE FROM users WHERE name = 'Alice'

D UPDATE users SET age = 31 WHERE name = 'Bob'

💡 Hint

Check the 'SQL Query' column in execution_table row 2.

At which step does the users table become empty again?

A After Update

B After Delete

C After Insert

D Start

💡 Hint

Look at variable_tracker row for 'users table' after each operation.

If we try to update a user named 'Bob' who does not exist, what happens?

A User Bob is added

B Update succeeds silently

C Update fails and error is shown

D User Alice is updated instead

💡 Hint

See execution_table row 5 for update operation on non-existing user.

Concept Snapshot

Insert, update, delete are SQL commands to add, change, or remove data.
Insert adds new rows.
Update changes existing rows matching a condition.
Delete removes rows matching a condition.
Always check if operation succeeded to handle errors.

Full Transcript

This visual execution shows how insert, update, and delete operations work in PHP with SQL. First, you choose the operation, then run the SQL query. Insert adds a new user named Alice. Update changes Alice's age to 31. Delete removes Alice from the table. If you try to insert Alice again, it fails due to duplicate. Updating or deleting a user not in the table also fails. Variables track the users table state after each operation. Key moments explain why update doesn't add new users, why insert can fail on duplicates, and why delete fails if user not found. The quiz tests understanding of SQL queries, table state changes, and error cases. Remember to always check if your database operation succeeded.