PDO and MySQLi both let PHP talk to MySQL safely when you use their APIs correctly. The difference is their scope and style, not a simple ranking of good and bad. PDO supports multiple database drivers through a common interface. MySQLi focuses on MySQL and exposes its features directly. The existing course uses PDO as its main database path; this MySQLi material is an optional track for reading projects that use it or building a MySQL-specific application. This reference compares connections, placeholders, fetching, errors, and transactions so you can choose intentionally rather than rewriting working code for a slogan.
Understand what portability really means
PDO can connect to MySQL, PostgreSQL, SQLite, and other databases when the appropriate driver is installed. Its prepare(), execute(), and fetch() patterns remain recognizable across drivers. That does not make SQL syntax, column types, isolation rules, or schema migrations portable automatically. A MySQL AUTO_INCREMENT definition still needs adaptation for another engine. MySQLi supports MySQL only, with object-oriented and procedural APIs. Pick one style consistently inside a project. Both extensions require the relevant PHP installation support, and a successful CLI extension check does not prove the web process uses the same configuration. For a course or reusable data layer, PDO's shared shape can simplify teaching; for a MySQL-specific codebase, MySQLi may fit existing conventions and tools.
Compare connection and character-set handling
PDO uses a DSN such as mysql:host=...;dbname=...;charset=utf8mb4 plus options. MySQLi constructs a connection with separate host, user, password, and database arguments, then uses set_charset('utf8mb4'). Explicit character-set configuration matters for correct text storage and comparisons. Keep credentials outside public files and create a connection under a clear request-lifetime policy. Configure errors explicitly instead of relying on defaults that changed across PHP versions. Remote production connections may need verified TLS according to the driver and hosting environment. A connection API does not choose a least-privilege account for you. Whether you use PDO or MySQLi, grant only the application's required operations and separate migration privileges from ordinary request privileges.
Compare prepared-statement values
PDO supports question-mark placeholders and named placeholders, although driver details and emulated prepares require attention. MySQLi uses positional question marks in its traditional prepare()/bind_param()/execute() flow. bind_param() includes type letters and binds variables by reference, so values must be variables rather than arbitrary expressions. The letter i denotes an integer, d a floating value, s a string, and b binary data with its related handling. An SQL decimal price is often bound as a validated decimal string to avoid premature binary-floating conversion. Both APIs keep parameter values separate from statement structure. Neither can bind a table name or ORDER BY identifier as a value; use an allowlist for dynamic identifiers. Prepared statements also do not replace authorization.
Compare reading and writing results
PDO can return associative arrays through FETCH_ASSOC and provides fetch(), fetchAll(), and fetchColumn(). MySQLi result objects provide fetch_assoc() for ordinary queries. Prepared-statement get_result() depends on mysqlnd support, so a portable MySQLi example can use bind_result() and fetch() instead. Check which API your hosting environment supports before copying a result-fetching shortcut. For updates and deletes, affected-row behavior can distinguish changed rows from matched rows depending on connection options and database semantics. Do not treat zero affected rows as proof a record never existed without considering unchanged values. Both APIs support retrieving generated insert IDs, but use the ID on the same connection and understand multi-row behavior. Large result sets need a deliberate memory and buffering policy.
Use transactions and errors consistently
Both APIs can start, commit, and roll back transactions, subject to the database engine and table support. PDO offers beginTransaction(), commit(), and rollBack(); MySQLi offers begin_transaction(), commit(), and rollback(). Database DDL can cause implicit commits in MySQL, so a transaction is not a universal undo wrapper around CREATE TABLE. Use exceptions or checked error paths consistently and preserve the original failure when cleanup also fails. A valid input can still conflict with a unique constraint under concurrency. Return a useful conflict response for expected cases and log unexpected failures privately. Avoid exposing SQL, server names, or credentials through raw exception messages. Transaction retry needs a business-level policy; blindly repeating a successful external side effect can duplicate work.
Choose according to the project
Keep an existing well-maintained API if it meets your database and security requirements. Moving between PDO and MySQLi changes statement binding, fetch behavior, connection setup, and error handling; it needs tests of real behavior rather than a mechanical search-and-replace. Choose PDO when its common interface and existing course examples help you, and MySQLi when a MySQL-specific project intentionally uses its capabilities. Do not mix both connections inside one transaction and expect them to share state. They are separate sessions even when they reach the same database. Wrap connection creation in a small factory and keep SQL close to the code that needs it. An abstraction should simplify repeated policy, not hide every meaningful database distinction.
Practice task and worked solution
Compare a small existing PDO repository method with a proposed MySQLi implementation. The solution must preserve missing-row behavior, strict input validation, character-set setup, private error handling, and prepared values. Use bind_result() if mysqlnd is not guaranteed. Check a valid ID, missing ID, malicious text rejected by the input validator, and a connection failure. Then compare an update that assigns the existing value to avoid misinterpreting zero changed rows. Document whether migration offers a concrete benefit. For this course, keep PDO as the main path and treat the MySQLi implementation as optional practice.
Continue learning
Continue from PDO and MySQL, CRUD, and security.
The PHP database extension comparison describes API scope and supported features.
MySQLi vs. PDO Examples
Each example shows the code, the output it produces and what each part does.
The same read in two APIs
Both examples assume valid configured connections to the same MySQL schema. They request one product by a validated integer ID and bind the value separately.
If product 12 is Pen, output is PDO: Pen then MySQLi: Pen. If it does not exist, both paths report not found. Database rows and connection setup are environment-dependent, and this demonstration does not create live connections itself.
<?php
$id = 12;
// PDO connection in $pdo:
$pdoStatement = $pdo->prepare('SELECT name FROM products WHERE id = ?');
$pdoStatement->execute([$id]);
$pdoName = $pdoStatement->fetchColumn();
// MySQLi connection in $mysqli:
$mysqliStatement = $mysqli->prepare('SELECT name FROM products WHERE id = ?');
$mysqliStatement->bind_param('i', $id);
$mysqliStatement->execute();
$mysqliStatement->bind_result($mysqliName);
$found = $mysqliStatement->fetch();
echo $pdoName === false ? 'PDO: not found' : 'PDO: ' . $pdoName;
echo PHP_EOL;
echo $found ? 'MySQLi: ' . $mysqliName : 'MySQLi: not found';With product 12 named Pen:
PDO: Pen
MySQLi: PenMySQLi vs. PDO FAQ
Is one API automatically secure?
No. Both mysqli and PDO are secure when you bind values with prepared statements, and both are vulnerable when you build SQL from strings. Safe binding, validation, authorization, and configuration such as a restricted database account matter far more than the choice of API.
Does PDO make all SQL portable?
No. PDO gives one PHP interface to many databases, but the SQL you send still uses that database's dialect. Differences remain in functions, LIMIT syntax, data types and how generated keys are returned, so switching databases still means reviewing queries.
Can a placeholder name a table?
No. Placeholders represent values, not identifiers such as table or column names, so SELECT * FROM ? doesn't work. Choose identifiers from a fixed allowlist in your code, for example mapping a sort option to a known column name.
Can both connections share one transaction?
No. A mysqli connection and a PDO connection are separate database sessions, each with its own transactions. Changes made through one aren't part of a transaction started on the other, so use a single connection for work that must commit or roll back together.
MySQLi vs. PDO Exercises
Answer each one and check it instantly. If you get stuck, open the hint before the answer.
A project needs PostgreSQL and MySQL drivers through one access shape. Which fits?
MySQLi vs. PDO Quiz
2 questions to check what you learned.
Which statement describes PDO portability accurately?
- Every schema becomes portable unchanged
- Its access API is shared, but SQL dialect differences remain
- PDO supports only MySQL
- PDO removes database permissions
Which placeholder is used by traditional MySQLi prepare?
- A PDO-style named parameter such as :email
- A PostgreSQL-style numbered parameter such as $1
- A positional question mark
- A quoted question mark inside a SQL string literal