Practice PHP interview answers on equality, types, interfaces, database access and request validation with a duplicate-order case. These original practice questions connect a concept to a decision and a failure case. They are preparation exercises, not leaked employer questions. State your assumptions before proposing an implementation.
Why distinguish loose and strict comparison?
Loose comparison can coerce values, while strict comparison also considers type. Identify what the input actually is: a submitted string, a parsed number or an optional value. Do not depend on coercion to decide whether a customer ID is valid. Normalize intentionally at the boundary and test values such as an empty string, zero and a missing field according to the business rule.
What does an interface help communicate?
It describes a capability that an implementation supplies. An order service can depend on a payment interface rather than a particular transport client. Explain the actual boundary and failure contract, not just the keyword. An interface with every possible vendor option can be as difficult to use as the concrete class it replaced. Keep the abstraction tied to what the caller needs.
How do you validate data in an HTTP request?
Separate parsing, basic shape validation and business permission checks. The client may omit a field, send an unexpected type or reference a resource it may not access. Return a consistent response for invalid input and enforce the important constraints on the server. A typed internal method is useful, but it is not a complete policy for untrusted input entering through an endpoint.
What protects a database query from SQL injection?
Use parameterized queries so values remain data rather than being assembled into SQL instructions. Validation supports business rules but is not a substitute for safe query construction. Dynamic identifiers such as column names need an appropriate allowlist because they are not ordinary parameter values. Explain the difference and give the caller a limited supported set of sort options.
How do you prevent duplicate business operations?
A repeated HTTP request can arrive because of a client retry or timeout. Define a stable operation key and enforce the uniqueness or completion rule at the durable boundary. Checking an in-memory variable in one request is not enough across concurrent requests. Explain how the same key with different content is handled and how a caller can learn the outcome after a lost response.
Worked interview scenario
Original case: a checkout creates an order, but the client does not receive the response and retries. The handler inserts another row because it has no durable duplicate rule. Begin by defining whether the two requests represent the same logical order and which stable key identifies it.
Store the key with the order under an appropriate uniqueness constraint and transactional design. On a repeat, return the existing outcome where the request matches. Reject or investigate conflicting content under the same key. Test a lost response, simultaneous retries and a failed operation that may be retried. Distinguish preventing duplicate rows from coordinating a separate payment provider's side effects.
Practice exercise
Describe the order endpoint's input, validation, permission and persistence boundaries. Write a small table of strict-comparison cases before predicting their results. Then explain why query parameters do not automatically solve dynamic column-name selection and propose a limited sort-field contract.
Review your explanation
Use Cluegent during practice to challenge your own draft. Ask for a follow-up about the scenario's weakest assumption, answer it without suggestions, then check your reasoning against the official reference. Review current plans before subscribing. Follow the employer's tool policy in the actual interview.
Sources checked
These official references support the guide. Product details and technical documentation can change; check the linked source for current information.
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Frequently asked questions
Is strict comparison always enough for validation?
No. It makes type comparison explicit, but you still need parsing and business constraints appropriate to the field.
Can request-local state prevent duplicate orders?
It cannot reliably coordinate separate concurrent requests. Enforce the duplicate rule at the durable business boundary.