PHP & MySQL · Lesson 6 of 11

SELECT

Read only the columns and rows an application needs.

Lesson

SELECT retrieves rows. Specify columns rather than using * in application queries, and add a deterministic ORDER BY when order matters. Paginate large result sets instead of loading an unbounded table into memory. The example selects a small set of public profile fields in a stable order. Further guidance Use migrations to version schema changes, constraints to protect relationships, and prepared statements for every dynamic value. Scope writes with a precise condition, check affected rows, and use transactions when multiple statements must succeed together. Store credentials outside source control. Practice task: Create a fresh example for SELECT. Predict the result before running it, then change one input and explain why the result changes. Test a normal case and one boundary or invalid case where it applies. Compare your output with the example and note one rule you would use in a real project.

Code examples

SELECT

SQL

SELECT id, display_name
FROM profiles
ORDER BY display_name ASC
LIMIT 20;

Expected output

At most 20 profile names in alphabetical order

Key points

Read only the columns and rows an application needs.
Use prepared statements for values and constraints for data integrity.
Scope writes carefully and verify their result.

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