A place for code I want to explain, mistakes worth remembering, and the occasional story from my life.
Laravel 2 min read
An authenticated user changes an invoice ID in the address bar. Login proves who the user is; it does not prove that this invoice belongs to them. Put the ownership rule in the app...
MySQL 2 min read
A “latest products” widget uses LIMIT 10 without ORDER BY and appears correct on a small database. After an index or query-plan change, it shows different records. SQL does not pro...
MySQL 2 min read
A supplier treats ab-12 and AB-12 as different identifiers, but a case-insensitive database collation considers them equal. A uniqueness failure or unexpected lookup may be a colla...
MySQL 2 min read
A dashboard with no invoices shows a blank balance because SUM over no matching rows returns NULL. For a known empty set, displaying zero can be appropriate, but that choice should...
MySQL 2 min read
A large export fails halfway through. Restarting with a deep OFFSET is slow and can shift if rows are inserted or removed. A stable-key checkpoint gives the exporter a clearer resu...
MySQL 2 min read
An import wraps its writes in a transaction, throws an exception, and still leaves changes behind. Before blaming the framework, verify that the tables involved use an engine with...
MySQL 2 min read
A MySQL DECIMAL column stores an exact decimal value, but application code immediately casts it to float. The database choice alone cannot preserve exactness after that conversion....
MySQL 2 min read
Two staff members open the same product form. The second save overwrites the first person's correction. A version column can detect that the submitted form is based on an older rec...
MySQL 2 min read
One transfer locks account A then account B. Another locks B then A. Each can wait for the row held by the other, creating a deadlock. Consistent lock ordering reduces this avoidab...
