Materials on AI, Python, Git, SQL, Web/API, SAP/ERP, statistics and time series: explanations, examples, practical tips, sources and applicability limits.
Every word must appear in the article. Use quotes for an exact phrase.
Compare RESTRICT, CASCADE and SET NULL using a small isolated example, then check the actual constraint and dependent rows before changing real data.
Selecting the right ON DELETE action is a data-retention decision, not a syntax choice. RESTRICT protects dependents, CASCADE removes lifecycle children, and SET NULL preserves rows with optional references.
Diagnose repeated JOIN rows by counting matching keys, checking constraints and choosing whether the result should contain orders, items or summaries.