Materials on AI, Python, Git, SQL, Web/API, SAP/ERP, statistics and time series: explanations, examples, practical tips, sources and applicability limits.
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Compare RESTRICT, CASCADE and SET NULL using a small isolated example, then check the actual constraint and dependent rows before changing real data.
A closer look at explicitly deferred NO ACTION checks and clearing only the optional component of a composite foreign key. These details complement the basic choice between RESTRICT, CASCADE and SET NULL.
Diagnose repeated JOIN rows by counting matching keys, checking constraints and choosing whether the result should contain orders, items or summaries.