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.
Select one whole event per account with an explicit tie-breaker and a deliberate policy for missing timestamps.
A detailed technical breakdown of the differences between WHERE and HAVING clauses, focusing on execution order, aggregate function compatibility, and performance optimization strategies.
Find the expensive step and distinguish estimates from measurements.