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Running total
Learn Running total in SQL through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.
Running total is an atomic SQL topic inside Window Functions. This lesson focuses on how the Running total construct is written, what it changes, and when it is the right tool.
Trace the example line by line. Identify the exact syntax for Running total, the input state before it runs, and the resulting value, control flow, database state, hardware behavior, or runtime effect afterward. Neighboring lessons use different constructs rather than renamed copies of this one.
Topic-specific example
SELECT id,amount,SUM(amount) OVER (ORDER BY id ROWS UNBOUNDED PRECEDING) AS balance FROM ledger;
For Running total, test the boundary that belongs to this exact feature rather than a generic failure case. Check invalid or empty input, NULL/unknown state, numeric limits, transaction or exception behavior, synthesis/runtime constraints, ownership/permission rules, or backtracking/control-flow effects where they apply.