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T-SQL / Temporary Data

OUTER APPLY

Learn OUTER APPLY in T-SQL through a focused explanation, a dedicated construct-specific example, an engineering boundary, and a mastery check.

10 min read • Advanced

OUTER APPLY is an atomic T-SQL topic inside Temporary Data. This lesson focuses on how the OUTER APPLY construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for OUTER APPLY, 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

tsql-07-07-outer-apply.sql
tsql Try It Live 
SELECT c.id,o.id last_order FROM Customers c OUTER APPLY (SELECT TOP 1 id FROM Orders o WHERE o.customer_id=c.id ORDER BY created_at DESC) o;
Edge case / engineering note

For OUTER APPLY, 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.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

OUTER APPLY Mastery Check →
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