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Query Basics
TOP TOP WITH TIES OFFSET FETCH IIF CHOOSE CONCAT STRING_AGG STRING_SPLIT TRY_CAST TRY_CONVERT
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DECLARE variable SET variable SELECT assignment IF ELSE WHILE BREAK CONTINUE BEGIN END GOTO label RETURN code
Data Changes
OUTPUT clause UPDATE FROM DELETE FROM join MERGE IDENTITY insert SCOPE_IDENTITY SEQUENCE Table value constructor SELECT INTO TRUNCATE TABLE
Transactions & Errors
BEGIN TRANSACTION COMMIT TRANSACTION ROLLBACK TRANSACTION SAVE TRANSACTION @@TRANCOUNT XACT_STATE TRY CATCH THROW RAISERROR SET XACT_ABORT
Stored Programming
CREATE PROCEDURE Procedure parameters OUTPUT parameter CREATE FUNCTION Scalar UDF Inline table-valued function Multi-statement TVF EXECUTE procedure sp_executesql Dynamic parameterization
Window & Analytics
ROW_NUMBER RANK DENSE_RANK NTILE LAG LEAD FIRST_VALUE LAST_VALUE PERCENT_RANK Running aggregate
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Local temp table Global temp table Table variable CTE Recursive CTE CROSS APPLY OUTER APPLY PIVOT UNPIVOT VALUES table constructor
SQL Server Features
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T-SQL / Data Changes

MERGE

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

10 min read • Beginner

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

Trace the example line by line. Identify the exact syntax for MERGE, 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-03-04-merge.sql
tsql Try It Live 
MERGE Inventory AS t USING Incoming AS s ON t.sku=s.sku WHEN MATCHED THEN UPDATE SET qty=s.qty WHEN NOT MATCHED THEN INSERT(sku,qty) VALUES(s.sku,s.qty);
Edge case / engineering note

For MERGE, 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

MERGE Mastery Check →
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DELETE FROM join
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IDENTITY insert