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Query Basics
TOP TOP WITH TIES OFFSET FETCH IIF CHOOSE CONCAT STRING_AGG STRING_SPLIT TRY_CAST TRY_CONVERT
Variables & Flow
DECLARE variable SET variable SELECT assignment IF ELSE WHILE BREAK CONTINUE BEGIN END GOTO label RETURN code
Data Changes
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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
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T-SQL / Variables & Flow

DECLARE variable

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

10 min read • Beginner

DECLARE variable is an atomic T-SQL topic inside Variables & Flow. This lesson focuses on how the DECLARE variable construct is written, what it changes, and when it is the right tool.

Trace the example line by line. Identify the exact syntax for DECLARE variable, 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-02-01-declare-variable.sql
tsql Try It Live 
DECLARE @count int=3; SELECT @count;
Edge case / engineering note

For DECLARE variable, 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

DECLARE variable Mastery Check →
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SET variable