All 7 Dynamic SQL questions
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What is SQL injection, and how does it relate to writing dynamic SQL unsafely? How do you safely use sp_executesql to execute dynamic SQL with parameters, avoiding the risks of simple string concatenation? How would you build a dynamic SQL query where the table or column names themselves need to change based on input, since parameters cannot be used for object names? How do you debug a dynamic SQL statement when it fails or does not produce the expected results? How would you build a dynamic SQL statement inside a stored procedure that constructs a flexible search query based on several optional filter parameters? What are the performance tradeoffs of using dynamic SQL compared to static, precompiled SQL statements?
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SQL Server › Dynamic SQL

What is dynamic SQL, and why would you need to build and execute a SQL statement as a string rather than writing it directly?

Beginner

Answer

Dynamic SQL means building a SQL statement as a text string at runtime and then executing it, which is useful when parts of your query, such as the table name or the columns being sorted by, are not known ahead of time and depend on some condition or user input determined while the program is running.
DECLARE @TableName NVARCHAR(100) = 'Orders';
DECLARE @SQL NVARCHAR(MAX) = 'SELECT * FROM ' + @TableName;
EXEC (@SQL);
Real-world example A reporting tool lets users choose which table to generate a report from through a dropdown menu, using dynamic SQL to build the correct query based on whichever table the user actually selected.

Common follow-ups: What are the security risks associated with building dynamic SQL from user input?;What is the difference between using EXEC and sp_executesql to run dynamic SQL?

Stored Procedures & Functions;Error Handling with TRY CATCH
All 7 Dynamic SQL questions