SQL Server Tip: TRY_CONVERT vs CAST in SQL Server

Overview

In SQL Server, data type conversion is a common necessity, often addressed by functions such asCASTandTRY_CONVERT. While both serve to convert data from one type to another, they differ significantly in error handling.CASTwill generate an error when conversion fails, whileTRY_CONVERTreturns NULL instead.

Prerequisites

• SQL Server (2012 or later recommended)
• SQL Server Management Studio (SSMS)
• Basic understanding of SQL queries

Step-by-step

1) Using CAST

To demonstrate the use ofCAST, let's convert a string to an integer. The following query will fail if the string cannot be converted:

sql

SELECT CAST('123' AS INT) AS ConvertedValue, CAST('ABC' AS INT) AS FailedConversion;

2) Using TRY_CONVERT

Now let's useTRY_CONVERTto handle the same conversion gracefully. This method will return NULL if the conversion fails:

sql

SELECT TRY_CONVERT(INT, '123') AS ConvertedValue, TRY_CONVERT(INT, 'ABC') AS FailedConversion;

• This error occurs when using
• Assuming both functions behave the same. Always consider using

Quick Checklist

• Prerequisites (tools/versions) are listed clearly.
• Setup steps are complete and reproducible.
• Include at least one runnable code example (SQL/Python/YAML).
• Explain why each step matters (not just how).
• Add Troubleshooting/FAQ for common errors.

Applied Example

Mini-project idea: Implement an incremental load in dbt using a staging table and a window function for change detection. Show model SQL, configs, and a quick test.

FAQ

What versions/tools are required?

List exact versions of Snowflake/dbt/Airflow/SQL client to avoid env drift.

How do I test locally?

Use a dev schema and seed sample data; add one unit test and one data test.

Common error: permission denied?

Check warehouse/role/database privileges; verify object ownership for DDL/DML.

Related Reading

• SQL Server Tip: Understanding Window Functions - ROW_NUMBER, RANK, DENSE_RANK