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695. JOIN with CONVERT

Understand how CONVERT can be used to transform data types during JOIN operations.

📘 Lesson 695 of 728 ⏱ 14 min 🎯 Advanced

CONVERT is a database-specific function, commonly associated with SQL Server, that changes a value from one data type to another.

It can help connect data stored in different formats, especially in legacy or integration scenarios.

Convert a character customer ID before matching it to a numeric identifier.

SQL 
SELECT
    c.CustomerName,
    r.RiskCategory
FROM Customers c
INNER JOIN RiskRecords r
    ON CONVERT(VARCHAR(20), c.CustomerID) = r.CustomerID;

Used in SQL Server reporting, legacy integrations, migrations, and data cleanup.

  • CONVERT is commonly used in SQL Server.
  • It can perform explicit data-type conversion.
  • Conversion formats can be specified for some data types.
  • Invalid conversions can produce errors.
  • Cross-database portability should be considered.
What is CONVERT used for?

CONVERT changes a value from one data type to another in database systems that support the function.

Is CONVERT standard across all databases?

No. CONVERT is particularly associated with SQL Server, while other systems may use CAST or different functions.

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