Avoiding Invalid Key Types

Index Column Data Types in Azure SQL Database

Avoiding Invalid Key Types

When creating indexes in Azure SQL Database, it's essential to choose appropriate data types for the key columns to ensure optimal performance and data integrity. Microsoft has imposed certain restrictions on data types that can be used as key columns due to limitations in SQL Server's indexing mechanism. This article aims to shed light on these restrictions and guide you in selecting the correct data types to avoid the error "Column key in table misc_info is of a type that is invalid for use as a key column in an index."

Specific Error Messages

• "An indexs key cannot exceed a total size of 900 bytes"
• "Change the data type to NVARCHAR450"
• "Column XX in table dboYY is of a type that is invalid for use as a key column in an index"
• "Column ColumnName in table schemaTableName is of a type that is invalid for use as a key column in an index"

These error messages typically indicate that the data type of the column you're attempting to index is not suitable as a key column. To resolve the issue, you need to change the data type to one that is permitted for use as a key.