How to fix Error 4077 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4077 — sql_variant Collation Mismatch

Why This Error Happens

This error occurs when a sql_variant column stores character data using a collation that differs from the database’s or instance’s default collation, and an operation (such as a comparison, sort, or UNION) cannot implicitly resolve which collation to use. SQL Server 2025 requires explicit collation context when comparing or combining sql_variant values that originated from columns or variables with mismatched collations. This typically happens after a database restore from a server with a different default collation, or when linking tables from different instances via linked servers.

Step-by-Step Resolution Guide

Step 1: Identify the Conflicting Collations

  • Run SELECT SQL_VARIANT_PROPERTY(column_name, 'Collation') FROM table_name; to inspect the stored collation of the sql_variant value.
  • Compare this against your database default: SELECT DATABASEPROPERTYEX('YourDB', 'Collation');
  • Note any mismatch, especially after migrating databases to SQL Server 2025 on Windows Server 2025/Windows 11.

Step 2: Apply an Explicit COLLATE Clause

  • Modify the failing query to cast the sql_variant value explicitly, e.g.:
    SELECT * FROM table_name WHERE CAST(column_name AS NVARCHAR(100)) COLLATE DATABASE_DEFAULT = 'value';
  • For comparisons between two sql_variant columns, apply COLLATE DATABASE_DEFAULT to both sides of the expression.
  • Save and re-run the query to confirm the error no longer appears.

Step 3: Align Database and Instance Collations

  • Open SQL Server Management Studio (SSMS) and right-click the instance → Properties → General to check the server-level collation.
  • If the database was restored from another system, consider rebuilding the affected table with a consistent collation using:
    ALTER TABLE table_name ALTER COLUMN column_name sql_variant COLLATE DATABASE_DEFAULT;
  • Restart the SQL Server service via Services.msc (Windows Server 2025/Windows 11) if collation metadata needs to refresh.

Step 4: Update Linked Server or ETL Collation Settings

  • If the data originates from a linked server, open Linked Servers in SSMS → Properties → Server Options, and ensure “Collation Compatible” is set to True if collations match.
  • For SSIS/ETL pipelines, verify the data flow task’s collation metadata matches the destination database.

Alternative or Verification Steps

  • Re-run the original failing query/report in SSMS; successful execution without Error 4077 confirms the fix.
  • As an alternative, if widespread mismatches exist, export the sql_variant data to a staging table using CAST(... AS NVARCHAR) with explicit COLLATE DATABASE_DEFAULT, then re-import to normalize collation across the dataset.