How to fix Error 8156 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 8156 — “The column ‘%.ls’ was specified multiple times for ‘%.ls'”

Why This Error Happens

This error occurs when a Transact-SQL statement—typically a SELECT INTO, CREATE VIEW, JOIN, or INSERT with column aliasing—references the same column name more than once within a single result set or table definition without proper disambiguation. SQL Server 2025’s query compiler enforces strict uniqueness on output column names because downstream operations (indexing, metadata generation, or ORM mapping) cannot resolve ambiguous duplicate identifiers. This is most commonly caused by joining two tables that share a column name (e.g., ID) without using aliases, or by a poorly constructed UNION/PIVOT query that fails to rename overlapping fields.

Step-by-Step Resolution Guide

Step 1: Identify the Offending Query

  • Capture the exact query text from the SQL Server error log or SSMS output pane, since the error message includes the specific column and object name (%.*ls).
  • Check C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Log\ERRORLOG on Windows Server 2025 for the full statement context if the error occurred via a scheduled job or application call.
  • Run the query manually in SSMS or Azure Data Studio to reproduce the error and confirm the line number.

Step 2: Audit the SELECT List or JOIN Conditions

  • Look for duplicate column names pulled from two different tables in a JOIN, such as SELECT a.ID, b.ID FROM TableA a JOIN TableB b ON a.FK = b.ID.
  • Add explicit aliases to differentiate every column: SELECT a.ID AS TableA_ID, b.ID AS TableB_ID.
  • If using SELECT * in a multi-table join, replace it with an explicit column list to avoid hidden duplicates introduced by schema changes.

Step 3: Correct CREATE VIEW or SELECT INTO Statements

  • For SELECT ... INTO NewTable, ensure every computed or joined column has a unique alias before execution.
  • For CREATE VIEW, explicitly define the column list in the view header (e.g., CREATE VIEW vSales (SaleID, CustomerID, OrderDate) AS ...) to force uniqueness.
  • Re-run sp_help 'ViewName' after the fix to confirm no duplicate metadata entries remain.

Step 4: Rebuild and Validate Dependent Objects

  • If the error surfaced during a deployment script or DACPAC/SSDT build, open the .sql project file and search for the affected object name reported in the error.
  • Use sqlpackage.exe with the /p:BlockOnPossibleDataLoss=false flag only after confirming the script compiles cleanly in a test environment.
  • Recompile stored procedures or views using sp_refreshsqlmodule once column references are corrected.

Alternative or Verification Steps

  • Re-execute the corrected query or redeploy the view/procedure and confirm it returns a result set without Error 8156 in SSMS or the Windows Event Viewer (Applications and Services Logs > MSSQLSERVER).
  • If the error persists in a third-party application connecting via ODBC/JDBC, enable SQL Server Profiler or Extended Events to trace the exact auto-generated query, as the duplication may originate from the application’s query builder rather than manually written T-SQL.