How to fix Error 3800 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: Error 3800 in SQL Server 2025

Why This Error Happens

This error occurs when SQL Server’s internal column-name comparison logic detects that two or more column names within the same table are too similar, typically differing only by case sensitivity, trailing whitespace, or Unicode normalization variants that collate to the same binary representation. SQL Server 2025 enforces stricter column-name differentiation checks during CREATE TABLE or ALTER TABLE operations to prevent ambiguity in collation-insensitive lookups, metadata caching, and columnstore index operations. This is often triggered by scripts generated from ORMs, migration tools, or copy-pasted DDL where names like OrderID and orderid (or Name with a trailing space) are used in the same schema.

Step-by-Step Resolution Guide

Step 1: Identify the Conflicting Column Names

  • Open the DDL script or run sp_help 'YourTableName' in SQL Server Management Studio (SSMS) to list all existing columns.
  • Look for columns that appear nearly identical, especially differing only in case (e.g., UserID vs userid) or hidden characters (trailing spaces, tabs, or non-breaking Unicode spaces copied from Word/Excel).
  • Use the query below to detect whitespace or hidden characters in column names:
  SELECT name, LEN(name) AS actual_length, DATALENGTH(name) AS byte_length
  FROM sys.columns
  WHERE object_id = OBJECT_ID('YourTableName');

Step 2: Correct the Column Definitions in the Script

  • Rename one of the conflicting columns to a clearly distinct name (e.g., change orderid to Order_Reference_ID).
  • If the issue stems from copy-pasted text, retype the column name manually in a plain text editor (like Notepad) to strip any invisible Unicode characters, then paste it back into SSMS.
  • Save the corrected script, for example at C:\Scripts\FixedSchema.sql.

Step 3: Check Server Collation Settings

  • Verify the database collation using:
  SELECT DATABASEPROPERTYEX('YourDatabaseName', 'Collation');
  • If the collation is case-insensitive (e.g., SQL_Latin1_General_CP1_CI_AS), ensure new column names are not relying on case alone to differentiate them, as SQL Server 2025 will reject this during table creation or alteration.
  • Adjust the collation at the column level if a case-sensitive exception is required:
  ALTER TABLE YourTableName
  ALTER COLUMN YourColumnName VARCHAR(50) COLLATE SQL_Latin1_General_CP1_CS_AS;

Step 4: Re-run the DDL Statement

  • Execute the corrected CREATE TABLE or ALTER TABLE statement in SSMS or via sqlcmd:
  sqlcmd -S YourServerName -d YourDatabaseName -i C:\Scripts\FixedSchema.sql
  • Confirm no Error 3800 is thrown and the table structure updates successfully.

Alternative or Verification Steps

  • Run sp_columns YourTableName after applying the fix to visually confirm all column names are now distinct and correctly spelled.
  • If the error persists despite visually correct names, rebuild the script from scratch in Notepad (avoiding copy-paste from PDFs or web pages) to eliminate any residual Unicode homoglyphs or zero-width characters.