将VARCHAR转换为BINARY(16)：SQL Server二进制数据解码问题

Hey there, let’s work through this problem you’re facing—binary data stored in a varchar(400) column (SomeData in TABLE_TEST) that shows up fine when editing the table but garbles or doesn’t display correctly when running a SELECT query. I’ve helped folks with this exact scenario before, so let’s break down actionable solutions:

1. First, View the Raw Binary as Hexadecimal #

The reason you can see the data in the table editor is likely because it’s rendering the binary content as hexadecimal, while a plain SELECT tries to interpret the varchar as text (which fails for non-printable binary bytes). To match what you see in the editor, convert the varchar to varbinary to get the raw hex representation:

SELECT CAST(SomeData AS VARBINARY(400)) AS RawBinaryHex
FROM TABLE_TEST;

Or using CONVERT (same end result):

SELECT CONVERT(VARBINARY(400), SomeData) AS RawBinaryHex
FROM TABLE_TEST;

This query will return the hexadecimal string of your binary data, just like what’s shown in the table edit interface.

2. Decode to Readable Text (If Applicable) #

If the binary data was originally text (e.g., ASCII or Unicode) that got stored as varchar by mistake, you can convert it back after first casting to varbinary:

• For ASCII/ANSI text:

  SELECT CONVERT(VARCHAR(400), CAST(SomeData AS VARBINARY(400))) AS DecodedText
  FROM TABLE_TEST;
  

• For Unicode (UTF-16) text:

  SELECT CONVERT(NVARCHAR(200), CAST(SomeData AS VARBINARY(400))) AS DecodedUnicodeText
  FROM TABLE_TEST;
  

Note: If the binary data is something non-text (like encrypted content, compressed data, or file blobs), this won’t work—you’ll need to use the appropriate decryption/decompression functions for that specific data type.

3. Handle Hexadecimal Strings Stored as VARCHAR #

If the SomeData column actually stores hexadecimal strings (e.g., "0x1F8B0800..." or "1F8B0800...") instead of raw binary, you’ll need to convert those string values to actual binary data first:

• For strings with the 0x prefix:

  SELECT CONVERT(VARBINARY(400), SomeData, 1) AS ActualBinaryData
  FROM TABLE_TEST;
  

• For strings without the 0x prefix:

  SELECT CONVERT(VARBINARY(400), SomeData, 2) AS ActualBinaryData
  FROM TABLE_TEST;
  

Once you have the actual binary data, you can then convert it to whatever format you need (text, etc.).

Why Your Previous Conversion Attempts Might Have Failed #

Chances are you tried converting the varchar directly without first casting it to varbinary. Since varchar is a character type, any non-printable binary bytes get treated as invalid characters, which breaks string-based conversions. Always start by casting to varbinary to retrieve the original binary data before any further processing.

内容的提问来源于stack exchange，提问作者user7867434