Great question! It’s totally normal to notice this kind of visual discrepancy even when the underlying stored values are correct—let’s break down exactly why this happens:

1. Floating-Point Numbers Are Approximations by Nature #

First, remember that double (both in C# and most SQL databases like SQL Server’s FLOAT(53)) follows the IEEE 754 double-precision standard. This means decimal values like 0.1 or 0.8 can’t be represented perfectly as binary fractions.

Even if you set your entity’s T12 property to 0.8, the actual value stored in memory is a tiny approximation (like 0.8000000000000000444...). The database stores this exact binary approximation, but when you query it, the database’s tooling (like SSMS) or SQL engine will format that binary value into a human-readable string—often rounding it to a more friendly decimal representation (like 0.8) instead of showing the full precision.

2. .NET vs. SQL Have Different Default Formatting Rules #

The way each system converts the binary floating-point value to a string is what creates the visual gap:

• In .NET, when you inspect a double property (say, in the debugger) or call ToString() without parameters, it will typically display up to 15-17 significant digits to reflect the full precision of the IEEE 754 standard. So that tiny approximation in memory gets shown as 0.8000000000000001 instead of 0.8.
• SQL databases, on the other hand, usually default to formatting double/float values to a concise, human-friendly string. For example, SQL Server will often round to the shortest decimal string that maps back to the same binary value, so it shows 0.8 instead of the full precision.

3. Linq2Db Uses Parameterization (Not String Injection) #

Linq2Db doesn’t convert your double values to strings and inject them into SQL queries—it uses parameterized queries. That means it sends the raw binary double value directly to the database, which is why the stored value is correct. The "difference" you’re seeing is only in how the value is displayed on each side, not in the actual data being stored or transferred.

How to Make the Representations Match #

If you want consistent display between your C# code and SQL queries:

• In C#, use explicit formatting when displaying values, like T12.ToString("F1") to force 1 decimal place.
• In SQL, use the FORMAT function to control output, like FORMAT(T12, 'N1') to show exactly 1 decimal digit.

Just remember: the underlying values are identical—this is purely a display/formatting issue caused by how each system handles floating-point to string conversion.

内容的提问来源于stack exchange，提问作者Jarosław