Adds the SIGN function which returns the positive (+1), zero (0), or negative (-1) sign of a numeric expression.

Changes

• ExpressionFunctions.cs — six overloads covering all supported numeric types: int, bigint, decimal, float, money, real
• FunctionMetadata.cs — autocomplete/IntelliSense entry
• ExpressionFunctionTests.cs — unit tests for int, bigint, and float overloads covering positive, negative, zero, and null inputs

Usage

SELECT SIGN(-42)     -- -1
SELECT SIGN(0)       -- 0
SELECT SIGN(3.14)    -- 1
SELECT SIGN(amount)  -- works on any numeric column