This implements type inference for MySQL mathematical expressions. Before this change, queries with arithmetic operations would generateinterface{} types, which meant no compile-time type safety. Now the compiler properly infers types based on the operands and operators.

Before:

typeListTestRowstruct {A1Floatinterface{}`json:"a1_float"`// was interface{}}

After:

typeListTestRowstruct {A1Floatstring`json:"a1_float"`// now string (MySQL DECIMAL)}

What changed

• AddedinferExprType() that recursively analyzes SQL expressions to determine their types
• Handles column references, constants, binary operations, and type casts
• MySQL-specific type rules: division returns decimal, float operations return float, nullability propagates correctly
• Enhanced COALESCE to use type inference instead of always returninginterface{}
• Added "div" and "mod" to the mathematical operators list (MySQL uses symbolic names instead of/ and%)

Notes

The implementation is MySQL-specific for now. PostgreSQL and SQLite returnnil fromcombineGenericTypes() to maintain current behavior. There's a TODO comment about refactoringIsMathematicalOperator() to be engine-specific.

Closes#4153