Function analyze_schema_expression 

pub fn analyze_schema_expression(
    context: &SchemaBindingContext<'_, '_>,
    expression: &Expr,
    columns: &[ColumnDef],
) -> Result<AnalyzedSchemaExpression, SQLError>

Analyze every branch before planning, and bind original routine/type/input identities for storage. Assignment coercion follows the planner’s mutability check.