Add StringColumn type and expression

Add Projection type
Alias refactoring
More numeric operations

sqlbuilder/func.go

@@ -2,22 +2,31 @@ package sqlbuilder
 
 import "bytes"
 
-type FuncExpression struct {
+type FuncExpression interface {
+	Expression
+}
+
+type numericFunc struct {
+	expressionInterfaceImpl
+	numericInterfaceImpl
+
 	name       string
 	expression Expression
-
-	alias string
 }
 
-func (f *FuncExpression) As(alias string) Clause {
-	newFuncExpression := *f
+func NewNumericFunc(name string, expression Expression) NumericExpression {
+	numericFunc := &numericFunc{
+		name:       name,
+		expression: expression,
+	}
 
-	newFuncExpression.alias = alias
+	numericFunc.expressionInterfaceImpl.parent = numericFunc
+	numericFunc.numericInterfaceImpl.parent = numericFunc
 
-	return &newFuncExpression
+	return numericFunc
 }
 
-func (f *FuncExpression) SerializeSql(out *bytes.Buffer, options ...serializeOption) error {
+func (f *numericFunc) SerializeSql(out *bytes.Buffer, options ...serializeOption) error {
 	out.WriteString(f.name)
 	out.WriteString("(")
 	err := f.expression.SerializeSql(out)
@@ -26,12 +35,6 @@ func (f *FuncExpression) SerializeSql(out *bytes.Buffer, options ...serializeOpt
 	}
 	out.WriteString(")")
 
-	if f.alias != "" {
-		out.WriteString(` AS "`)
-		out.WriteString(f.alias)
-		out.WriteString(`"`)
-	}
-
 	return nil
 }
 
@@ -39,16 +42,10 @@ func (f *FuncExpression) SerializeSql(out *bytes.Buffer, options ...serializeOpt
 //	return f.SerializeSql(out)
 //}
 
-func MAX(expression Expression) *FuncExpression {
-	return &FuncExpression{
-		name:       "MAX",
-		expression: expression,
-	}
+func MAX(expression NumericExpression) NumericExpression {
+	return NewNumericFunc("MAX", expression)
 }
 
-func SUM(expression Expression) *FuncExpression {
-	return &FuncExpression{
-		name:       "SUM",
-		expression: expression,
-	}
+func SUM(expression NumericExpression) NumericExpression {
+	return NewNumericFunc("SUM", expression)
 }