Add func expression support.

sqlbuilder/func.go

@@ -0,0 +1,57 @@
+package sqlbuilder
+
+import "bytes"
+
+type FuncExpression struct {
+	isExpression
+	isProjection
+
+	name       string
+	expression Expression
+
+	alias string
+}
+
+func (f *FuncExpression) As(alias string) Projection {
+	newFuncExpression := *f
+
+	newFuncExpression.alias = alias
+
+	return &newFuncExpression
+}
+
+func (f *FuncExpression) SerializeSql(out *bytes.Buffer) error {
+	out.WriteString(f.name)
+	out.WriteString("(")
+	err := f.expression.SerializeSql(out)
+	if err != nil {
+		return err
+	}
+	out.WriteString(")")
+
+	if f.alias != "" {
+		out.WriteString(` AS "`)
+		out.WriteString(f.alias)
+		out.WriteString(`"`)
+	}
+
+	return nil
+}
+
+func (f *FuncExpression) SerializeSqlForColumnList(out *bytes.Buffer) error {
+	return f.SerializeSql(out)
+}
+
+func MAX(expression Expression) *FuncExpression {
+	return &FuncExpression{
+		name:       "MAX",
+		expression: expression,
+	}
+}
+
+func SUM(expression Expression) *FuncExpression {
+	return &FuncExpression{
+		name:       "SUM",
+		expression: expression,
+	}
+}