feat(chsql): add GROUP BY

internal/chstorage/chsql/chsql.go

@@ -214,6 +214,11 @@ func (p *Printer) Where() {
 	p.Ident("WHERE")
 }
 
+// Group writes `GROUP` ident.
+func (p *Printer) Group() {
+	p.Ident("GROUP")
+}
+
 // Order writes `ORDER` ident.
 func (p *Printer) Order() {
 	p.Ident("ORDER")

internal/chstorage/chsql/select.go

@@ -21,8 +21,9 @@ type SelectQuery struct {
 	// prewhere is a set of expression joined by AND
 	prewhere []Expr
 	// where is a set of expression joined by AND
-	where []Expr
-	order []orderExpr
+	where   []Expr
+	groupBy []Expr
+	order   []orderExpr
 
 	limit int
 }
@@ -68,6 +69,12 @@ func (q *SelectQuery) Where(filters ...Expr) *SelectQuery {
 	return q
 }
 
+// GroupBy adds grouping to query.
+func (q *SelectQuery) GroupBy(groups ...Expr) *SelectQuery {
+	q.groupBy = append(q.groupBy, groups...)
+	return q
+}
+
 // Order adds order to query.
 func (q *SelectQuery) Order(e Expr, order Order) *SelectQuery {
 	q.order = append(q.order, orderExpr{expr: e, order: order})
@@ -175,6 +182,19 @@ func (q *SelectQuery) WriteSQL(p *Printer) error {
 			}
 		}
 	}
+	if len(q.groupBy) > 0 {
+		p.Group()
+		p.By()
+
+		for i, e := range q.groupBy {
+			if i != 0 {
+				p.Comma()
+			}
+			if err := p.WriteExpr(e); err != nil {
+				return errors.Wrapf(err, "group by %d", i)
+			}
+		}
+	}
 	if len(q.order) > 0 {
 		p.Order()
 		p.By()