qb: add named limit and per partition limit clauses

qb/limit.go

@@ -0,0 +1,45 @@
+// Copyright (C) 2017 ScyllaDB
+// Use of this source code is governed by a ALv2-style
+// license that can be found in the LICENSE file.
+
+package qb
+
+import (
+	"bytes"
+	"strconv"
+)
+
+type limit struct {
+	value        value
+	perPartition bool
+}
+
+func limitLit(l uint, perPartition bool) limit {
+	val := strconv.FormatUint(uint64(l), 10)
+	return limit{
+		value:        lit(val),
+		perPartition: perPartition,
+	}
+}
+
+func limitNamed(name string, perPartition bool) limit {
+	return limit{
+		value:        param(name),
+		perPartition: perPartition,
+	}
+}
+
+func (l limit) writeCql(cql *bytes.Buffer) (names []string) {
+	if l.value == nil {
+		return nil
+	}
+
+	if l.perPartition {
+		cql.WriteString("PER PARTITION ")
+	}
+	cql.WriteString("LIMIT ")
+
+	names = l.value.writeCql(cql)
+	cql.WriteByte(' ')
+	return
+}