importer: support rand date by stats (pingcap#5830)

cmd/importer/db.go

@@ -210,7 +210,7 @@ func genColumnData(table *table, column *column) (string, error) {
 		if isUnique {
 			data = append(data, []byte(column.data.uniqDate())...)
 		} else {
-			data = append(data, []byte(randDate(column.min, column.max))...)
+			data = append(data, []byte(randDate(column))...)
 		}
 
 		data = append(data, '\'')

cmd/importer/rand.go

@@ -74,7 +74,12 @@ func randDuration(n time.Duration) time.Duration {
 	return time.Duration(duration)
 }
 
-func randDate(min string, max string) string {
+func randDate(col *column) string {
+	if col.hist != nil {
+		return col.hist.randDate()
+	}
+
+	min, max := col.min, col.max
 	if len(min) == 0 {
 		year := time.Now().Year()
 		month := randInt(1, 12)

cmd/importer/stats.go

@@ -17,10 +17,12 @@ import (
 	"encoding/json"
 	"io/ioutil"
 	"math/rand"
+	"time"
 
 	"github.com/juju/errors"
 	"github.com/pingcap/tidb/model"
 	stats "github.com/pingcap/tidb/statistics"
+	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/chunk"
 	"github.com/pingcap/tidb/util/codec"
 	"github.com/pingcap/tidb/util/mock"
@@ -132,3 +134,32 @@ func (h *histogram) randString() string {
 	}
 	return h.Bounds.GetRow(idx).GetString(0)
 }
+
+// randDate randoms a bucket and random a date between upper and lower bound.
+func (h *histogram) randDate() string {
+	idx := h.getRandomBoundIdx()
+	if idx%2 == 0 {
+		lower := h.Bounds.GetRow(idx).GetTime(0)
+		upper := h.Bounds.GetRow(idx + 1).GetTime(0)
+		diff := types.TimestampDiff("DAY", lower, upper)
+		if diff == 0 {
+			str, err := lower.DateFormat("%Y-%m-%d")
+			if err != nil {
+				log.Fatal(err)
+			}
+			return str
+		}
+		delta := randInt(0, int(diff)-1)
+		l, err := lower.Time.GoTime(time.Local)
+		if err != nil {
+			log.Fatal(err)
+		}
+		l = l.AddDate(0, 0, delta)
+		return l.Format(dateFormat)
+	}
+	str, err := h.Bounds.GetRow(idx).GetTime(0).DateFormat("%Y-%m-%d")
+	if err != nil {
+		log.Fatal(err)
+	}
+	return str
+}