revert wrong changes

statistics/histogram.go

@@ -979,6 +979,12 @@ func (hg *Histogram) outOfRangeRowCount(lDatum, rDatum *types.Datum, modifyCount
 		totalPercent = 1
 	}
 	rowCount := totalPercent * hg.notNullCount()
+
+	// Use the modifyCount as the upper bound. Note that modifyCount contains insert, delete and update. So this is
+	// a rather loose upper bound.
+	// There are some scenarios where we need to handle out-of-range estimation after both insert and delete happen.
+	// But we don't know how many increases are in the modifyCount. So we have to use this loose bound to ensure it
+	// can produce a reasonable results in this scenario.
 	if rowCount > float64(modifyCount) {
 		return float64(modifyCount)
 	}
@@ -2118,6 +2124,8 @@ func MergePartitionHist2GlobalHist(sc *stmtctx.StatementContext, hists []*Histog
 			if types.IsTypeTime(hists[0].Tp.GetType()) {
 				// handle datetime values specially since they are encoded to int and we'll get int values if using DecodeOne.
 				_, d, err = codec.DecodeAsDateTime(meta.Encoded, hists[0].Tp.GetType(), sc.TimeZone)
+			} else if types.IsTypeFloat(hists[0].Tp.GetType()) {
+				_, d, err = codec.DecodeAsFloat32(meta.Encoded, hists[0].Tp.GetType())
 			} else {
 				_, d, err = codec.DecodeOne(meta.Encoded)
 			}