Golang influxql.Reduce函数代码示例

func expandExprWithValues(expr influxql.Expr, keys []string, tagExprs []tagExpr, uniques [][]string, index int) []tagSetExpr {
	// If we have no more keys left then execute the reduction and return.
	if index == len(keys) {
		// Create a map of tag key/values.
		m := make(map[string]*string, len(keys))
		for i, key := range keys {
			if tagExprs[i].op == influxql.EQ {
				m[key] = &tagExprs[i].values[0]
			} else {
				m[key] = nil
			}
		}

		// TODO: Rewrite full expressions instead of VarRef replacement.

		// Reduce using the current tag key/value set.
		// Ignore it if reduces down to "false".
		e := influxql.Reduce(expr, &tagValuer{tags: m})
		if e, ok := e.(*influxql.BooleanLiteral); ok && e.Val == false {
			return nil
		}

		return []tagSetExpr{{values: copyTagExprs(tagExprs), expr: e}}
	}

	// Otherwise expand for each possible equality value of the key.
	var exprs []tagSetExpr
	for _, v := range uniques[index] {
		exprs = append(exprs, expandExprWithValues(expr, keys, append(tagExprs, tagExpr{keys[index], []string{v}, influxql.EQ}), uniques, index+1)...)
	}
	exprs = append(exprs, expandExprWithValues(expr, keys, append(tagExprs, tagExpr{keys[index], uniques[index], influxql.NEQ}), uniques, index+1)...)

	return exprs
}

// PlanSelect creates an execution plan for the given SelectStatement and returns an Executor.
func (q *QueryExecutor) PlanSelect(stmt *influxql.SelectStatement, chunkSize int) (Executor, error) {
	// It is important to "stamp" this time so that everywhere we evaluate `now()` in the statement is EXACTLY the same `now`
	now := time.Now().UTC()
	opt := influxql.SelectOptions{}

	// Replace instances of "now()" with the current time, and check the resultant times.
	stmt.Condition = influxql.Reduce(stmt.Condition, &influxql.NowValuer{Now: now})
	opt.MinTime, opt.MaxTime = influxql.TimeRange(stmt.Condition)
	if opt.MaxTime.IsZero() {
		opt.MaxTime = now
	}
	if opt.MinTime.IsZero() {
		opt.MinTime = time.Unix(0, 0)
	}

	// Expand regex sources to their actual source names.
	sources, err := q.Store.ExpandSources(stmt.Sources)
	if err != nil {
		return nil, err
	}
	stmt.Sources = sources

	// Convert DISTINCT into a call.
	stmt.RewriteDistinct()

	// Remove "time" from fields list.
	stmt.RewriteTimeFields()

	// Filter only shards that contain date range.
	shardIDs, err := q.MetaClient.ShardIDsByTimeRange(stmt.Sources, opt.MinTime, opt.MaxTime)
	if err != nil {
		return nil, err
	}
	shards := q.Store.Shards(shardIDs)

	// Rewrite wildcards, if any exist.
	tmp, err := stmt.RewriteWildcards(Shards(shards))
	if err != nil {
		return nil, err
	}
	stmt = tmp

	// Create a set of iterators from a selection.
	itrs, err := influxql.Select(stmt, Shards(shards), &opt)
	if err != nil {
		return nil, err
	}

	// Generate a row emitter from the iterator set.
	em := influxql.NewEmitter(itrs, stmt.TimeAscending())
	em.Columns = stmt.ColumnNames()
	em.OmitTime = stmt.OmitTime

	// Wrap emitter in an adapter to conform to the Executor interface.
	return (*emitterExecutor)(em), nil
}

func (e *StatementExecutor) executeDeleteSeriesStatement(stmt *influxql.DeleteSeriesStatement, database string) error {
	if dbi := e.MetaClient.Database(database); dbi == nil {
		return influxql.ErrDatabaseNotFound(database)
	}

	// Convert "now()" to current time.
	stmt.Condition = influxql.Reduce(stmt.Condition, &influxql.NowValuer{Now: time.Now().UTC()})

	// Locally delete the series.
	return e.TSDBStore.DeleteSeries(database, stmt.Sources, stmt.Condition)
}

// Ensure an expression can be reduced.
func TestReduce(t *testing.T) {
	now := mustParseTime("2000-01-01T00:00:00Z")

	for i, tt := range []struct {
		in   string
		out  string
		data Valuer
	}{
		// Number literals.
		{in: `1 + 2`, out: `3`},
		{in: `(foo*2) + ( (4/2) + (3 * 5) - 0.5 )`, out: `(foo * 2) + 16.500`},
		{in: `foo(bar(2 + 3), 4)`, out: `foo(bar(5), 4)`},
		{in: `4 / 0`, out: `0.000`},
		{in: `1 / 2`, out: `0.500`},
		{in: `4 = 4`, out: `true`},
		{in: `4 <> 4`, out: `false`},
		{in: `6 > 4`, out: `true`},
		{in: `4 >= 4`, out: `true`},
		{in: `4 < 6`, out: `true`},
		{in: `4 <= 4`, out: `true`},
		{in: `4 AND 5`, out: `4 AND 5`},

		// Boolean literals.
		{in: `true AND false`, out: `false`},
		{in: `true OR false`, out: `true`},
		{in: `true OR (foo = bar AND 1 > 2)`, out: `true`},
		{in: `(foo = bar AND 1 > 2) OR true`, out: `true`},
		{in: `false OR (foo = bar AND 1 > 2)`, out: `false`},
		{in: `(foo = bar AND 1 > 2) OR false`, out: `false`},
		{in: `true = false`, out: `false`},
		{in: `true <> false`, out: `true`},
		{in: `true + false`, out: `true + false`},

		// Time literals with now().
		{in: `now() + 2h`, out: `'2000-01-01T02:00:00Z'`, data: map[string]interface{}{"now()": now}},
		{in: `now() / 2h`, out: `'2000-01-01T00:00:00Z' / 2h`, data: map[string]interface{}{"now()": now}},
		{in: `4µ + now()`, out: `'2000-01-01T00:00:00.000004Z'`, data: map[string]interface{}{"now()": now}},
		{in: `now() + 2000000000`, out: `'2000-01-01T00:00:02Z'`, data: map[string]interface{}{"now()": now}},
		{in: `2000000000 + now()`, out: `'2000-01-01T00:00:02Z'`, data: map[string]interface{}{"now()": now}},
		{in: `now() - 2000000000`, out: `'1999-12-31T23:59:58Z'`, data: map[string]interface{}{"now()": now}},
		{in: `now() = now()`, out: `true`, data: map[string]interface{}{"now()": now}},
		{in: `now() <> now()`, out: `false`, data: map[string]interface{}{"now()": now}},
		{in: `now() < now() + 1h`, out: `true`, data: map[string]interface{}{"now()": now}},
		{in: `now() <= now() + 1h`, out: `true`, data: map[string]interface{}{"now()": now}},
		{in: `now() >= now() - 1h`, out: `true`, data: map[string]interface{}{"now()": now}},
		{in: `now() > now() - 1h`, out: `true`, data: map[string]interface{}{"now()": now}},
		{in: `now() - (now() - 60s)`, out: `1m`, data: map[string]interface{}{"now()": now}},
		{in: `now() AND now()`, out: `'2000-01-01T00:00:00Z' AND '2000-01-01T00:00:00Z'`, data: map[string]interface{}{"now()": now}},
		{in: `now()`, out: `now()`},
		{in: `946684800000000000 + 2h`, out: `'2000-01-01T02:00:00Z'`},

		// Time literals.
		{in: `'2000-01-01T00:00:00Z' + 2h`, out: `'2000-01-01T02:00:00Z'`},
		{in: `'2000-01-01T00:00:00Z' / 2h`, out: `'2000-01-01T00:00:00Z' / 2h`},
		{in: `4µ + '2000-01-01T00:00:00Z'`, out: `'2000-01-01T00:00:00.000004Z'`},
		{in: `'2000-01-01T00:00:00Z' + 2000000000`, out: `'2000-01-01T00:00:02Z'`},
		{in: `2000000000 + '2000-01-01T00:00:00Z'`, out: `'2000-01-01T00:00:02Z'`},
		{in: `'2000-01-01T00:00:00Z' - 2000000000`, out: `'1999-12-31T23:59:58Z'`},
		{in: `'2000-01-01T00:00:00Z' = '2000-01-01T00:00:00Z'`, out: `true`},
		{in: `'2000-01-01T00:00:00.000000000Z' = '2000-01-01T00:00:00Z'`, out: `true`},
		{in: `'2000-01-01T00:00:00Z' <> '2000-01-01T00:00:00Z'`, out: `false`},
		{in: `'2000-01-01T00:00:00.000000000Z' <> '2000-01-01T00:00:00Z'`, out: `false`},
		{in: `'2000-01-01T00:00:00Z' < '2000-01-01T00:00:00Z' + 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00.000000000Z' < '2000-01-01T00:00:00Z' + 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00Z' <= '2000-01-01T00:00:00Z' + 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00.000000000Z' <= '2000-01-01T00:00:00Z' + 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00Z' > '2000-01-01T00:00:00Z' - 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00.000000000Z' > '2000-01-01T00:00:00Z' - 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00Z' >= '2000-01-01T00:00:00Z' - 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00.000000000Z' >= '2000-01-01T00:00:00Z' - 1h`, out: `true`},
		{in: `'2000-01-01T00:00:00Z' - ('2000-01-01T00:00:00Z' - 60s)`, out: `1m`},
		{in: `'2000-01-01T00:00:00Z' AND '2000-01-01T00:00:00Z'`, out: `'2000-01-01T00:00:00Z' AND '2000-01-01T00:00:00Z'`},

		// Duration literals.
		{in: `10m + 1h - 60s`, out: `69m`},
		{in: `(10m / 2) * 5`, out: `25m`},
		{in: `60s = 1m`, out: `true`},
		{in: `60s <> 1m`, out: `false`},
		{in: `60s < 1h`, out: `true`},
		{in: `60s <= 1h`, out: `true`},
		{in: `60s > 12s`, out: `true`},
		{in: `60s >= 1m`, out: `true`},
		{in: `60s AND 1m`, out: `1m AND 1m`},
		{in: `60m / 0`, out: `0s`},
		{in: `60m + 50`, out: `1h + 50`},

		// String literals.
		{in: `'foo' + 'bar'`, out: `'foobar'`},

		// Variable references.
		{in: `foo`, out: `'bar'`, data: map[string]interface{}{"foo": "bar"}},
		{in: `foo = 'bar'`, out: `true`, data: map[string]interface{}{"foo": "bar"}},
		{in: `foo = 'bar'`, out: `false`, data: map[string]interface{}{"foo": nil}},
		{in: `foo <> 'bar'`, out: `false`, data: map[string]interface{}{"foo": nil}},
	} {
		// Fold expression.
		expr := influxql.Reduce(MustParseExpr(tt.in), tt.data)

		// Compare with expected output.
//.........这里部分代码省略.........

// mergeSeriesFilters merges two sets of filter expressions and culls series IDs.
func mergeSeriesFilters(op influxql.Token, ids SeriesIDs, lfilters, rfilters FilterExprs) (SeriesIDs, FilterExprs) {
	// Create a map to hold the final set of series filter expressions.
	filters := make(map[uint64]influxql.Expr, 0)
	// Resulting list of series IDs
	var series SeriesIDs

	// Combining logic:
	// +==========+==========+==========+=======================+=======================+
	// | operator |   LHS    |   RHS    |   intermediate expr   |     reduced filter    |
	// +==========+==========+==========+=======================+=======================+
	// |          | <nil>    | <r-expr> | false OR <r-expr>     | <r-expr>              |
	// |          |----------+----------+-----------------------+-----------------------+
	// | OR       | <l-expr> | <nil>    | <l-expr> OR false     | <l-expr>              |
	// |          |----------+----------+-----------------------+-----------------------+
	// |          | <nil>    | <nil>    | false OR false        | false                 |
	// |          |----------+----------+-----------------------+-----------------------+
	// |          | <l-expr> | <r-expr> | <l-expr> OR <r-expr>  | <l-expr> OR <r-expr>  |
	// +----------+----------+----------+-----------------------+-----------------------+
	// |          | <nil>    | <r-expr> | false AND <r-expr>    | false*                |
	// |          |----------+----------+-----------------------+-----------------------+
	// | AND      | <l-expr> | <nil>    | <l-expr> AND false    | false                 |
	// |          |----------+----------+-----------------------+-----------------------+
	// |          | <nil>    | <nil>    | false AND false       | false                 |
	// |          |----------+----------+-----------------------+-----------------------+
	// |          | <l-expr> | <r-expr> | <l-expr> AND <r-expr> | <l-expr> AND <r-expr> |
	// +----------+----------+----------+-----------------------+-----------------------+
	// *literal false filters and series IDs should be excluded from the results

	for _, id := range ids {
		// Get LHS and RHS filter expressions for this series ID.
		lfilter, rfilter := lfilters[id], rfilters[id]

		// Set filter to false if either LHS or RHS expressions were nil.
		if lfilter == nil {
			lfilter = &influxql.BooleanLiteral{Val: false}
		}
		if rfilter == nil {
			rfilter = &influxql.BooleanLiteral{Val: false}
		}

		// Create the intermediate filter expression for this series ID.
		be := &influxql.BinaryExpr{
			Op:  op,
			LHS: lfilter,
			RHS: rfilter,
		}

		// Reduce the intermediate expression.
		expr := influxql.Reduce(be, nil)

		// If the expression reduced to false, exclude this series ID and filter.
		if b, ok := expr.(*influxql.BooleanLiteral); ok && !b.Val {
			continue
		}

		// Store the series ID and merged filter in the final results.
		if expr != nil {
			filters[id] = expr
		}
		series = append(series, id)
	}
	return series, filters
}

func (e *StatementExecutor) createIterators(stmt *influxql.SelectStatement, ctx *influxql.ExecutionContext) ([]influxql.Iterator, *influxql.SelectStatement, error) {
	// It is important to "stamp" this time so that everywhere we evaluate `now()` in the statement is EXACTLY the same `now`
	now := time.Now().UTC()
	opt := influxql.SelectOptions{
		InterruptCh: ctx.InterruptCh,
		NodeID:      ctx.ExecutionOptions.NodeID,
		MaxSeriesN:  e.MaxSelectSeriesN,
	}

	// Replace instances of "now()" with the current time, and check the resultant times.
	nowValuer := influxql.NowValuer{Now: now}
	stmt.Condition = influxql.Reduce(stmt.Condition, &nowValuer)
	// Replace instances of "now()" with the current time in the dimensions.
	for _, d := range stmt.Dimensions {
		d.Expr = influxql.Reduce(d.Expr, &nowValuer)
	}

	var err error
	opt.MinTime, opt.MaxTime, err = influxql.TimeRange(stmt.Condition)
	if err != nil {
		return nil, stmt, err
	}

	if opt.MaxTime.IsZero() {
		// In the case that we're executing a meta query where the user cannot
		// specify a time condition, then we expand the default max time
		// to the maximum possible value, to ensure that data where all points
		// are in the future are returned.
		if influxql.Sources(stmt.Sources).HasSystemSource() {
			opt.MaxTime = time.Unix(0, influxql.MaxTime).UTC()
		} else {
			if interval, err := stmt.GroupByInterval(); err != nil {
				return nil, stmt, err
			} else if interval > 0 {
				opt.MaxTime = now
			} else {
				opt.MaxTime = time.Unix(0, influxql.MaxTime).UTC()
			}
		}
	}
	if opt.MinTime.IsZero() {
		opt.MinTime = time.Unix(0, influxql.MinTime).UTC()
	}

	// Convert DISTINCT into a call.
	stmt.RewriteDistinct()

	// Remove "time" from fields list.
	stmt.RewriteTimeFields()

	// Rewrite any regex conditions that could make use of the index.
	stmt.RewriteRegexConditions()

	// Create an iterator creator based on the shards in the cluster.
	ic, err := e.iteratorCreator(stmt, &opt)
	if err != nil {
		return nil, stmt, err
	}

	// Expand regex sources to their actual source names.
	if stmt.Sources.HasRegex() {
		sources, err := ic.ExpandSources(stmt.Sources)
		if err != nil {
			return nil, stmt, err
		}
		stmt.Sources = sources
	}

	// Rewrite wildcards, if any exist.
	tmp, err := stmt.RewriteFields(ic)
	if err != nil {
		return nil, stmt, err
	}
	stmt = tmp

	if e.MaxSelectBucketsN > 0 && !stmt.IsRawQuery {
		interval, err := stmt.GroupByInterval()
		if err != nil {
			return nil, stmt, err
		}

		if interval > 0 {
			// Determine the start and end time matched to the interval (may not match the actual times).
			min := opt.MinTime.Truncate(interval)
			max := opt.MaxTime.Truncate(interval).Add(interval)

			// Determine the number of buckets by finding the time span and dividing by the interval.
			buckets := int64(max.Sub(min)) / int64(interval)
			if int(buckets) > e.MaxSelectBucketsN {
				return nil, stmt, fmt.Errorf("max-select-buckets limit exceeded: (%d/%d)", buckets, e.MaxSelectBucketsN)
			}
		}
	}

	// Create a set of iterators from a selection.
	itrs, err := influxql.Select(stmt, ic, &opt)
	if err != nil {
		return nil, stmt, err
	}

//.........这里部分代码省略.........

func (s *Store) TagValues(database string, cond influxql.Expr) ([]TagValues, error) {
	if cond == nil {
		return nil, errors.New("a condition is required")
	}

	dbi := s.DatabaseIndex(database)
	if dbi == nil {
		return nil, nil
	}

	measurementExpr := influxql.CloneExpr(cond)
	measurementExpr = influxql.Reduce(influxql.RewriteExpr(measurementExpr, func(e influxql.Expr) influxql.Expr {
		switch e := e.(type) {
		case *influxql.BinaryExpr:
			switch e.Op {
			case influxql.EQ, influxql.NEQ, influxql.EQREGEX, influxql.NEQREGEX:
				tag, ok := e.LHS.(*influxql.VarRef)
				if !ok || tag.Val != "_name" {
					return nil
				}
			}
		}
		return e
	}), nil)

	mms, ok, err := dbi.MeasurementsByExpr(measurementExpr)
	if err != nil {
		return nil, err
	} else if !ok {
		mms = dbi.Measurements()
		sort.Sort(mms)
	}

	// If there are no measurements, return immediately.
	if len(mms) == 0 {
		return nil, nil
	}

	filterExpr := influxql.CloneExpr(cond)
	filterExpr = influxql.Reduce(influxql.RewriteExpr(filterExpr, func(e influxql.Expr) influxql.Expr {
		switch e := e.(type) {
		case *influxql.BinaryExpr:
			switch e.Op {
			case influxql.EQ, influxql.NEQ, influxql.EQREGEX, influxql.NEQREGEX:
				tag, ok := e.LHS.(*influxql.VarRef)
				if !ok || strings.HasPrefix(tag.Val, "_") {
					return nil
				}
			}
		}
		return e
	}), nil)

	tagValues := make([]TagValues, len(mms))
	for i, mm := range mms {
		tagValues[i].Measurement = mm.Name

		ids, err := mm.SeriesIDsAllOrByExpr(filterExpr)
		if err != nil {
			return nil, err
		}
		ss := mm.SeriesByIDSlice(ids)

		// Determine a list of keys from condition.
		keySet, ok, err := mm.TagKeysByExpr(cond)
		if err != nil {
			return nil, err
		}

		// Loop over all keys for each series.
		m := make(map[KeyValue]struct{}, len(ss))
		for _, series := range ss {
			for key, value := range series.Tags {
				if !ok {
					// nop
				} else if _, exists := keySet[key]; !exists {
					continue
				}
				m[KeyValue{key, value}] = struct{}{}
			}
		}

		// Return an empty slice if there are no key/value matches.
		if len(m) == 0 {
			continue
		}

		// Sort key/value set.
		a := make([]KeyValue, 0, len(m))
		for kv := range m {
			a = append(a, kv)
		}
		sort.Sort(KeyValues(a))
		tagValues[i].Values = a
	}

	return tagValues, nil
}

func (e *StatementExecutor) executeShowTagValues(stmt *influxql.SelectStatement, ctx *influxql.ExecutionContext, store LocalTSDBStore) error {
	if stmt.Condition == nil {
		return errors.New("a condition is required")
	}

	source := stmt.Sources[0].(*influxql.Measurement)
	index := store.DatabaseIndex(source.Database)
	if index == nil {
		ctx.Results <- &influxql.Result{StatementID: ctx.StatementID, Series: make([]*models.Row, 0)}
		return nil
	}

	measurementExpr := influxql.CloneExpr(stmt.Condition)
	measurementExpr = influxql.Reduce(influxql.RewriteExpr(measurementExpr, func(e influxql.Expr) influxql.Expr {
		switch e := e.(type) {
		case *influxql.BinaryExpr:
			switch e.Op {
			case influxql.EQ, influxql.NEQ, influxql.EQREGEX, influxql.NEQREGEX:
				tag, ok := e.LHS.(*influxql.VarRef)
				if !ok || tag.Val != "_name" {
					return nil
				}
			}
		}
		return e
	}), nil)

	mms, ok, err := index.MeasurementsByExpr(measurementExpr)
	if err != nil {
		return err
	} else if !ok {
		mms = index.Measurements()
		sort.Sort(mms)
	}

	// If there are no measurements, return immediately.
	if len(mms) == 0 {
		ctx.Results <- &influxql.Result{StatementID: ctx.StatementID, Series: make([]*models.Row, 0)}
		return nil
	}

	filterExpr := influxql.CloneExpr(stmt.Condition)
	filterExpr = influxql.Reduce(influxql.RewriteExpr(filterExpr, func(e influxql.Expr) influxql.Expr {
		switch e := e.(type) {
		case *influxql.BinaryExpr:
			switch e.Op {
			case influxql.EQ, influxql.NEQ, influxql.EQREGEX, influxql.NEQREGEX:
				tag, ok := e.LHS.(*influxql.VarRef)
				if !ok || strings.HasPrefix(tag.Val, "_") {
					return nil
				}
			}
		}
		return e
	}), nil)

	var emitted bool
	columns := stmt.ColumnNames()
	for _, mm := range mms {
		ids, err := mm.SeriesIDsAllOrByExpr(filterExpr)
		if err != nil {
			return err
		}
		ss := mm.SeriesByIDSlice(ids)

		// Determine a list of keys from condition.
		keySet, ok, err := mm.TagKeysByExpr(stmt.Condition)
		if err != nil {
			return err
		}

		// Loop over all keys for each series.
		m := make(map[keyValue]struct{}, len(ss))
		for _, series := range ss {
			for key, value := range series.Tags {
				if !ok {
					// nop
				} else if _, exists := keySet[key]; !exists {
					continue
				}
				m[keyValue{key, value}] = struct{}{}
			}
		}

		// Move to next series if no key/values match.
		if len(m) == 0 {
			continue
		}

		// Sort key/value set.
		a := make([]keyValue, 0, len(m))
		for kv := range m {
			a = append(a, kv)
		}
		sort.Sort(keyValues(a))

		// Convert to result values.
		slab := make([]interface{}, len(a)*2)
		values := make([][]interface{}, len(a))
		for i, elem := range a {
//.........这里部分代码省略.........

func (e *StatementExecutor) executeSelectStatement(stmt *influxql.SelectStatement, ctx *influxql.ExecutionContext) error {
	// Handle SHOW TAG VALUES separately so it can be optimized.
	// https://github.com/influxdata/influxdb/issues/6233
	if source, ok := stmt.Sources[0].(*influxql.Measurement); ok && source.Name == "_tags" {
		// Use the optimized version only if we have direct access to the database.
		if store, ok := e.TSDBStore.(LocalTSDBStore); ok {
			return e.executeShowTagValues(stmt, ctx, store)
		}
	}

	// It is important to "stamp" this time so that everywhere we evaluate `now()` in the statement is EXACTLY the same `now`
	now := time.Now().UTC()
	opt := influxql.SelectOptions{InterruptCh: ctx.InterruptCh}

	// Replace instances of "now()" with the current time, and check the resultant times.
	nowValuer := influxql.NowValuer{Now: now}
	stmt.Condition = influxql.Reduce(stmt.Condition, &nowValuer)
	// Replace instances of "now()" with the current time in the dimensions.
	for _, d := range stmt.Dimensions {
		d.Expr = influxql.Reduce(d.Expr, &nowValuer)
	}

	var err error
	opt.MinTime, opt.MaxTime, err = influxql.TimeRange(stmt.Condition)
	if err != nil {
		return err
	}

	if opt.MaxTime.IsZero() {
		// In the case that we're executing a meta query where the user cannot
		// specify a time condition, then we expand the default max time
		// to the maximum possible value, to ensure that data where all points
		// are in the future are returned.
		if influxql.Sources(stmt.Sources).HasSystemSource() {
			opt.MaxTime = time.Unix(0, influxql.MaxTime).UTC()
		} else {
			opt.MaxTime = now
		}
	}
	if opt.MinTime.IsZero() {
		opt.MinTime = time.Unix(0, 0)
	}

	// Convert DISTINCT into a call.
	stmt.RewriteDistinct()

	// Remove "time" from fields list.
	stmt.RewriteTimeFields()

	// Create an iterator creator based on the shards in the cluster.
	ic, err := e.iteratorCreator(stmt, &opt)
	if err != nil {
		return err
	}

	// Expand regex sources to their actual source names.
	if stmt.Sources.HasRegex() {
		sources, err := ic.ExpandSources(stmt.Sources)
		if err != nil {
			return err
		}
		stmt.Sources = sources
	}

	// Rewrite wildcards, if any exist.
	tmp, err := stmt.RewriteFields(ic)
	if err != nil {
		return err
	}
	stmt = tmp

	if e.MaxSelectBucketsN > 0 && !stmt.IsRawQuery {
		interval, err := stmt.GroupByInterval()
		if err != nil {
			return err
		}

		if interval > 0 {
			// Determine the start and end time matched to the interval (may not match the actual times).
			min := opt.MinTime.Truncate(interval)
			max := opt.MaxTime.Truncate(interval).Add(interval)

			// Determine the number of buckets by finding the time span and dividing by the interval.
			buckets := int64(max.Sub(min)) / int64(interval)
			if int(buckets) > e.MaxSelectBucketsN {
				return fmt.Errorf("max select bucket count exceeded: %d buckets", buckets)
			}
		}
	}

	// Create a set of iterators from a selection.
	itrs, err := influxql.Select(stmt, ic, &opt)
	if err != nil {
		return err
	}

	if e.MaxSelectPointN > 0 {
		monitor := influxql.PointLimitMonitor(itrs, influxql.DefaultStatsInterval, e.MaxSelectPointN)
		ctx.Query.Monitor(monitor)
	}
//.........这里部分代码省略.........

// NewTagValuesIterator returns a new instance of TagValuesIterator.
func NewTagValuesIterator(sh *Shard, opt influxql.IteratorOptions) (influxql.Iterator, error) {
	if opt.Condition == nil {
		return nil, errors.New("a condition is required")
	}

	measurementExpr := influxql.CloneExpr(opt.Condition)
	measurementExpr = influxql.Reduce(influxql.RewriteExpr(measurementExpr, func(e influxql.Expr) influxql.Expr {
		switch e := e.(type) {
		case *influxql.BinaryExpr:
			switch e.Op {
			case influxql.EQ, influxql.NEQ, influxql.EQREGEX, influxql.NEQREGEX:
				tag, ok := e.LHS.(*influxql.VarRef)
				if !ok || tag.Val != "_name" {
					return nil
				}
			}
		}
		return e
	}), nil)

	mms, ok, err := sh.index.measurementsByExpr(measurementExpr)
	if err != nil {
		return nil, err
	} else if !ok {
		mms = sh.index.Measurements()
		sort.Sort(mms)
	}

	// If there are no measurements, return immediately.
	if len(mms) == 0 {
		return &tagValuesIterator{}, nil
	}

	filterExpr := influxql.CloneExpr(opt.Condition)
	filterExpr = influxql.Reduce(influxql.RewriteExpr(filterExpr, func(e influxql.Expr) influxql.Expr {
		switch e := e.(type) {
		case *influxql.BinaryExpr:
			switch e.Op {
			case influxql.EQ, influxql.NEQ, influxql.EQREGEX, influxql.NEQREGEX:
				tag, ok := e.LHS.(*influxql.VarRef)
				if !ok || strings.HasPrefix(tag.Val, "_") {
					return nil
				}
			}
		}
		return e
	}), nil)

	var series []*Series
	keys := newStringSet()
	for _, mm := range mms {
		ss, ok, err := mm.TagKeysByExpr(opt.Condition)
		if err != nil {
			return nil, err
		} else if !ok {
			keys.add(mm.TagKeys()...)
		} else {
			keys = keys.union(ss)
		}

		ids, err := mm.seriesIDsAllOrByExpr(filterExpr)
		if err != nil {
			return nil, err
		}

		for _, id := range ids {
			series = append(series, mm.SeriesByID(id))
		}
	}

	return &tagValuesIterator{
		series: series,
		keys:   keys.list(),
		fields: influxql.VarRefs(opt.Aux).Strings(),
	}, nil
}

func (e *StatementExecutor) executeSelectStatement(stmt *influxql.SelectStatement, ctx *influxql.ExecutionContext) error {
	// It is important to "stamp" this time so that everywhere we evaluate `now()` in the statement is EXACTLY the same `now`
	now := time.Now().UTC()
	opt := influxql.SelectOptions{InterruptCh: ctx.InterruptCh}

	// Replace instances of "now()" with the current time, and check the resultant times.
	stmt.Condition = influxql.Reduce(stmt.Condition, &influxql.NowValuer{Now: now})
	var err error
	opt.MinTime, opt.MaxTime, err = influxql.TimeRange(stmt.Condition)
	if err != nil {
		return err
	}

	if opt.MaxTime.IsZero() {
		opt.MaxTime = now
	}
	if opt.MinTime.IsZero() {
		opt.MinTime = time.Unix(0, 0)
	}

	// Convert DISTINCT into a call.
	stmt.RewriteDistinct()

	// Remove "time" from fields list.
	stmt.RewriteTimeFields()

	// Create an iterator creator based on the shards in the cluster.
	ic, err := e.iteratorCreator(stmt, &opt)
	if err != nil {
		return err
	}

	// Expand regex sources to their actual source names.
	if stmt.Sources.HasRegex() {
		sources, err := ic.ExpandSources(stmt.Sources)
		if err != nil {
			return err
		}
		stmt.Sources = sources
	}

	// Rewrite wildcards, if any exist.
	tmp, err := stmt.RewriteWildcards(ic)
	if err != nil {
		return err
	}
	stmt = tmp

	if e.MaxSelectBucketsN > 0 && !stmt.IsRawQuery {
		interval, err := stmt.GroupByInterval()
		if err != nil {
			return err
		}

		if interval > 0 {
			// Determine the start and end time matched to the interval (may not match the actual times).
			min := opt.MinTime.Truncate(interval)
			max := opt.MaxTime.Truncate(interval).Add(interval)

			// Determine the number of buckets by finding the time span and dividing by the interval.
			buckets := int64(max.Sub(min)) / int64(interval)
			if int(buckets) > e.MaxSelectBucketsN {
				return fmt.Errorf("max select bucket count exceeded: %d buckets", buckets)
			}
		}
	}

	// Create a set of iterators from a selection.
	itrs, err := influxql.Select(stmt, ic, &opt)
	if err != nil {
		return err
	}

	if e.MaxSelectPointN > 0 {
		monitor := influxql.PointLimitMonitor(itrs, influxql.DefaultStatsInterval, e.MaxSelectPointN)
		ctx.Query.Monitor(monitor)
	}

	// Generate a row emitter from the iterator set.
	em := influxql.NewEmitter(itrs, stmt.TimeAscending(), ctx.ChunkSize)
	em.Columns = stmt.ColumnNames()
	em.OmitTime = stmt.OmitTime
	defer em.Close()

	// Calculate initial stats across all iterators.
	stats := influxql.Iterators(itrs).Stats()
	if e.MaxSelectSeriesN > 0 && stats.SeriesN > e.MaxSelectSeriesN {
		return fmt.Errorf("max select series count exceeded: %d series", stats.SeriesN)
	}

	// Emit rows to the results channel.
	var writeN int64
	var emitted bool
	for {
		row := em.Emit()
		if row == nil {
			// Check if the query was interrupted while emitting.
			select {
			case <-ctx.InterruptCh:
				return influxql.ErrQueryInterrupted
//.........这里部分代码省略.........

func (e *QueryExecutor) executeSelectStatement(stmt *influxql.SelectStatement, chunkSize, statementID int, results chan *influxql.Result, closing <-chan struct{}) error {
	// It is important to "stamp" this time so that everywhere we evaluate `now()` in the statement is EXACTLY the same `now`
	now := time.Now().UTC()
	opt := influxql.SelectOptions{}

	// Replace instances of "now()" with the current time, and check the resultant times.
	stmt.Condition = influxql.Reduce(stmt.Condition, &influxql.NowValuer{Now: now})
	opt.MinTime, opt.MaxTime = influxql.TimeRange(stmt.Condition)
	if opt.MaxTime.IsZero() {
		opt.MaxTime = now
	}
	if opt.MinTime.IsZero() {
		opt.MinTime = time.Unix(0, 0)
	}

	// Convert DISTINCT into a call.
	stmt.RewriteDistinct()

	// Remove "time" from fields list.
	stmt.RewriteTimeFields()

	// Create an iterator creator based on the shards in the cluster.
	ic, err := e.iteratorCreator(stmt, &opt)
	if err != nil {
		return err
	}

	// Expand regex sources to their actual source names.
	if stmt.Sources.HasRegex() {
		sources, err := ic.ExpandSources(stmt.Sources)
		if err != nil {
			return err
		}
		stmt.Sources = sources
	}

	// Rewrite wildcards, if any exist.
	tmp, err := stmt.RewriteWildcards(ic)
	if err != nil {
		return err
	}
	stmt = tmp

	// Create a set of iterators from a selection.
	itrs, err := influxql.Select(stmt, ic, &opt)
	if err != nil {
		return err
	}

	// Generate a row emitter from the iterator set.
	em := influxql.NewEmitter(itrs, stmt.TimeAscending())
	em.Columns = stmt.ColumnNames()
	em.OmitTime = stmt.OmitTime
	defer em.Close()

	// Emit rows to the results channel.
	var writeN int64
	var emitted bool
	for {
		row := em.Emit()
		if row == nil {
			break
		}

		result := &influxql.Result{
			StatementID: statementID,
			Series:      []*models.Row{row},
		}

		// Write points back into system for INTO statements.
		if stmt.Target != nil {
			if err := e.writeInto(stmt, row); err != nil {
				return err
			}
			writeN += int64(len(row.Values))
			continue
		}

		// Send results or exit if closing.
		select {
		case <-closing:
			return nil
		case results <- result:
		}

		emitted = true
	}

	// Emit write count if an INTO statement.
	if stmt.Target != nil {
		results <- &influxql.Result{
			StatementID: statementID,
			Series: []*models.Row{{
				Name:    "result",
				Columns: []string{"time", "written"},
				Values:  [][]interface{}{{time.Unix(0, 0).UTC(), writeN}},
			}},
		}
		return nil
	}
//.........这里部分代码省略.........