Convert SHOW FIELD KEYS to the new query engine

Fixes #5579.

cluster/query_executor.go

@@ -168,8 +168,6 @@ func (e *QueryExecutor) executeQuery(query *influxql.Query, database string, chu
 			rows, err = e.executeShowDatabasesStatement(stmt)
 		case *influxql.ShowDiagnosticsStatement:
 			rows, err = e.executeShowDiagnosticsStatement(stmt)
-		case *influxql.ShowFieldKeysStatement:
-			rows, err = e.executeShowFieldKeysStatement(stmt, database)
 		case *influxql.ShowGrantsForUserStatement:
 			rows, err = e.executeShowGrantsForUserStatement(stmt)
 		case *influxql.ShowRetentionPoliciesStatement:

influxql/statement_rewriter.go

@@ -7,6 +7,8 @@ import (
 // RewriteStatement rewrites stmt into a new statement, if applicable.
 func RewriteStatement(stmt Statement) (Statement, error) {
 	switch stmt := stmt.(type) {
+	case *ShowFieldKeysStatement:
+		return rewriteShowFieldKeysStatement(stmt)
 	case *ShowMeasurementsStatement:
 		return rewriteShowMeasurementsStatement(stmt)
 	case *ShowTagKeysStatement:
@@ -16,6 +18,42 @@ func RewriteStatement(stmt Statement) (Statement, error) {
 	}
 }
 
+func rewriteShowFieldKeysStatement(stmt *ShowFieldKeysStatement) (Statement, error) {
+	var condition Expr
+	if len(stmt.Sources) > 0 {
+		if source, ok := stmt.Sources[0].(*Measurement); ok {
+			if source.Regex != nil {
+				condition = &BinaryExpr{
+					Op:  EQREGEX,
+					LHS: &VarRef{Val: "name"},
+					RHS: &RegexLiteral{Val: source.Regex.Val},
+				}
+			} else if source.Name != "" {
+				condition = &BinaryExpr{
+					Op:  EQ,
+					LHS: &VarRef{Val: "name"},
+					RHS: &StringLiteral{Val: source.Name},
+				}
+			}
+		}
+	}
+
+	return &SelectStatement{
+		Fields: Fields([]*Field{
+			{Expr: &VarRef{Val: "fieldKey"}},
+		}),
+		Sources: Sources([]Source{
+			&Measurement{Name: "_fieldKeys"},
+		}),
+		Condition:  condition,
+		Offset:     stmt.Offset,
+		Limit:      stmt.Limit,
+		SortFields: stmt.SortFields,
+		OmitTime:   true,
+		Dedupe:     true,
+	}, nil
+}
+
 func rewriteShowMeasurementsStatement(stmt *ShowMeasurementsStatement) (Statement, error) {
 	// Check for time in WHERE clause (not supported).
 	if HasTimeExpr(stmt.Condition) {

influxql/statement_rewriter_test.go

@@ -0,0 +1,81 @@
+package influxql_test
+
+import (
+	"testing"
+
+	"github.com/influxdata/influxdb/influxql"
+)
+
+func TestRewriteStatement(t *testing.T) {
+	tests := []struct {
+		stmt string
+		s    string
+	}{
+		{
+			stmt: `SHOW FIELD KEYS`,
+			s:    `SELECT fieldKey FROM _fieldKeys`,
+		},
+		{
+			stmt: `SHOW FIELD KEYS FROM cpu`,
+			s:    `SELECT fieldKey FROM _fieldKeys WHERE "name" = 'cpu'`,
+		},
+		{
+			stmt: `SHOW FIELD KEYS FROM /c.*/`,
+			s:    `SELECT fieldKey FROM _fieldKeys WHERE "name" =~ /c.*/`,
+		},
+		{
+			stmt: `SHOW MEASUREMENTS`,
+			s:    `SELECT "name" FROM _measurements`,
+		},
+		{
+			stmt: `SHOW MEASUREMENTS WITH MEASUREMENT = cpu`,
+			s:    `SELECT "name" FROM _measurements WHERE "name" = 'cpu'`,
+		},
+		{
+			stmt: `SHOW MEASUREMENTS WITH MEASUREMENT =~ /c.*/`,
+			s:    `SELECT "name" FROM _measurements WHERE "name" =~ /c.*/`,
+		},
+		{
+			stmt: `SHOW MEASUREMENTS WHERE region = 'uswest'`,
+			s:    `SELECT "name" FROM _measurements WHERE region = 'uswest'`,
+		},
+		{
+			stmt: `SHOW MEASUREMENTS WITH MEASUREMENT = cpu WHERE region = 'uswest'`,
+			s:    `SELECT "name" FROM _measurements WHERE "name" = 'cpu' AND region = 'uswest'`,
+		},
+		{
+			stmt: `SHOW TAG KEYS`,
+			s:    `SELECT tagKey FROM _tagKeys`,
+		},
+		{
+			stmt: `SHOW TAG KEYS FROM cpu`,
+			s:    `SELECT tagKey FROM _tagKeys WHERE "name" = 'cpu'`,
+		},
+		{
+			stmt: `SHOW TAG KEYS FROM /c.*/`,
+			s:    `SELECT tagKey FROM _tagKeys WHERE "name" =~ /c.*/`,
+		},
+		{
+			stmt: `SHOW TAG KEYS FROM cpu WHERE region = 'uswest'`,
+			s:    `SELECT tagKey FROM _tagKeys WHERE "name" = 'cpu' AND region = 'uswest'`,
+		},
+		{
+			stmt: `SELECT value FROM cpu`,
+			s:    `SELECT value FROM cpu`,
+		},
+	}
+
+	for _, test := range tests {
+		stmt, err := influxql.ParseStatement(test.stmt)
+		if err != nil {
+			t.Errorf("error parsing statement: %s", err)
+		} else {
+			stmt, err = influxql.RewriteStatement(stmt)
+			if err != nil {
+				t.Errorf("error rewriting statement: %s", err)
+			} else if s := stmt.String(); s != test.s {
+				t.Errorf("error rendering string. expected %s, actual: %s", test.s, s)
+			}
+		}
+	}
+}

tsdb/shard.go

@@ -420,6 +420,8 @@ func (s *Shard) createSystemIterator(opt influxql.IteratorOptions) (influxql.Ite
 
 	m := opt.Sources[0].(*influxql.Measurement)
 	switch m.Name {
+	case "_fieldKeys":
+		return NewFieldKeysIterator(s, opt)
 	case "_measurements":
 		return NewMeasurementIterator(s, opt)
 	case "_tagKeys":
@@ -824,6 +826,15 @@ func (ic *shardIteratorCreator) SeriesKeys(opt influxql.IteratorOptions) (influx
 	return ic.sh.SeriesKeys(opt)
 }
 
+func NewFieldKeysIterator(sh *Shard, opt influxql.IteratorOptions) (influxql.Iterator, error) {
+	fn := func(m *Measurement) []string {
+		keys := m.FieldNames()
+		sort.Strings(keys)
+		return keys
+	}
+	return newMeasurementKeysIterator(sh, fn, opt)
+}
+
 // MeasurementIterator represents a string iterator that emits all measurement names in a shard.
 type MeasurementIterator struct {
 	mms    Measurements
@@ -872,18 +883,19 @@ func (itr *MeasurementIterator) Next() *influxql.FloatPoint {
 	}
 }
 
-// TagKeysIterator represents a string iterator that emits all tag keys in a shard.
-type TagKeysIterator struct {
-	mms Measurements // remaining measurements
-	buf struct {
-		mm   *Measurement // current measurement
-		keys []string     // current measurement's keys
+// NewTagKeysIterator returns a new instance of TagKeysIterator.
+func NewTagKeysIterator(sh *Shard, opt influxql.IteratorOptions) (influxql.Iterator, error) {
+	fn := func(m *Measurement) []string {
+		return m.TagKeys()
 	}
+	return newMeasurementKeysIterator(sh, fn, opt)
 }
 
-// NewTagKeysIterator returns a new instance of TagKeysIterator.
-func NewTagKeysIterator(sh *Shard, opt influxql.IteratorOptions) (*TagKeysIterator, error) {
-	itr := &TagKeysIterator{}
+// measurementKeyFunc is the function called by measurementKeysIterator.
+type measurementKeyFunc func(m *Measurement) []string
+
+func newMeasurementKeysIterator(sh *Shard, fn measurementKeyFunc, opt influxql.IteratorOptions) (*measurementKeysIterator, error) {
+	itr := &measurementKeysIterator{fn: fn}
 
 	// Retrieve measurements from shard. Filter if condition specified.
 	if opt.Condition == nil {
@@ -902,11 +914,21 @@ func NewTagKeysIterator(sh *Shard, opt influxql.IteratorOptions) (*TagKeysIterat
 	return itr, nil
 }
 
+// measurementKeysIterator iterates over measurements and gets keys from each measurement.
+type measurementKeysIterator struct {
+	mms Measurements // remaining measurements
+	buf struct {
+		mm   *Measurement // current measurement
+		keys []string     // current measurement's keys
+	}
+	fn measurementKeyFunc
+}
+
 // Close closes the iterator.
-func (itr *TagKeysIterator) Close() error { return nil }
+func (itr *measurementKeysIterator) Close() error { return nil }
 
 // Next emits the next tag key name.
-func (itr *TagKeysIterator) Next() *influxql.FloatPoint {
+func (itr *measurementKeysIterator) Next() *influxql.FloatPoint {
 	for {
 		// If there are no more keys then move to the next measurements.
 		if len(itr.buf.keys) == 0 {
@@ -915,7 +937,7 @@ func (itr *TagKeysIterator) Next() *influxql.FloatPoint {
 			}
 
 			itr.buf.mm = itr.mms[0]
-			itr.buf.keys = itr.buf.mm.TagKeys()
+			itr.buf.keys = itr.fn(itr.buf.mm)
 			itr.mms = itr.mms[1:]
 			continue
 		}