Repository: genjidb/genji (go)

Issue:
Add .schema command 
<!-- Answering these questions may help with writing the initial proposal body. Thanks! -->

### Proposal

This is a proposal of `.schema` command to show the `CREATE` statements matching pattern.
The command shows all tables as default or shows the table name option.

Expected: 
```sql
genji> .schema  [table_name]
CREATE TABLE foo (
    bar text NOT NULL,
   baz text NOT NULL
);

CREATE INDEX idx_foo_bar ON foo (bar);

CREATE TABLE bar (
    baz text NOT NULL,
);


```

### Motivation


Like the `.schema`  command of sqlite this is a good command to see the schema of all tables.



Pull request description:
Add .schema command.
Fixes #339.

Patch:
diff --git a/cmd/genji/dbutil/dump.go b/cmd/genji/dbutil/dump.go
index f08eab1c..0ba86028 100644
--- a/cmd/genji/dbutil/dump.go
+++ b/cmd/genji/dbutil/dump.go
@@ -1,12 +1,11 @@
 package dbutil
 
 import (
-	"bytes"
 	"context"
 	"fmt"
 	"io"
 	"strings"
-
+	
 	"github.com/genjidb/genji"
 	"github.com/genjidb/genji/document"
 	"go.uber.org/multierr"
@@ -20,23 +19,23 @@ func Dump(ctx context.Context, db *genji.DB, w io.Writer, tables ...string) erro
 		return err
 	}
 	defer tx.Rollback()
-
+	
 	if _, err = fmt.Fprintln(w, "BEGIN TRANSACTION;"); err != nil {
 		return err
 	}
-
+	
 	query := "SELECT table_name FROM __genji_tables"
 	if len(tables) > 0 {
 		query += " WHERE table_name IN ?"
 	}
-
+	
 	res, err := tx.Query(query, tables)
 	if err != nil {
 		_, er := fmt.Fprintln(w, "ROLLBACK;")
 		return multierr.Append(err, er)
 	}
 	defer res.Close()
-
+	
 	i := 0
 	err = res.Iterate(func(d document.Document) error {
 		// Blank separation between tables.
@@ -46,114 +45,177 @@ func Dump(ctx context.Context, db *genji.DB, w io.Writer, tables ...string) erro
 			}
 		}
 		i++
-
+		
 		// Get table name.
 		var tableName string
 		if err := document.Scan(d, &tableName); err != nil {
 			return err
 		}
-
-		return dumpTable(tx, tableName, w)
+		
+		return dumpTable(tx, w, tableName)
 	})
 	if err != nil {
 		_, er := fmt.Fprintln(w, "ROLLBACK;")
 		return multierr.Append(err, er)
 	}
-
+	
 	_, err = fmt.Fprintln(w, "COMMIT;")
 	return err
 }
 
 // dumpTable displays the content of the given table as SQL statements.
-func dumpTable(tx *genji.Tx, tableName string, w io.Writer) error {
-	var buf bytes.Buffer
-
-	t, err := tx.GetTable(tableName)
+func dumpTable(tx *genji.Tx, w io.Writer, tableName string) error {
+	// Dump schema first.
+	if err := dumpSchema(tx, w, tableName); err != nil {
+		return err
+	}
+	
+	q := fmt.Sprintf("SELECT * FROM %s", tableName)
+	res, err := tx.Query(q)
 	if err != nil {
 		return err
 	}
+	defer res.Close()
+	
+	// Inserts statements.
+	insert := fmt.Sprintf("INSERT INTO %s VALUES", tableName)
+	return res.Iterate(func(d document.Document) error {
+		data, err := document.MarshalJSON(d)
+		if err != nil {
+			return err
+		}
+		
+		if _, err := fmt.Fprintf(w, "%s %s;\n", insert, string(data)); err != nil {
+			return err
+		}
+		
+		return nil
+	})
+}
 
-	if _, err = fmt.Fprintf(w, "CREATE TABLE %s", t.Name()); err != nil {
+// DumpSchema takes a database and dumps its schema as SQL queries in the given writer.
+// If tables are provided, only selected tables will be outputted.
+func DumpSchema(ctx context.Context, db *genji.DB, w io.Writer, tables ...string) error {
+	tx, err := db.Begin(false)
+	if err != nil {
 		return err
 	}
+	defer tx.Rollback()
+	
+	query := "SELECT table_name FROM __genji_tables"
+	if len(tables) > 0 {
+		query += " WHERE table_name IN ?"
+	}
+	
+	res, err := tx.Query(query, tables)
+	if err != nil {
+		return err
+	}
+	defer res.Close()
+	
+	i := 0
+	return res.Iterate(func(d document.Document) error {
+		// Blank separation between tables.
+		if i > 0 {
+			if _, err := fmt.Fprintln(w, ""); err != nil {
+				return err
+			}
+		}
+		i++
+		
+		// Get table name.
+		var tableName string
+		if err := document.Scan(d, &tableName); err != nil {
+			return err
+		}
+		
+		return dumpSchema(tx, w, tableName)
+	})
+}
 
+// dumpSchema displays the schema of the given table as SQL statements.
+func dumpSchema(tx *genji.Tx, w io.Writer, tableName string) error {
+	t, err := tx.GetTable(tableName)
+	if err != nil {
+		return err
+	}
+	
+	_, err = fmt.Fprintf(w, "CREATE TABLE %s", tableName)
+	if err != nil {
+		return err
+	}
+	
 	ti := t.Info()
-
+	
 	fcs := ti.FieldConstraints
 	// Fields constraints should be displayed between parenthesis.
 	if len(fcs) > 0 {
-		buf.WriteString(" (\n")
+		_, err = fmt.Fprintln(w, " (")
+		if err != nil {
+			return err
+		}
 	}
-
+	
 	for i, fc := range fcs {
 		// Don't display the last comma.
 		if i > 0 {
-			buf.WriteString(",\n")
+			_, err = fmt.Fprintln(w, ",")
+			if err != nil {
+				return err
+			}
 		}
-
-		buf.WriteString(" " + fcs[i].Path.String() + " ")
-		buf.WriteString(strings.ToUpper(fcs[i].Type.String()))
+		
+		// Construct the fields constraints
+		if _, err := fmt.Fprintf(w, " %s %s", fcs[i].Path.String(), strings.ToUpper(fcs[i].Type.String())); err != nil {
+			return err
+		}
+		
+		f := ""
 		if fc.IsPrimaryKey {
-			buf.WriteString(" PRIMARY KEY")
+			f += " PRIMARY KEY"
 		}
-
+		
 		if fc.IsNotNull {
-			buf.WriteString(" NOT NULL")
+			f += " NOT NULL"
 		}
-
+		
 		if fc.HasDefaultValue() {
-			buf.WriteString(" DEFAULT ")
-			buf.WriteString(fc.DefaultValue.String())
+			if _, err := fmt.Fprintf(w, "%s DEFAULT %s", f, fc.DefaultValue.String()); err != nil {
+				return err
+			}
+		} else {
+			if _, err := fmt.Fprintf(w, f); err != nil {
+				return err
+			}
 		}
 	}
-
+	
 	// Fields constraints close parenthesis.
 	if len(fcs) > 0 {
-		buf.WriteString("\n);\n")
+		if _, err := fmt.Fprintln(w, "\n);"); err != nil {
+			return err
+		}
 	} else {
-		buf.WriteString(";\n")
-	}
-
-	// Print CREATE TABLE statement.
-	if _, err = buf.WriteTo(w); err != nil {
-		return err
+		if _, err := fmt.Fprintln(w, ";"); err != nil {
+			return err
+		}
 	}
-
+	
 	// Indexes statements.
 	indexes := t.Indexes()
-
+	
 	for _, index := range indexes {
 		u := ""
 		if index.Info.Unique {
 			u = " UNIQUE"
 		}
-
+		
 		_, err = fmt.Fprintf(w, "CREATE%s INDEX %s ON %s (%s);\n", u, index.Info.IndexName, index.Info.TableName,
 			index.Info.Path)
 		if err != nil {
 			return err
 		}
 	}
-
-	q := fmt.Sprintf("SELECT * FROM %s", t.Name())
-	res, err := tx.Query(q)
-	if err != nil {
-		return err
-	}
-	defer res.Close()
-
-	// Inserts statements.
-	insert := fmt.Sprintf("INSERT INTO %s VALUES ", t.Name())
-	return res.Iterate(func(d document.Document) error {
-		buf.WriteString(insert)
-
-		data, err := document.MarshalJSON(d)
-		if err != nil {
-			return err
-		}
-		buf.Write(data)
-		buf.WriteString(";\n")
-		_, err = buf.WriteTo(w)
-		return err
-	})
+	
+	return nil
 }
diff --git a/cmd/genji/shell/command.go b/cmd/genji/shell/command.go
index 8d1e7437..7e011377 100644
--- a/cmd/genji/shell/command.go
+++ b/cmd/genji/shell/command.go
@@ -55,6 +55,12 @@ var commands = []struct {
 		DisplayName: ".save",
 		Description: "Save database content in the specified file.",
 	},
+	{
+		Name:        ".schema",
+		Options:     "[table_name]",
+		DisplayName: ".schema",
+		Description: "Show the CREATE statements matching pattern of a database or the given tables.",
+	},
 }
 
 // runHelpCmd shows all available commands.
diff --git a/cmd/genji/shell/shell.go b/cmd/genji/shell/shell.go
index 46fe1dc1..491e8f57 100644
--- a/cmd/genji/shell/shell.go
+++ b/cmd/genji/shell/shell.go
@@ -482,7 +482,8 @@ func (sh *Shell) runCommand(ctx context.Context, in string) error {
 		}
 
 		return runSaveCmd(ctx, sh.db, engine, path)
-
+	case ".schema":
+		return dbutil.DumpSchema(ctx, sh.db, os.Stdout, cmd[1:]...)
 	default:
 		return displaySuggestions(in)
 	}
diff --git a/document/document.go b/document/document.go
index 491f8cde..76d096e5 100644
--- a/document/document.go
+++ b/document/document.go
@@ -106,6 +106,11 @@ func (fb *FieldBuffer) UnmarshalJSON(data []byte) error {
 	})
 }
 
+func (fb *FieldBuffer) String() string {
+	s, _ := fb.MarshalJSON()
+	return string(s)
+}
+
 type fieldValue struct {
 	Field string
 	Value Value
diff --git a/sql/parser/insert.go b/sql/parser/insert.go
index 9f3b27cb..e6bb182b 100644
--- a/sql/parser/insert.go
+++ b/sql/parser/insert.go
@@ -1,6 +1,8 @@
 package parser
 
 import (
+	"errors"
+
 	"github.com/genjidb/genji/expr"
 	"github.com/genjidb/genji/planner"
 	"github.com/genjidb/genji/sql/scanner"
@@ -28,18 +30,30 @@ func (p *Parser) parseInsertStatement() (*planner.Statement, error) {
 	}
 
 	// Parse path list: (a, b, c)
-	fields, err := p.parseFieldList()
+	cfg.Fields, err = p.parseFieldList()
 	if err != nil {
 		return nil, err
 	}
 
-	// Parse VALUES (v1, v2, v3)
-	cfg.Values, err = p.parseValues(fields)
-	if err != nil {
-		return nil, err
+	// Check if VALUES or SELECT token exists.
+	tok, pos, lit := p.ScanIgnoreWhitespace()
+	switch tok {
+	case scanner.VALUES:
+		// Parse VALUES (v1, v2, v3)
+		cfg.Values, err = p.parseValues(cfg.Fields)
+		if err != nil {
+			return nil, err
+		}
+	case scanner.SELECT:
+		cfg.SelectStmt, err = p.parseSelectStatement()
+		if err != nil {
+			return nil, err
+		}
+	default:
+		return nil, newParseError(scanner.Tokstr(tok, lit), []string{"VALUES", "SELECT"}, pos)
 	}
 
-	return cfg.ToStream(), nil
+	return cfg.ToStream()
 }
 
 // parseFieldList parses a list of fields in the form: (path, path, ...), if exists.
@@ -68,11 +82,6 @@ func (p *Parser) parseFieldList() ([]string, error) {
 
 // parseValues parses the "VALUES" clause of the query, if it exists.
 func (p *Parser) parseValues(fields []string) ([]expr.Expr, error) {
-	// Check if the VALUES token exists.
-	if tok, pos, lit := p.ScanIgnoreWhitespace(); tok != scanner.VALUES {
-		return nil, newParseError(scanner.Tokstr(tok, lit), []string{"VALUES"}, pos)
-	}
-
 	if len(fields) > 0 {
 		return p.parseDocumentsWithFields(fields)
 	}
@@ -182,17 +191,35 @@ func (p *Parser) parseParamOrDocument() (expr.Expr, error) {
 
 // insertConfig holds INSERT configuration.
 type insertConfig struct {
-	TableName string
-	Values    []expr.Expr
+	TableName  string
+	Values     []expr.Expr
+	Fields     []string
+	SelectStmt *planner.Statement
 }
 
-func (cfg *insertConfig) ToStream() *planner.Statement {
-	s := stream.New(stream.Expressions(cfg.Values...))
+func (cfg *insertConfig) ToStream() (*planner.Statement, error) {
+	var s *stream.Stream
+	if cfg.Values != nil {
+		s = stream.New(stream.Expressions(cfg.Values...))
 
-	s = s.Pipe(stream.TableInsert(cfg.TableName))
+		s = s.Pipe(stream.TableInsert(cfg.TableName))
+	} else {
+		s = cfg.SelectStmt.Stream
+
+		// ensure we are not reading and writing to the same table.
+		if s.First().(*stream.SeqScanOperator).TableName == cfg.TableName {
+			return nil, errors.New("cannot read and write to the same table")
+		}
+
+		if len(cfg.Fields) > 0 {
+			s = s.Pipe(stream.IterRename(cfg.Fields...))
+		}
+
+		s = s.Pipe(stream.TableInsert(cfg.TableName))
+	}
 
 	return &planner.Statement{
 		Stream:   s,
 		ReadOnly: false,
-	}
+	}, nil
 }
diff --git a/sql/parser/select.go b/sql/parser/select.go
index 74d02f3c..ac78c5a7 100644
--- a/sql/parser/select.go
+++ b/sql/parser/select.go
@@ -5,7 +5,6 @@ import (
 
 	"github.com/genjidb/genji/expr"
 	"github.com/genjidb/genji/planner"
-	"github.com/genjidb/genji/query"
 	"github.com/genjidb/genji/sql/scanner"
 	"github.com/genjidb/genji/stream"
 	"github.com/genjidb/genji/stringutil"
@@ -13,7 +12,7 @@ import (
 
 // parseSelectStatement parses a select string and returns a Statement AST object.
 // This function assumes the SELECT token has already been consumed.
-func (p *Parser) parseSelectStatement() (query.Statement, error) {
+func (p *Parser) parseSelectStatement() (*planner.Statement, error) {
 	var cfg selectConfig
 	var err error
 
diff --git a/stream/operator.go b/stream/operator.go
index 0fea4d50..0e3dcab7 100644
--- a/stream/operator.go
+++ b/stream/operator.go
@@ -5,6 +5,7 @@ import (
 	"container/heap"
 	"container/list"
 	"errors"
+	"strings"
 
 	"github.com/genjidb/genji/database"
 	"github.com/genjidb/genji/document"
@@ -698,3 +699,70 @@ func (op *UnsetOperator) Iterate(in *expr.Environment, f func(out *expr.Environm
 func (op *UnsetOperator) String() string {
 	return stringutil.Sprintf("unset(%s)", op.Field)
 }
+
+// An IterRenameOperator iterates over all fields of the incoming document in order and renames them.
+type IterRenameOperator struct {
+	baseOperator
+	FieldNames []string
+}
+
+// IterRename iterates over all fields of the incoming document in order and renames them.
+// If the number of fields of the incoming document doesn't match the number of expected fields,
+// it returns an error.
+func IterRename(fieldNames ...string) *IterRenameOperator {
+	return &IterRenameOperator{
+		FieldNames: fieldNames,
+	}
+}
+
+// Iterate implements the Operator interface.
+func (op *IterRenameOperator) Iterate(in *expr.Environment, f func(out *expr.Environment) error) error {
+	var fb document.FieldBuffer
+	var newEnv expr.Environment
+
+	return op.Prev.Iterate(in, func(out *expr.Environment) error {
+		fb.Reset()
+
+		d, ok := out.GetDocument()
+		if !ok {
+			return errors.New("missing document")
+		}
+
+		var i int
+		err := d.Iterate(func(field string, value document.Value) error {
+			// if there are too many fields in the incoming document
+			if i >= len(op.FieldNames) {
+				n, err := document.Length(d)
+				if err != nil {
+					return err
+				}
+				return stringutil.Errorf("%d values for %d fields", n, len(op.FieldNames))
+			}
+
+			fb.Add(op.FieldNames[i], value)
+			i++
+			return nil
+		})
+		if err != nil {
+			return err
+		}
+
+		// if there are too few fields in the incoming document
+		if i < len(op.FieldNames) {
+			n, err := document.Length(d)
+			if err != nil {
+				return err
+			}
+			return stringutil.Errorf("%d values for %d fields", n, len(op.FieldNames))
+		}
+
+		newEnv.Outer = out
+		newEnv.SetDocument(&fb)
+
+		return f(&newEnv)
+	})
+}
+
+func (op *IterRenameOperator) String() string {
+	return stringutil.Sprintf("iterRename(%s)", strings.Join(op.FieldNames, ", "))
+}


Test patch:
diff --git a/cmd/genji/dbutil/dump_test.go b/cmd/genji/dbutil/dump_test.go
index 4fd8d3b2..cb306dd9 100644
--- a/cmd/genji/dbutil/dump_test.go
+++ b/cmd/genji/dbutil/dump_test.go
@@ -88,3 +88,65 @@ func TestDump(t *testing.T) {
 		})
 	}
 }
+
+func TestDumpSchema(t *testing.T) {
+	tests := []struct {
+		name   string
+		tables []string
+	}{
+		{"All tables", nil},
+		{"Selection of tables", []string{"test", "foo"}},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			db, err := genji.Open(":memory:")
+			require.NoError(t, err)
+			defer db.Close()
+
+			var want bytes.Buffer
+
+			getBuffer := func(table string) func(s string) {
+				writeFn := func(s string) {
+					want.WriteString(s)
+				}
+				noOp := func(s string) {}
+
+				if len(tt.tables) == 0 {
+					return writeFn
+				}
+
+				for _, tb := range tt.tables {
+					if tb == table {
+						return writeFn
+					}
+				}
+				return noOp
+			}
+
+			for i, table := range []string{"tblA", "tblB"} {
+				writeToBuf := getBuffer(table)
+
+				if i > 0 {
+					writeToBuf("\n")
+				}
+
+				q := fmt.Sprintf("CREATE TABLE %s (\n a INTEGER\n);", table)
+				err = db.Exec(q)
+				require.NoError(t, err)
+				writeToBuf(q + "\n")
+
+				q = fmt.Sprintf(`CREATE INDEX idx_a_%s ON %s (a);`, table, table)
+				err = db.Exec(q)
+				require.NoError(t, err)
+				writeToBuf(q + "\n")
+			}
+
+			var got bytes.Buffer
+			err = DumpSchema(context.Background(), db, &got, tt.tables...)
+			require.NoError(t, err)
+
+			require.Equal(t, want.String(), got.String())
+		})
+	}
+}
diff --git a/query/insert_test.go b/query/insert_test.go
index 08c3036b..036b036d 100644
--- a/query/insert_test.go
+++ b/query/insert_test.go
@@ -276,3 +276,54 @@ func TestInsertStmt(t *testing.T) {
 		}
 	})
 }
+
+func TestInsertSelect(t *testing.T) {
+	tests := []struct {
+		name     string
+		query    string
+		fails    bool
+		expected string
+		params   []interface{}
+	}{
+		{"Same table", `INSERT INTO foo SELECT * FROM foo`, true, ``, nil},
+		{"No fields / No projection", `INSERT INTO foo SELECT * FROM bar`, false, `[{"pk()":1, "a":1, "b":10}]`, nil},
+		{"No fields / Projection", `INSERT INTO foo SELECT a FROM bar`, false, `[{"pk()":1, "a":1}]`, nil},
+		{"With fields / No Projection", `INSERT INTO foo (a, b) SELECT * FROM bar`, false, `[{"pk()":1, "a":1, "b":10}]`, nil},
+		{"With fields / Projection", `INSERT INTO foo (c, d) SELECT a, b FROM bar`, false, `[{"pk()":1, "c":1, "d":10}]`, nil},
+		{"Too many fields / No Projection", `INSERT INTO foo (c) SELECT * FROM bar`, true, ``, nil},
+		{"Too many fields / Projection", `INSERT INTO foo (c, d) SELECT a, b, c FROM bar`, true, ``, nil},
+		{"Too few fields / No Projection", `INSERT INTO foo (c, d, e) SELECT * FROM bar`, true, ``, nil},
+		{"Too few fields / Projection", `INSERT INTO foo (c, d) SELECT a FROM bar`, true, ``, nil},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			db, err := genji.Open(":memory:")
+			require.NoError(t, err)
+			defer db.Close()
+
+			err = db.Exec(`
+				CREATE TABLE foo;
+				CREATE TABLE bar;
+				INSERT INTO bar (a, b) VALUES (1, 10)
+			`)
+			require.NoError(t, err)
+
+			err = db.Exec(test.query, test.params...)
+			if test.fails {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+
+			st, err := db.Query("SELECT pk(), * FROM foo")
+			require.NoError(t, err)
+			defer st.Close()
+
+			var buf bytes.Buffer
+			err = document.IteratorToJSONArray(&buf, st)
+			require.NoError(t, err)
+			require.JSONEq(t, test.expected, buf.String())
+		})
+	}
+}
diff --git a/sql/parser/insert_test.go b/sql/parser/insert_test.go
index 6e720c72..27a480b5 100644
--- a/sql/parser/insert_test.go
+++ b/sql/parser/insert_test.go
@@ -76,6 +76,36 @@ func TestParserInsert(t *testing.T) {
 			nil, true},
 		{"Values / Without fields / Wrong values", "INSERT INTO test VALUES {a: 1}, ('e', 'f')",
 			nil, true},
+		{"Select / same table", "INSERT INTO test SELECT * FROM test",
+			nil, true},
+		{"Select / Without fields", "INSERT INTO test SELECT * FROM foo",
+			stream.New(stream.SeqScan("foo")).
+				Pipe(stream.Project(expr.Wildcard{})).
+				Pipe(stream.TableInsert("test")),
+			false},
+		{"Select / Without fields / With projection", "INSERT INTO test SELECT a, b FROM foo",
+			stream.New(stream.SeqScan("foo")).
+				Pipe(stream.Project(parseNamedExpr(t, "a"), parseNamedExpr(t, "b"))).
+				Pipe(stream.TableInsert("test")),
+			false},
+		{"Select / With fields", "INSERT INTO test (a, b) SELECT * FROM foo",
+			stream.New(stream.SeqScan("foo")).
+				Pipe(stream.Project(expr.Wildcard{})).
+				Pipe(stream.IterRename("a", "b")).
+				Pipe(stream.TableInsert("test")),
+			false},
+		{"Select / With fields / With projection", "INSERT INTO test (a, b) SELECT a, b FROM foo",
+			stream.New(stream.SeqScan("foo")).
+				Pipe(stream.Project(parseNamedExpr(t, "a"), parseNamedExpr(t, "b"))).
+				Pipe(stream.IterRename("a", "b")).
+				Pipe(stream.TableInsert("test")),
+			false},
+		{"Select / With fields / With projection / different fields", "INSERT INTO test (a, b) SELECT c, d FROM foo",
+			stream.New(stream.SeqScan("foo")).
+				Pipe(stream.Project(parseNamedExpr(t, "c"), parseNamedExpr(t, "d"))).
+				Pipe(stream.IterRename("a", "b")).
+				Pipe(stream.TableInsert("test")),
+			false},
 	}
 
 	for _, test := range tests {
@@ -89,7 +119,7 @@ func TestParserInsert(t *testing.T) {
 			require.Len(t, q.Statements, 1)
 			stmt := q.Statements[0].(*planner.Statement)
 			require.False(t, stmt.ReadOnly)
-			require.EqualValues(t, test.expected, stmt.Stream)
+			require.EqualValues(t, test.expected.String(), stmt.Stream.String())
 		})
 	}
 }
diff --git a/stream/operator_test.go b/stream/operator_test.go
index 5726ac0b..3c6aacdd 100644
--- a/stream/operator_test.go
+++ b/stream/operator_test.go
@@ -709,3 +709,52 @@ func TestUnset(t *testing.T) {
 		require.Equal(t, stream.Unset("a").String(), "unset(a)")
 	})
 }
+
+func TestIterRename(t *testing.T) {
+	tests := []struct {
+		fieldNames []string
+		in, out    []document.Document
+		fails      bool
+	}{
+		{
+			[]string{"c", "d"},
+			testutil.MakeDocuments(t, `{"a": 10, "b": 20}`),
+			testutil.MakeDocuments(t, `{"c": 10, "d": 20}`),
+			false,
+		},
+		{
+			[]string{"c", "d", "e"},
+			testutil.MakeDocuments(t, `{"a": 10, "b": 20}`),
+			nil,
+			true,
+		},
+		{
+			[]string{"c"},
+			testutil.MakeDocuments(t, `{"a": 10, "b": 20}`),
+			nil,
+			true,
+		},
+	}
+
+	for _, test := range tests {
+		s := stream.New(stream.Documents(test.in...)).Pipe(stream.IterRename(test.fieldNames...))
+		t.Run(s.String(), func(t *testing.T) {
+			i := 0
+			err := s.Iterate(nil, func(out *expr.Environment) error {
+				d, _ := out.GetDocument()
+				require.Equal(t, test.out[i], d)
+				i++
+				return nil
+			})
+			if test.fails {
+				require.Error(t, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+
+	t.Run("String", func(t *testing.T) {
+		require.Equal(t, stream.IterRename("a", "b", "c").String(), "iterRename(a, b, c)")
+	})
+}