sql: support DESCRIBE table.

README.md

@@ -58,6 +58,7 @@ gitql supports a subset of the SQL standard, currently including:
 * `ORDER BY` (with `ASC` and `DESC`)
 * `LIMIT`
 * `SHOW TABLES`
+* `DESCRIBE TABLE`
 
 ## License
 

sql/analyzer/analyzer_test.go

@@ -45,13 +45,21 @@ func TestAnalyzer_Analyze(t *testing.T) {
 		plan.NewUnresolvedTable("mytable"),
 	)
 	analyzed, err = a.Analyze(notAnalyzed)
-	expected := plan.NewProject(
+	var expected sql.Node = plan.NewProject(
 		[]sql.Expression{expression.NewGetField(0, sql.Integer, "i")},
 		table,
 	)
 	assert.Nil(err)
 	assert.Equal(expected, analyzed)
 
+	notAnalyzed = plan.NewDescribe(
+		plan.NewUnresolvedTable("mytable"),
+	)
+	analyzed, err = a.Analyze(notAnalyzed)
+	expected = plan.NewDescribe(table)
+	assert.Nil(err)
+	assert.Equal(expected, analyzed)
+
 	notAnalyzed = plan.NewProject(
 		[]sql.Expression{expression.NewStar()},
 		plan.NewUnresolvedTable("mytable"),

sql/parse/parse.go

@@ -2,6 +2,7 @@ package parse
 
 import (
 	"fmt"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -34,6 +35,11 @@ func Parse(s string) (sql.Node, error) {
 		return plan.NewShowTables(&sql.UnresolvedDatabase{}), nil
 	}
 
+	t := regexp.MustCompile(`^describe\s+table\s+(.*)`).FindStringSubmatch(strings.ToLower(s))
+	if len(t) == 2 && t[1] != "" {
+		return plan.NewDescribe(plan.NewUnresolvedTable(t[1])), nil
+	}
+
 	stmt, err := sqlparser.Parse(s)
 	if err != nil {
 		return nil, err

sql/parse/parse_test.go

@@ -11,6 +11,9 @@ import (
 )
 
 var fixtures = map[string]sql.Node{
+	`DESCRIBE TABLE foo;`: plan.NewDescribe(
+		plan.NewUnresolvedTable("foo"),
+	),
 	`SELECT foo, bar FROM foo;`: plan.NewProject(
 		[]sql.Expression{
 			expression.NewUnresolvedColumn("foo"),

sql/plan/common.go

@@ -6,6 +6,10 @@ type UnaryNode struct {
 	Child sql.Node
 }
 
+func (n UnaryNode) Resolved() bool {
+	return n.Child.Resolved()
+}
+
 func (n UnaryNode) Children() []sql.Node {
 	return []sql.Node{n.Child}
 }

sql/plan/describe.go

@@ -0,0 +1,61 @@
+package plan
+
+import (
+	"io"
+
+	"github.com/gitql/gitql/sql"
+)
+
+type Describe struct {
+	UnaryNode
+}
+
+func NewDescribe(child sql.Node) *Describe {
+	return &Describe{UnaryNode{child}}
+}
+
+func (d *Describe) Schema() sql.Schema {
+	return sql.Schema{
+		sql.Field{
+			Name: "name",
+			Type: sql.String,
+		},
+		sql.Field{
+			Name: "type",
+			Type: sql.String,
+		},
+	}
+}
+
+func (d *Describe) RowIter() (sql.RowIter, error) {
+	return &describeIter{schema: d.Child.Schema()}, nil
+}
+
+func (d *Describe) TransformUp(f func(sql.Node) sql.Node) sql.Node {
+	c := d.UnaryNode.Child.TransformUp(f)
+	n := NewDescribe(c)
+
+	return f(n)
+}
+
+func (d *Describe) TransformExpressionsUp(f func(sql.Expression) sql.Expression) sql.Node {
+	c := d.UnaryNode.Child.TransformExpressionsUp(f)
+	n := NewDescribe(c)
+
+	return n
+}
+
+type describeIter struct {
+	schema sql.Schema
+	i      int
+}
+
+func (i *describeIter) Next() (sql.Row, error) {
+	if i.i >= len(i.schema) {
+		return nil, io.EOF
+	}
+
+	f := i.schema[i.i]
+	i.i++
+	return sql.NewMemoryRow(f.Name, f.Type.Name()), nil
+}

sql/plan/describe_test.go

@@ -0,0 +1,50 @@
+package plan
+
+import (
+	"io"
+	"testing"
+
+	"github.com/gitql/gitql/mem"
+	"github.com/gitql/gitql/sql"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDescribe(t *testing.T) {
+	assert := assert.New(t)
+
+	table := mem.NewTable("test", sql.Schema{
+		sql.Field{Name: "c1", Type: sql.String},
+		sql.Field{Name: "c2", Type: sql.Integer},
+	})
+
+	d := NewDescribe(table)
+	iter, err := d.RowIter()
+	assert.Nil(err)
+	assert.NotNil(iter)
+
+	n, err := iter.Next()
+	assert.Nil(err)
+	assert.Equal(sql.NewMemoryRow("c1", "string"), n)
+
+	n, err = iter.Next()
+	assert.Nil(err)
+	assert.Equal(sql.NewMemoryRow("c2", "integer"), n)
+
+	n, err = iter.Next()
+	assert.Equal(io.EOF, err)
+	assert.Nil(n)
+}
+
+func TestDescribe_Empty(t *testing.T) {
+	assert := assert.New(t)
+
+	d := NewDescribe(NewUnresolvedTable("test_table"))
+
+	iter, err := d.RowIter()
+	assert.Nil(err)
+	assert.NotNil(iter)
+
+	n, err := iter.Next()
+	assert.Equal(io.EOF, err)
+	assert.Nil(n)
+}