syntax support for custom explain plan

go/vt/sqlparser/ast.go

@@ -3936,6 +3936,7 @@ const (
 // Explain represents an explain statement
 type Explain struct {
 	Statement     Statement
+	Plan          bool
 	Analyze       bool
 	ExplainFormat string
 }
@@ -3950,7 +3951,11 @@ func (node *Explain) Format(buf *TrackedBuffer) {
 	if !node.Analyze && node.ExplainFormat != "" {
 		formatOpt = fmt.Sprintf("format = %s ", node.ExplainFormat)
 	}
-	buf.Myprintf("explain %s%s%v", analyzeOpt, formatOpt, node.Statement)
+	planOpt := ""
+	if node.Plan {
+		planOpt = "plan "
+	}
+	buf.Myprintf("explain %s%s%s%v", analyzeOpt, formatOpt, planOpt, node.Statement)
 }
 
 const (

go/vt/sqlparser/keywords.go

@@ -466,6 +466,7 @@ var keywords = map[string]int{
 	"persist":                       PERSIST,
 	"persist_only":                  PERSIST_ONLY,
 	"persist_ro_variables_admin":    PERSIST_RO_VARIABLES_ADMIN,
+	"plan":                          PLAN,
 	"plugins":                       PLUGINS,
 	"point":                         POINT,
 	"polygon":                       POLYGON,

go/vt/sqlparser/parse_test.go

@@ -2459,22 +2459,54 @@ var (
 		}, {
 			input:  "show columns from a for system_time as of 'foo'",
 			output: "show columns from a as of 'foo'",
-		}, {
+		},
+		{
 			input: "explain select * from foobar",
-		}, {
+		},
+		{
 			input: "explain format = tree select * from foobar",
-		}, {
+		},
+		{
 			input: "explain analyze select * from foobar",
-		}, {
+		},
+		{
 			input:  "explain extended select * from foobar",
 			output: "explain select * from foobar",
-		}, {
+		},
+		{
 			input: "explain update foobar set foo = bar",
-		}, {
+		},
+		{
 			input: "explain delete from foobar where foo = bar",
-		}, {
+		},
+		{
 			input: "explain insert into foobar values (1, 2, 3)",
-		}, {
+		},
+
+		{
+			input: "explain plan select * from foobar",
+		},
+		{
+			input: "explain format = tree plan select * from foobar",
+		},
+		{
+			input: "explain analyze plan select * from foobar",
+		},
+		{
+			input:  "explain extended plan select * from foobar",
+			output: "explain plan select * from foobar",
+		},
+		{
+			input: "explain plan update foobar set foo = bar",
+		},
+		{
+			input: "explain plan delete from foobar where foo = bar",
+		},
+		{
+			input: "explain plan insert into foobar values (1, 2, 3)",
+		},
+
+		{
 			input:  "truncate table foo",
 			output: "truncate table foo",
 		}, {