added test and example for explain query

query/example_test.go

@@ -124,6 +124,33 @@ func Example_queryRow() {
 	fmt.Printf("id=%v, myStr='%s'\n", id, myStr)
 }
 
+func Example_explain() {
+	ctx := context.TODO()
+	db, err := ydb.Open(ctx, "grpc://localhost:2136/local")
+	if err != nil {
+		panic(err)
+	}
+	defer db.Close(ctx) // cleanup resources
+	var (
+		ast  string
+		plan string
+	)
+	err = db.Query().Exec(ctx,
+		`SELECT CAST(42 AS Uint32);`,
+		query.WithExecMode(query.ExecModeExplain),
+		query.WithStatsMode(query.StatsModeNone, func(stats query.Stats) {
+			ast = stats.QueryAST()
+			plan = stats.QueryPlan()
+		}),
+		query.WithIdempotent(),
+	)
+	if err != nil {
+		panic(err)
+	}
+	fmt.Println(plan)
+	fmt.Println(ast)
+}
+
 func Example_withoutRangeIterators() {
 	ctx := context.TODO()
 	db, err := ydb.Open(ctx, "grpc://localhost:2136/local")

tests/integration/query_execute_test.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"regexp"
 	"testing"
 	"time"
 
@@ -92,6 +93,40 @@ func TestQueryExecute(t *testing.T) {
 			require.True(t, ok)
 		})
 	})
+	t.Run("Explain", func(t *testing.T) {
+		var (
+			ast  string
+			plan string
+		)
+		err := db.Query().Exec(ctx,
+			`SELECT CAST(42 AS Uint32);`,
+			query.WithExecMode(query.ExecModeExplain),
+			query.WithStatsMode(query.StatsModeNone, func(stats query.Stats) {
+				ast = stats.QueryAST()
+				plan = stats.QueryPlan()
+			}),
+			query.WithIdempotent(),
+		)
+		require.NoError(t, err)
+		require.EqualValues(t,
+			`{"Plan":{"Plans":[{"PlanNodeId":2,"Plans":[{"PlanNodeId":1,"Operators":[{"Inputs":[],"Iterator":"[{column0: 42}]","Name":"Iterator"}],"Node Type":"ConstantExpr"}],"Node Type":"ResultSet","PlanNodeType":"ResultSet"}],"Node Type":"Query","PlanNodeType":"Query"},"meta":{"version":"0.2","type":"query"},"tables":[],"SimplifiedPlan":{"PlanNodeId":0,"Plans":[{"PlanNodeId":1,"Node Type":"ResultSet","PlanNodeType":"ResultSet"}],"Node Type":"Query","PlanNodeType":"Query"}}`,
+			plan,
+		)
+		ast = regexp.MustCompile("\"_id\" '\"(\\w{8}-\\w{8}-\\w{8}-\\w{8})\"").ReplaceAllStringFunc(ast, func(string) string {
+			return `"_id" '"test-id"`
+		})
+		require.EqualValues(t,
+			`(
+(let $1 (OptionalType (DataType 'Uint32)))
+(let $2 '('('"_logical_id" '184) '('"_id" '"test-id") '('"_partition_mode" '"single")))
+(let $3 (DqPhyStage '() (lambda '() (Iterator (AsList (AsStruct '('"column0" (SafeCast (Int32 '"42") $1)))))) $2))
+(let $4 (DqCnResult (TDqOutput $3 '"0") '('"column0")))
+(return (KqpPhysicalQuery '((KqpPhysicalTx '($3) '($4) '() '('('"type" '"generic")))) '((KqpTxResultBinding (ListType (StructType '('"column0" $1))) '"0" '"0")) '('('"type" '"query"))))
+)
+`,
+			ast,
+		)
+	})
 	t.Run("Scan", func(t *testing.T) {
 		var (
 			p1 string