From 945af954fc28cc4f274d0561b0a59c8da9d14e1d Mon Sep 17 00:00:00 2001
From: Harshit Gangal <harshit@planetscale.com>
Date: Mon, 13 Jan 2025 14:41:05 +0530
Subject: [PATCH] describe statement: support global routing

Signed-off-by: Harshit Gangal <harshit@planetscale.com>
---
 go/vt/vtgate/planbuilder/plan_test.go         |  4 +-
 .../testdata/other_read_cases.json            | 60 +++++++++++++------
 go/vt/vtgate/planbuilder/vexplain.go          | 24 ++++----
 3 files changed, 55 insertions(+), 33 deletions(-)

diff --git a/go/vt/vtgate/planbuilder/plan_test.go b/go/vt/vtgate/planbuilder/plan_test.go
index f3bed93e3c8..8a8d55279a6 100644
--- a/go/vt/vtgate/planbuilder/plan_test.go
+++ b/go/vt/vtgate/planbuilder/plan_test.go
@@ -577,10 +577,10 @@ func (s *planTestSuite) TestOtherPlanningFromFile() {
 	vw, err := vschemawrapper.NewVschemaWrapper(env, vschema, TestBuilder)
 	require.NoError(s.T(), err)
 
+	s.testFile("other_read_cases.json", vw, false)
+
 	vw.Vcursor.SetTarget("main")
 	vw.Keyspace = &vindexes.Keyspace{Name: "main"}
-
-	s.testFile("other_read_cases.json", vw, false)
 	s.testFile("other_admin_cases.json", vw, false)
 }
 
diff --git a/go/vt/vtgate/planbuilder/testdata/other_read_cases.json b/go/vt/vtgate/planbuilder/testdata/other_read_cases.json
index 2258bcd768c..1a7c9ddac2a 100644
--- a/go/vt/vtgate/planbuilder/testdata/other_read_cases.json
+++ b/go/vt/vtgate/planbuilder/testdata/other_read_cases.json
@@ -8,24 +8,24 @@
       "Instructions": {
         "OperatorType": "Send",
         "Keyspace": {
-          "Name": "main",
-          "Sharded": false
+          "Name": "user",
+          "Sharded": true
         },
         "TargetDestination": "AnyShard()",
         "Query": "explain select * from `user`",
         "SingleShardOnly": true
       },
       "TablesUsed": [
-        "main.user"
+        "user.user"
       ]
     }
   },
   {
     "comment": "Analyze statement",
-    "query": "analyze table t1",
+    "query": "analyze table main.t1",
     "plan": {
       "QueryType": "ANALYZE",
-      "Original": "analyze table t1",
+      "Original": "analyze table main.t1",
       "Instructions": {
         "OperatorType": "Send",
         "Keyspace": {
@@ -42,43 +42,43 @@
   },
   {
     "comment": "Describe statement",
-    "query": "describe select * from t",
+    "query": "describe select * from user",
     "plan": {
       "QueryType": "EXPLAIN",
-      "Original": "describe select * from t",
+      "Original": "describe select * from user",
       "Instructions": {
         "OperatorType": "Send",
         "Keyspace": {
-          "Name": "main",
-          "Sharded": false
+          "Name": "user",
+          "Sharded": true
         },
         "TargetDestination": "AnyShard()",
-        "Query": "explain select * from t",
+        "Query": "explain select * from `user`",
         "SingleShardOnly": true
       },
       "TablesUsed": [
-        "main.t"
+        "user.user"
       ]
     }
   },
   {
     "comment": "Desc statement",
-    "query": "desc select * from t",
+    "query": "desc select * from user",
     "plan": {
       "QueryType": "EXPLAIN",
-      "Original": "desc select * from t",
+      "Original": "desc select * from user",
       "Instructions": {
         "OperatorType": "Send",
         "Keyspace": {
-          "Name": "main",
-          "Sharded": false
+          "Name": "user",
+          "Sharded": true
         },
         "TargetDestination": "AnyShard()",
-        "Query": "explain select * from t",
+        "Query": "explain select * from `user`",
         "SingleShardOnly": true
       },
       "TablesUsed": [
-        "main.t"
+        "user.user"
       ]
     }
   },
@@ -167,5 +167,31 @@
         "main.administrable_role_authorizations"
       ]
     }
+  },
+  {
+    "comment": "describe table without qualifier",
+    "query": "describe user",
+    "plan": {
+      "QueryType": "EXPLAIN",
+      "Original": "describe user",
+      "Instructions": {
+        "OperatorType": "Send",
+        "Keyspace": {
+          "Name": "user",
+          "Sharded": true
+        },
+        "TargetDestination": "AnyShard()",
+        "Query": "explain `user`",
+        "SingleShardOnly": true
+      },
+      "TablesUsed": [
+        "user.user"
+      ]
+    }
+  },
+  {
+    "comment": "describe table does not exists",
+    "query": "describe unknown_table",
+    "plan": "table unknown_table not found"
   }
 ]
diff --git a/go/vt/vtgate/planbuilder/vexplain.go b/go/vt/vtgate/planbuilder/vexplain.go
index 7aed1e48884..a12139c3068 100644
--- a/go/vt/vtgate/planbuilder/vexplain.go
+++ b/go/vt/vtgate/planbuilder/vexplain.go
@@ -55,7 +55,7 @@ func buildVExplainPlan(
 
 func explainTabPlan(explain *sqlparser.ExplainTab, vschema plancontext.VSchema) (*planResult, error) {
 	var keyspace *vindexes.Keyspace
-	var destination key.Destination
+	var dest key.Destination
 
 	if sqlparser.SystemSchema(explain.Table.Qualifier.String()) {
 		var err error
@@ -64,30 +64,26 @@ func explainTabPlan(explain *sqlparser.ExplainTab, vschema plancontext.VSchema)
 			return nil, err
 		}
 	} else {
+		var tbl *vindexes.Table
 		var err error
-		var ks string
-		_, _, ks, _, destination, err = vschema.FindTableOrVindex(explain.Table)
+		tbl, _, _, _, dest, err = vschema.FindTableOrVindex(explain.Table)
 		if err != nil {
 			return nil, err
 		}
-		explain.Table.Qualifier = sqlparser.NewIdentifierCS("")
-
-		keyspace, err = vschema.FindKeyspace(ks)
-		if err != nil {
-			return nil, err
-		}
-		if keyspace == nil {
-			return nil, vterrors.VT14004(ks)
+		if tbl == nil {
+			return nil, vterrors.VT05004(explain.Table.Name.String())
 		}
+		keyspace = tbl.Keyspace
+		explain.Table = sqlparser.NewTableName(tbl.Name.String())
 	}
 
-	if destination == nil {
-		destination = key.DestinationAnyShard{}
+	if dest == nil {
+		dest = key.DestinationAnyShard{}
 	}
 
 	return newPlanResult(&engine.Send{
 		Keyspace:          keyspace,
-		TargetDestination: destination,
+		TargetDestination: dest,
 		Query:             sqlparser.String(explain),
 		SingleShardOnly:   true,
 	}, singleTable(keyspace.Name, explain.Table.Name.String())), nil