fix: allow passed table_schema in information_schema queries to vttablet if the keyspace is not found

go/test/endtoend/vtgate/misc_test.go

@@ -288,6 +288,37 @@ func TestShowTablesWithWhereClause(t *testing.T) {
 	assertMatches(t, conn, "show tables from ks where Tables_in_ks='t3'", `[[VARCHAR("t3")]]`)
 }
 
+func TestDbNameOverride(t *testing.T) {
+	defer cluster.PanicHandler(t)
+	ctx := context.Background()
+	conn, err := mysql.Connect(ctx, &vtParams)
+	require.Nil(t, err)
+	defer conn.Close()
+	qr, err := conn.ExecuteFetch("SELECT distinct database() FROM information_schema.tables WHERE table_schema = database()", 1000, true)
+
+	require.Nil(t, err)
+	assert.Equal(t, 1, len(qr.Rows), "did not get enough rows back")
+	assert.Equal(t, "vt_ks", qr.Rows[0][0].ToString())
+}
+
+func TestInformationSchemaQuery(t *testing.T) {
+	defer cluster.PanicHandler(t)
+	ctx := context.Background()
+	conn, err := mysql.Connect(ctx, &vtParams)
+	require.Nil(t, err)
+	defer conn.Close()
+
+	qr, err := conn.ExecuteFetch("SELECT distinct table_schema FROM information_schema.tables WHERE table_schema = 'ks'", 1000, true)
+	require.Nil(t, err)
+	assert.Equal(t, 1, len(qr.Rows), "did not get enough rows back")
+	assert.Equal(t, "vt_ks", qr.Rows[0][0].ToString())
+
+	qr, err = conn.ExecuteFetch("SELECT distinct table_schema FROM information_schema.tables WHERE table_schema = 'vt_ks'", 1000, true)
+	require.Nil(t, err)
+	assert.Equal(t, 1, len(qr.Rows), "did not get enough rows back")
+	assert.Equal(t, "vt_ks", qr.Rows[0][0].ToString())
+}
+
 func assertMatches(t *testing.T, conn *mysql.Conn, query, expected string) {
 	t.Helper()
 	qr := exec(t, conn, query)

go/vt/vtgate/engine/route.go

@@ -186,6 +186,8 @@ var routeName = map[RouteOpcode]string{
 
 var (
 	partialSuccessScatterQueries = stats.NewCounter("PartialSuccessScatterQueries", "Count of partially successful scatter queries")
+	// BvSchemaName is bind variable to be sent down to vttablet for schema name.
+	BvSchemaName = "__vtschemaname"
 )
 
 // MarshalJSON serializes the RouteOpcode as a JSON string.
@@ -391,6 +393,7 @@ func (route *Route) paramsSystemQuery(vcursor VCursor, bindVars map[string]*quer
 		}
 		if keyspace == "" {
 			keyspace = result.Value().ToString()
+			bindVars[BvSchemaName] = sqltypes.StringBindVariable(keyspace)
 		} else if other := result.Value().ToString(); keyspace != other {
 			return nil, nil, vterrors.Errorf(vtrpcpb.Code_INVALID_ARGUMENT, "can't use more than one keyspace per system table query - found both '%s' and '%s'", keyspace, other)
 		}
@@ -402,7 +405,11 @@ func (route *Route) paramsSystemQuery(vcursor VCursor, bindVars map[string]*quer
 
 	destinations, _, err := vcursor.ResolveDestinations(keyspace, nil, []key.Destination{key.DestinationAnyShard{}})
 	if err != nil {
-		return nil, nil, vterrors.Wrapf(err, "failed to find information about keyspace `%s`", keyspace)
+		// Check with assigned route keyspace.
+		destinations, _, err = vcursor.ResolveDestinations(route.Keyspace.Name, nil, []key.Destination{key.DestinationAnyShard{}})
+		if err != nil {
+			return nil, nil, vterrors.Wrapf(err, "failed to find information about keyspace `%s`", keyspace)
+		}
 	}
 	return destinations, []map[string]*querypb.BindVariable{bindVars}, nil
 }

go/vt/vtgate/planbuilder/select.go

@@ -257,7 +257,7 @@ func (r *rewriter) rewriteTableSchema(cursor *sqlparser.Cursor) bool {
 						return false
 					}
 					r.tableNameExpressions = append(r.tableNameExpressions, evalExpr)
-					parent.Right = sqlparser.NewArgument([]byte(":__vtschemaname"))
+					parent.Right = sqlparser.NewArgument([]byte(":" + engine.BvSchemaName))
 				}
 			}
 		}