fix inverted index IN filter error (#1146)

* fix inverted index IN filter error

* delete stale error

enginetest/queries/queries.go

@@ -6766,6 +6766,10 @@ var QueryTests = []QueryTest{
 		Query:    `select * from mytable where 1 = 0 order by i asc`,
 		Expected: []sql.Row{},
 	},
+	{
+		Query:    `select * from mytable where i not in (1)`,
+		Expected: []sql.Row{{2, "second row"}, {3, "third row"}},
+	},
 }
 
 var KeylessQueries = []QueryTest{

sql/analyzer/indexes.go

@@ -15,15 +15,11 @@
 package analyzer
 
 import (
-	errors "gopkg.in/src-d/go-errors.v1"
-
 	"github.com/dolthub/go-mysql-server/sql"
 	"github.com/dolthub/go-mysql-server/sql/expression"
 	"github.com/dolthub/go-mysql-server/sql/plan"
 )
 
-var errInvalidInRightEvaluation = errors.NewKind("expecting evaluation of IN expression right hand side to be a tuple, but it is %T")
-
 // indexLookup contains an sql.IndexLookup and all sql.Index that are involved
 // in it.
 type indexLookup struct {
@@ -449,9 +445,12 @@ func getNegatedIndexes(
 					return nil, err
 				}
 
-				values, ok := value.([]interface{})
-				if !ok {
-					return nil, errInvalidInRightEvaluation.New(value)
+				var values []interface{}
+				switch v := value.(type) {
+				case []interface{}:
+					values = v
+				default:
+					values = []interface{}{v}
 				}
 
 				idxBuilder := sql.NewIndexBuilder(ctx, idx)