Handle null index column names in sql.DB loader (#904)

For developers using multi-value indexes, the column name as reported by `show index...` is null.

Author: shauns

schema/schema.go

@@ -354,7 +354,8 @@ func (ta *Table) fetchIndexesViaSqlDB(conn *sql.DB) error {
 	var unusedVal interface{}
 
 	for r.Next() {
-		var indexName, colName string
+		var indexName string
+		var colName sql.NullString
 		var noneUnique uint64
 		var cardinality interface{}
 		cols, err := r.Columns()
@@ -387,7 +388,12 @@ func (ta *Table) fetchIndexesViaSqlDB(conn *sql.DB) error {
 		}
 
 		c := toUint64(cardinality)
-		currentIndex.AddColumn(colName, c)
+		// If colName is a null string, switch to ""
+		if colName.Valid {
+			currentIndex.AddColumn(colName.String, c)
+		} else {
+			currentIndex.AddColumn("", c)
+		}
 		currentIndex.NoneUnique = noneUnique
 	}
 

schema/schema_test.go

@@ -134,3 +134,41 @@ func (s *schemaTestSuite) TestQuoteSchema() {
 
 	require.Equal(s.T(), "a.b", ta.Columns[0].Name)
 }
+
+func (s *schemaTestSuite) TestSchemaWithMultiValueIndex() {
+	_, err := s.conn.Execute(`DROP TABLE IF EXISTS multi_value_idx_test`)
+	require.NoError(s.T(), err)
+
+	str := `
+        CREATE TABLE IF NOT EXISTS multi_value_idx_test (
+            id INT,
+            entries json,
+            PRIMARY KEY(id)
+        ) ENGINE = INNODB;
+    `
+
+	_, err = s.conn.Execute(str)
+	require.NoError(s.T(), err)
+
+	str = `CREATE INDEX idx_entries ON multi_value_idx_test((CAST((entries->'$') AS CHAR(64))));`
+	_, err = s.conn.Execute(str)
+	require.NoError(s.T(), err)
+
+	ta, err := NewTable(s.conn, *schema, "multi_value_idx_test")
+	require.NoError(s.T(), err)
+
+	require.Len(s.T(), ta.Indexes, 2)
+
+	require.Equal(s.T(), "PRIMARY", ta.Indexes[0].Name)
+	require.Len(s.T(), ta.Indexes[0].Columns, 1)
+	require.Equal(s.T(), "id", ta.Indexes[0].Columns[0])
+
+	require.Equal(s.T(), "idx_entries", ta.Indexes[1].Name)
+	require.Len(s.T(), ta.Indexes[1].Columns, 1)
+	require.Equal(s.T(), "", ta.Indexes[1].Columns[0])
+
+	taSqlDb, err := NewTableFromSqlDB(s.sqlDB, *schema, "multi_value_idx_test")
+	require.NoError(s.T(), err)
+
+	require.Equal(s.T(), ta, taSqlDb)
+}