yii\db\sqlite\Schema::findUniqueIndexes PHP Method

    public function findUniqueIndexes($table)
    {
        $sql = 'PRAGMA index_list(' . $this->quoteSimpleTableName($table->name) . ')';
        $indexes = $this->db->createCommand($sql)->queryAll();
        $uniqueIndexes = [];
        foreach ($indexes as $index) {
            $indexName = $index['name'];
            $indexInfo = $this->db->createCommand('PRAGMA index_info(' . $this->quoteValue($index['name']) . ')')->queryAll();
            if ($index['unique']) {
                $uniqueIndexes[$indexName] = [];
                foreach ($indexInfo as $row) {
                    $uniqueIndexes[$indexName][] = $row['name'];
                }
            }
        }
        return $uniqueIndexes;
    }