framework/db/oci/Schema.php
protected function getTableSequenceName($tableName)
    {
        $sequenceNameSql = <<<'SQL'
SELECT
    UD.REFERENCED_NAME AS SEQUENCE_NAME
FROM USER_DEPENDENCIES UD
    JOIN USER_TRIGGERS UT ON (UT.TRIGGER_NAME = UD.NAME)
WHERE
    UT.TABLE_NAME = :tableName
    AND UD.TYPE = 'TRIGGER'
    AND UD.REFERENCED_TYPE = 'SEQUENCE'
SQL;
        $sequenceName = $this->db->createCommand($sequenceNameSql, [':tableName' => $tableName])->queryScalar();
        return $sequenceName === false ? null : $sequenceName;
    }
protected function getTableSequenceName($tableName)
    {
        $sequenceNameSql = <<<'SQL'
SELECT
    UD.REFERENCED_NAME AS SEQUENCE_NAME
FROM USER_DEPENDENCIES UD
    JOIN USER_TRIGGERS UT ON (UT.TRIGGER_NAME = UD.NAME)
WHERE
    UT.TABLE_NAME = :tableName
    AND UD.TYPE = 'TRIGGER'
    AND UD.REFERENCED_TYPE = 'SEQUENCE'
SQL;
        $sequenceName = $this->db->createCommand($sequenceNameSql, [':tableName' => $tableName])->queryScalar();
        return $sequenceName === false ? null : $sequenceName;
    }
Sequence name of table.

@param string $tableName
@internal param \yii\db\TableSchema $table->name the table schema
@return string|null whether the sequence exists