Db::getColumn() 

\nn\t3::Db()->getColumn($table = '', $colName = '', $useSchemaManager = false); 

Get a table column (TCA) for a specific table

\nn\t3::Db()->getColumn( 'tablename', 'fieldname' );
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@param string $table
@param string $colName
@param boolean $useSchemaManager
@return array

Source Code 

public function getColumn ( $table = '', $colName = '', $useSchemaManager = false )
{
	$cols = $this->getColumns( $table, $useSchemaManager );
	return $cols[$colName] ?? [];
}
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