Explain a SELECT statement for MySQL

someone can explain me what this query does?

$sql=mysql_query("SELECT b.id, b.data FROM data_parent a, data b WHERE b.id=a.did and parent='$id'");

it works but honestly i didn't unde开发者_运维百科rstand.

Thanks

1. Take the table data_parent and alias it as a.
2. Take the table data and alias it as b.
3. Match values in a with those in b on the id column in b and the did column in a.
4. Filter for rows in [some table since it isn't specified] such that the column parent is equal to some passed in value.
5. From those results, display the id and data columns from b

The query grabs the COlumns ID & Data from the Data table where the data_parentID is the same as the data table id. And it is based on for 1 parent ID