What do the dots mean in this SQL query?

Question

I'm new to MySQL. Can anyone describe lines below which I get theme from the demo of the jqgrid, what is the meaning of a.id? What is the meaning of these dots?

$SQL = "SELECT a.id, a.invdate, b.name, a.amount,a.tax,a.total,a.note FROM invheader a, clients b WHERE a.client_id=b.client_id ORDER BY $sidx $sord LIMIT $start , $limit";

You can find the example here: http://trirand.com/blog/jqgrid/jqgrid.html in the advanced>Multi select

Answer 1

You've asked several questions here. To address the dots:

In the FROM clause, a is used as an alias for the invheader table. This means you can reference that table by the short alias a instead of the full table name.

Therefore, a.id refers the the id column of the invheader table.

It is generally considered bad practice to simply give your tables the aliases a, b, c, etc. and I would recommend you use something more useful.

I suggest you read some basic MySQL tutorials as this is a fundamental principal.