Re: [PHP] Are left joins more efficient?

THese are very different things, generally. The first join is an INNER
join. It pulls all records that have the matching ids. The left join
is an OUTER join. It pulls ALL records from table1, and any matching
records from table2. This is useful if you want customer and address
info, but want all customers, regardless of whether they have addresses
or not.

They are very different.

If you are actually meaning to ask about whether this

SELECT * FROM table1,table2 WHERE table1.id=table2.id;

is better or worse than (note the lack of LEFT)

SELECT * FROM table1 JOIN table2 ON table1.id=table2.id;

then that is dependent on your database. I can't comment on MySQL, but
PostgreSQL, for instance, will usually optimize the second query better.
But it is highly dependent on what you're doing and where you're doing it.

HTH.
Pete.


anachronism@mengelt.com wrote, On 2003/Aug/25 10:59 AM:
> Hello,
>
> I program for a website that gets massive loads of traffic. Optimisation has
> become an important issue lately.
>
> At the moment, all queries on the website follow the same format when
> joining tables:
> SELECT * FROM table1,table2 WHERE table1.id=table2.id;
>
> My question is, would this format be more efficient?
> SELECT * FROM table1 LEFT JOIN table2 ON table1.id=table2.id;
>
> Over the last couple of years I have read and heard two different answers.
> Years ago it was said that doing Left Joins are faster and more efficient.
> But with recent updates to MySQL I have read that both queries are broken
> down and optimised the same way by MySQL.
>
> Any thoughts? I havn't come across any comparisons on the web, so any
> answers would be appreciated.
>
> (couldn't find any mysql specific groups so i'm posting in the next best
> thing!)
>
> Thanks
>
> -Dennis
>
>
>
>
>