SQL injection, php and queueing multiple statement

Is there a switch (php side or pg side) to avoid things like:

pg_query("select id from table1 where a=$i");

into becoming

pg_query("select id from table1 where a=1 and 1=1; do something
nasty; -- ");

So that every
pg_query(...) can contain no more than one statement?

thanks

--
Ivan Sergio Borgonovo
http://www.webthatworks.it