SQLite is an Embeddable SQL Database Engine [1] and offers already a PHP extension [2]. Even if it has some limitations, there are at least already Subselects available. See the most simple example:
[aloha]# sqlite test.db
SQLite version 2.8.0
Enter \”.help\” for instructions
sqlite> create table tbl1(one varchar(10), two smallint);
sqlite> insert into tbl1 values(\’hello!\’,10);
sqlite> insert into tbl1 values(\’goodbye\’, 20);
sqlite> select * from tbl1;
hello!|10
goodbye|20
sqlite>
SQLite version 2.8.0
Enter \”.help\” for instructions
sqlite> create table tbl1(one varchar(10), two smallint);
sqlite> insert into tbl1 values(\’hello!\’,10);
sqlite> insert into tbl1 values(\’goodbye\’, 20);
sqlite> select * from tbl1;
hello!|10
goodbye|20
sqlite>
[1] http://www.hwaci.com/sw/sqlite
[2] http://sf.net/projects/sqlite-php
