json_encode非常慢,我能做些什么才能让它更快?

I used json_encode for more than one associative tables and fields so it will make more than 600.000records to store, but the loading needs more than 11second to done, and in my case I need it to be just 1second. What should I do? I inserted this variable to javascript in my html file. var a = <?php echo json_encode(qry_x());?>;
the qry_x is a function that provide mysql query to select all the tables that I need. But when I limit the record to 30records, it just need 1second to load, but when I don't give it limit, it need 11seconds and more to load. The size of the table I want to show is just 2MB.
This is the query:
SELECT a.kd_food, a.nm_food, a.type, a.kd_each, c.nm_pereach, a.garnice, b.type1, b.type2, b.type3, b.type4, b.type5, b.type6, a.typeavg, a.price1, a.price2, a.price3, a.price4, a.price5, a.price6, a.price7 FROM foods AS a LEFT JOIN b AS place ON (a.kd_food=b.kd_food AND b.kd_place=001) LEFT JOIN pereach AS c ON a.kd_each=c.kd_each ORDER BY a.nm_food;