Navicat 11.0.10版本
结果证明表关联比子查询速度更快
1.子查询:0.287s
SELECT sw,sh,cx,cy, (SELECT buy_url FROM b_product WHERE single_file_id = sys_item_id AND deleted = 0) AS buy_url, (SELECT discount_price FROM b_product WHERE single_file_id = sys_item_id AND deleted = 0) AS price, (SELECT price FROM b_product WHERE single_file_id = sys_item_id AND deleted = 0) AS old_price, (SELECT id FROM b_product WHERE single_file_id = sys_item_id AND deleted = 0) AS product_id, CONCAT('single_',sys_item_id) AS id FROM app_polly_file_item WHERE file_id=829 AND type='sys' AND sys_item_type='single' ORDER BY sys_item_id
2.表关联:0.176s
SELECT apfi.sw,apfi.sh,apfi.cx,apfi.cy, bp.buy_url, bp.discount_price AS price, bp.price AS old_price, bp.id AS product_id, CONCAT('single_',sys_item_id) AS id FROM app_polly_file_item apfi INNER JOIN b_product bp ON apfi.sys_item_id = bp.single_file_id AND bp.deleted=0 WHERE apfi.file_id=829 AND apfi.type='sys' AND apfi.sys_item_type='single' ORDER BY apfi.sys_item_id
更多sql优化参考:http://www.cnblogs.com/eva_2010/articles/2047558.html