其他优化策略 exist和in的区别
选择的标准:小表驱动大表
SELECT *FROM A WHERE cc IN (SELECT cc FROM B)SELECT *FROM A WHERE EXISTS (SELECT cc FROM B WHERE B.ccA.cc)当A小于B时,用EXISTS。因为EXISTS的实现,相当于外表循环࿰…
关联查询优化 数据准备
#分类
CREATE TABLE IF NOT EXISTS type(
id INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
card INT(10) UNSIGNED NOT NULL,
PRIMARY KEY ( id )
);#图书
CREATE TABLE IF NOT EXISTS book(bookid INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,cardINT(10…