子查询和联表查询哪个效率高? 执行速度:联接(Join) >> 子查询(Subquery) 内存占用:联接(Join) >> 子查询(Subquery) 子查询的分类 标量子查询( Scalar Subquery ) SELECT c_custkey FROM CUSTOMER WHERE 1000000 < ( SELECT 2023-07-13 数据库 #MySQL
MySQL实现防止重复插入 FROM DUAL实现防止重复插入 INSERT INTO qrdish_store_collect (tenant_id,store_id,user_id) SELECT #{tenantId},#{storeId},#{userId} FROM DUAL WHE 2023-07-12 数据库 #MySQL