The correct way is that if error code is HA_ERR_RECORD_FILE_FULL, then TemptableAggregateIterator::Init add create_ondisk_from_heap function, convert temptable to innodb disk temp table, then call table()->file->ha_index_read_map position cursor, finally execute table()->file->ha_update...
Re: Group By a date, show counts for last 7 days, return 0 if none raachachacha January 25, 2011 12:25PM Re: Group By a date, show counts for last 7 days, return 0 if none laptop alias January 17, 2011 05:19PM Sorry, you can't reply to this topic. It has been closed. ...
select student_id,max(borrow_time) as lastBorrowTime from borrow_books_record group by student_id ) br1 on br1.student_id=br.student_id and br1.lastBorrowTime = br.borrow_time 需求2: MySQL查询距离当前时间最近的一条数据 介绍 在实际的应用程序中,我们经常需要查询数据库中最接近当前时间的数据。
select job_id,max(salary) from employees where commission_pct is not null GROUP BY job_id HAVING max(salary)>6000 ORDER BY max(salary); #查询每个工种每个部门的最低工资,并按最低工资降序 select min(salary),job_id,department_id from employees GROUP BY job_id,department_id ORDER BY min(sal...
0 MYSQL数据库的基础:事务、锁 事务 事务的开启、提交、回滚 在默认情况下,用户执行的每一条SQL语句都会被当成单独的事务【自动提交】。 【开启事务】:如果要将一组SQL语句作为一个事务,则需要先执行以下语句显式地开启一个事务。 START TRANSACTION; -- 或 BEGIN; 【
record_type:0普通记录、1目录项、2最小记录、3最大记录#heap_no heap_no:由于每页会默认插入2条最小与最大记录,分别对应0,1。其他插入记录则从2开始计算#存储页中每组数据的总和记录 n_owned:页中每组记录的总和#next_record next_record:指向下一条记录的地址偏移量 ...
A record buffer cannot be used for reading BLOBs, which are stored outside of the record. The BLOB primary key was not detected when the record buffer was set up, as the primary key column was not yet in the read set. Retrievals ordered by row ID temporarily add the primary key at a...
using where:使用到where来过虑数据。不是所有的where clause都要显示using where.。如以=方式访问索引。 using tmporary:用到临时表。 using filesort:用到额外的排序.。(当使用order by v1,而没用到索引时,就会使用额外的排序)。 range checked for eache record(index map:N):没有好的索引。
Record lock:单个行记录上的锁 Gap lock:间隙锁,锁定一个范围,不包括记录本身 Next-key lock:record+gap 锁定一个范围,包含记录本身 相关知识点: innodb对于行的查询使用next-key lock Next-locking keying为了解决Phantom Problem幻读问题 当查询的索引含有唯一属性时,将next-key lock降级为record key Gap锁设计的...
⁶ 例如,范围检查查询计划会为JOIN中的每一行重新评估索引。你可以通过在EXPLAIN中的Extra列中查找“range checked for each record”来查看这个查询计划。这个查询计划还会增加Select_full_range_join服务器变量。 ⁷ 我们同意,一部没有演员的电影很奇怪,但 Sakila 示例数据库中没有列出Slacker Liaisons的演员,它描...