B+树总是会保持平衡。但是为了保持平衡对于新插入的键值可能需要做大量的拆分页(split)操作;部分情况下可以通过B+树的旋转来替代拆分页操作,进而达到平衡效果。 B+树的删除 B+树使用填充因子(fill factor)来控制树的删除变化,50%是填充因子可设的最小值。B+树的删除操作同样必须保证删除后叶子节点中的记...
InnoDB 支持事务,支持行级别锁定,支持 B-tree、Full-text 等索引,不支持 Hash 索引; MyISAM 不支持事务,支持表级别锁定,支持 B-tree、Full-text 等索引,不支持 Hash 索引; Memory 不支持事务,支持表级别锁定,支持 B-tree、Hash 等索引,不支持Full-text 索引; NDB 支持事务,支持行级别锁定,支持 Hash 索引,...
我们来说几个特殊的情况,select * from student where name = "张三" age>18 and address="北京" and class="三班" ,在这种情况下,后两列其实都没有用到索引,可以自己脑补一下索引的B+tree自己琢磨一下。 留一个思考题,为什么我们在建表的时候需要设置字段不为空。 索引优化的路还很长,后面我会详细的...
> scans, the number of primitive scans is hard to predict, and quite > indicative of what's really going on with the scan. *googles nbtree SAOP scans and finds the very helpful[1]* Yes, I feel like this should definitely be part of the ANALYZE output. Seeing how Lukas has to look...
1)BTREE:B+树索引 2)HASH：HASH索引 3)FULLTEXT：全⽂索引 4)RTREE：R树索引 图1·B+tree索引 图2·B*tree索引 3.索引管理 索引建⽴在表的列上(字段)的。在where后⾯的列建⽴索引才会加快查询速度。pages<---索引（属性）<---查数据。1、索引分类：主键索引 普通索引*** 唯⼀索引 2、添加...
I don't want A to to be the plan, while showing B' to the user, as the performance picture for the two may be completely different. And, as I mentioned upthread, the differences between AMs in the (lack of) meaning in index column order also makes it quite wrong to generally ...
each tree) were packaged in aluminum foil, labeled by sex and date, and immediately frozen in liquid nitrogen. They were then stored at -80 °C until use. Other flower samples were scanned for morphological analysis and then oven-dried and ground for the nutrient and physiological analyses....
1A2). However, b presents a form similar to a capital S in association with P and s. Overall, the combined positive processes regulating the PSRR are dominant at the rising section of the humped PSRR, but combined negative processes act after the intermediate P level, forming the humped ...
SELECT e.ENAME,a.HISAL FROM EMP e INNER JOIN SALGRADE a ON e.SAL BETWEEN a.LOSAL AND a.HISAL; 1. 2.3内连接之自连接 SELECT a.ENAME,b.ENAME FROM EMP a INNER JOIN EMP b ON a.MGR=b.EMPNO; 1. 3.外连接 selec … from …left join …on ...
索引文件具有 B-Tree 的最左前缀匹配特性,如果左边的值未确定,那么无法使用此索引。 2.3 计算、函数导致索引失效 举例: student表的字段stuno上设置有索引 CREATE INDEX idx_sno ON student(stuno); 索引优化失效: EXPLAIN SELECT SQL_NO_CACHE id, stuno, NAME FROM student WHERE stuno+1 = 900001; ...