#2. mysql中的primary key,unique,联合唯一也都是索引,这些索引除了加速查找以外,还有约束的功能 2、MySQL常用的索引 普通索引INDEX:加速查找 唯一索引:-主键索引PRIMARYKEY:加速查找+约束(不为空、不能重复)-唯一索引UNIQUE:加速查找+约束(不能重复) 联合索引:-PRIMARYKEY(id,name):联合主键索引-UNIQUE(id,name)...
唯一索引:-主键索引PRIMARYKEY:加速查找+约束(不为空、不能重复)-唯一索引UNIQUE:加速查找+约束(不能重复) 联合索引:-PRIMARYKEY(id,name):联合主键索引-UNIQUE(id,name):联合唯一索引-INDEX(id,name):联合普通索引 索引的操作 添加主键索引: 创建的时候添加: 添加索引的时候要注意,给字段里面数据大小比较小的字...
Nelson, J. Growth mechanisms to explain the primary and secondary habits of snow crystals. Phil. Mag. A 81, 2337-2373 (2001).Nelson, J.: Growth mechanisms to explain the primary and secondary habits of snow crystals. Philos. Mag. A, 81, 2337-2373 (2001)...
Primary pollutants are those that are directly emitted from a source, such as sulfur dioxide from a power plant. Secondary pollutants are formed in the environment as a result of chemical reactions between primary pollutants, such as ground-level ozone formed from nitrogen oxides and volatile organi...
s1 WHERE id > 5890 AND order_note = 'a';从执行计划的key列中可以看出来，该查询使用 PRIMARY...
EXPLAIN SELECT * FROM s1 WHERE id > 5890 AND order_note = 'a'; 从执行计划的key列中可以看出来,该查询使用 PRIMARY索引来执行查询,从rows列可以看出满足id > 5890的记录有5286条。执行计划的filtered列就代表查询优化器预测在这5286条记录中,有多少条记录满足其余的搜索条件,也就是order_note = 'a'这个...
It is a collection of storage cells together with associated circuits needed to transfer information in and out of storage. There are two types of computer memory: Primary memory and secondary memory. RAM and ROM are termed as primary memory. Hard disk, floppy disk, ...
Explain the difference between primary and secondary pollutants.搜索 题目 Explain the difference between primary and secondary pollutants. 答案 解析 null 本题来源 题目:Explain the difference between primary and secondary pollutants. 来源: 环境工程英语试题及答案 收藏 反馈 分享...
The primary market is where securities for exchange are formulated and introduced to the public, whereas the secondary market (commonly known as the...Become a member and unlock all Study Answers Start today. Try it now Create an account Ask a question Our experts can answer your tough ...
2.Secondary Replica Set Role: Secondary replicas are copies of the primary, and they maintain an exact replica of the data from the primary node. Reads: By default, secondary nodes do not accept write operations. However, read operations can be routed to them using specific read...