游标(cursor)是Oracle系统在内存中开辟的一个工作区,在其中存放SELECT语句返回的查询结果。,PL/SQL隐式建立并自动管理这一游
为什么要Oracle游标:
先看这个:
这个SELECT语句可能返回多条记录,所以这个赋值语句可能是错误的。所以游标可以发挥作用了。
什么是游标?
游标(cursor)是Oracle系统在内存中开辟的一个工作区,在其中存放SELECT语句返回的查询结果。
游标的分类:
隐式游标:PL/SQL隐式建立并自动管理这一游标。隐式游标也叫做SQL游标。 对于SQL游标,不能对其显式地执行OPEN、CLOSE和FETCH语句,,但是可以使用游标属性从最近执行的SQL语句中获取信息。
显式游标:由程序员显式说明及控制,用于从表中取出多行数据,并将多行数据一行一行单独处理。
隐式游标:
隐式游标属性:
隐式游标举例:
返回所删除行的数量
显式游标:由用户显式声明,查询返回多行记录
更多Oracle相关信息见Oracle 专题页面 ?tid=12

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The MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.

MySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.

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MySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen

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