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所在平台: Udemy |
课程主页: https://www.udemy.com/course/mastering-sql-table-joins-from-scratch-real-world-examples/
课程评论：没有评论
《精通SQL表连接：从零开始，真实世界案例解析》 本课程专注于SQL（结构化查询语言）中的核心概念——表连接（Table Joins）。SQL是一种用于管理关系型数据库信息（RDBMS）的特殊编程语言，其“关系型”的特性是通过表连接实现的，它允许用户将来自两个或多个表的数据链接到单个查询结果中。 课程中，我们将深入探讨不同类型的SQL表连接，并结合Oracle数据库环境进行语法演示和实践。主要涵盖的连接类型包括： * **INNER JOIN (内连接)**：根据指定的连接条件，仅返回两个表中匹配的行。 * **LEFT OUTER JOIN (左外连接)**：返回左表中的所有行，以及右表中匹配的行。如果右表中没有匹配，则结果中右表的列将显示为NULL。 * **RIGHT OUTER JOIN (右外连接)**：返回右表中的所有行，以及左表中匹配的行。如果左rowIndex中没有匹配，则结果中左表的列将显示为NULL。 * **CROSS JOIN (交叉连接)**：生成两个表的笛卡尔积，返回所有可能的行组合，通常没有显式的连接条件。 * **NATURAL JOIN (自然连接)**：基于两个表中同名列的隐含连接条件进行连接（内连接或外连接）。 课程还强调，无论哪种连接类型，都可以通过`ON`子句中的显式连接条件或`WHERE`子句中的额外条件来进一步限制和筛选结果。 本课程最大的亮点在于提供大量真实的、贴近实际应用场景的SQL表连接案例，帮助学习者在实践中掌握这些重要的数据库操作技能。
SQL is a special-purpose programming language designed for managing information in a relational database management system (RDBMS). The word relational here is key; it specifies that the database management system is organised in such a way that there are clear relations defined between different sets of data. Join makes relational database systems relational. Joins allow you to link data from two or more tables together into a single query result-from one single SELECT statement. .When combining rows from multiple tables in one query, you need to use the JOIN command. There are a few different types of joins, and the following should help explain the differences between them. The syntax will vary depending on which database type you are using. In this course i have used Oracle database. The JOIN operations, which are among the possible Table Expressions in a FROM clause, perform joins between two tables. Below is a brief description of the various types of joins used in Oracle. INNER JOIN operationSpecifies a join between two tables with an explicit join clause.LEFT OUTER JOIN operationSpecifies a join between two tables with an explicit join clause, preserving unmatched rows from the first table.RIGHT OUTER JOIN operationSpecifies a join between two tables with an explicit join clause, preserving unmatched rows from the second table.CROSS JOIN operationSpecifies a join that produces the Cartesian product of two tables. It has no explicit join clause.NATURAL JOIN operationSpecifies an inner or outer join between two tables. It has no explicit join clause. Instead, one is created implicitly using the common columns from the two tables. In all cases, you can specify additional restrictions on one or both of the tables being joined in outer join clauses or in the WHERE clause. In this course there will be lots of hands-on real world examples of SQL table joins.
