MySQL中的游标表达 [英] Cursor expression in MySQL

问题描述

如何实现与MySQL数据库（从5.6版本开始）中的Oracle游标表达式相同的功能？下面的
是对Oracle游标表达式的示例查询

How do I achieve the same as an Oracle cursor expression does in a MySQL database (version from 5.6 onwards) below is a sample query of an Oracle cursor expression

SELECT department_name, CURSOR(SELECT salary, commission_pct 
   FROM employees e
   WHERE e.department_id = d.department_id)
   FROM departments d;

如何使用MySQL数据库达到相同的目的？

How can I achieve the same as this with a MySQL database?

如果我在输出以下的oracle上执行此查询，则会产生
depart_name游标结果

if i execute this query on oracle below output i will be produced, depart_name cursor result

MCA { SALARY = 20000，COMMISSION_PCT = 2>，< SALARY = 40000，COMMISSION_PCT = 20>，}

BE {< SALARY = 20000，COMMISSION_PCT = 2>，}

推荐答案

我不知道 CURSOR是什么（）在oracle中使用是因为我从未接触过oracle，但我不知道它是否对您有帮助，但我认为您想像这样加入：

I don't know what a CURSOR() does in oracle because I've never touched oracle, but I don't know if it would help you but I think you wanted to join like this:

SELECT d.department_name, e.salary, e.commission_pct. 
FROM departments d
INNER JOIN employees e
ON (e.department_id = d.department_id);

我为您提供此链接以获取有关关节的更多信息：
https://sql.sh/cours/jointures
并根据sql.sh：

I give you this link for more information on joints: https://sql.sh/cours/jointures and according to sql.sh:

有几种方法可以将2个表关联在一起。以下是使用的各种技术的
列表：

There are several methods to associate 2 tables together. Here is the list of the different techniques that are used:

• 内部联接：内部联接当两个表中的条件都为true时返回记录。这是最常见的
  联接之一。


• CROSS JOIN：交叉联接使2张表的笛卡尔积。换句话说，允许将表的每一行与第二个表的每个
  行连接起来。注意，结果的数量通常是
  很高。


• LEFT JOIN（或LEFT OUTER JOIN）：：外部联接返回所有的记录即使未在另一张表中检查条件
  
  ，也要在左侧表中（LEFT = left）。


• RIGHT JOIN（或RIGHT OUTER JOIN）： 外部联接返回右侧表中的所有记录（RIGHT =右侧），即使未在另一个表中检查条件
  。


• FULL JOIN（或FULL OUTER JOIN）：外部联接，可在至少两个表之一满足条件时返回结果。


• SELF JOIN ：允许将一个表本身与另一个表联接。


• NATURAL JOIN：如果至少有两个表之间自然联接在两个SQL表之间具有相同名称的一列。


• UNION JOIN：联合的关节。

• INNER JOIN: internal join to return the records when the condition is true in both tables. This is one of the most common
  joins.
• CROSS JOIN: cross join to make the Cartesian product of 2 tables. In other words, allows to join each row of a table with each row of a second table. Attention, the number of results is generally very high.
• LEFT JOIN (or LEFT OUTER JOIN): external join to return all the records of the left table (LEFT = left) even if the condition is not
  checked in the other table.
• RIGHT JOIN (or RIGHT OUTER JOIN): External join to return all records in the right-hand table (RIGHT = right) even if the condition is not checked in the other table.
• FULL JOIN (or FULL OUTER JOIN) : external join to return the results when the condition is true in at least one of the 2 tables.
• SELF JOIN : allows to join a table with itself as if it were another table.
• NATURAL JOIN : natural join between 2 tables if there is at least one column with the same name between the 2 SQL tables.
• UNION JOIN: joint of union.

如果您有任何问题，我可以回答。

if you have any questions, I am available to answer them.

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