MySQL 中的光标表达式

Question

如何实现与 Oracle 游标表达式在 MySQL 数据库（从 5.6 开始的版本）中相同的效果下面是 Oracle 游标表达式的示例查询

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 数据库实现与此相同的目的？

如果我在 oracle 上执行此查询，将生成以下输出， depart_name游标结果

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

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

Answer 1

我不知道 CURSOR() 在 oracle 中做了什么，因为我从未接触过 oracle，但我不知道它是否对你有帮助，但我认为你想这样加入：

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

我给你这个 link 有关关节的更多信息： https://sql.sh/cours/jointures 并根据 sql.sh:

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

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。

MySQL 中的光标表达式

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