Multi-table 从子查询混淆中无条件取行

Question

INSERT ALL
 INTO sal_history (empid,hiredate,sal)
 VALUES (empid,hiredate,sal)
 INTO mgr_history (empid,mgr,sal)
 VALUES (empid,mgr,sal)
SELECT employee_id AS "EMPID",
       hire_date   AS "HIREDATE",
       salary      AS "SAL",
       manager_id  AS "MGR"
FROM   employees
WHERE  employee_id > 200;

insert into 子句如何知道在整个语句中哪些列select 用于插入多表sal_history 和mgr_history？如我所见，sal_history 中有 3 列，mgr_history 中有 3 列，但在子查询中有 4.

我知道这个语句是如何工作的，对于子查询中的每一行，"insert_into_clause" 只执行一次，但这不是重点，这只是我对列不了解的一件小事。

Answer 1

每个 INTO 子句指定要为该 table 填充哪些列，匹配的 VALUES 子句指定 来自子查询使用。在这种情况下，子查询使用相同的名称，这可能有点令人困惑；也许你会发现使用不同的别名更清楚：

INSERT ALL
 INTO sal_history (empid,hiredate,sal)
 VALUES (sub_empid,sub_hiredate,sub_sal)
 INTO mgr_history (empid,mgr,sal)
 VALUES (sub_empid,sub_mgr,sub_sal)
SELECT employee_id AS "SUB_EMPID",
       hire_date   AS "SUB_HIREDATE",
       salary      AS "SUB_SAL",
       manager_id  AS "SUB_MGR"
FROM   employees
WHERE  employee_id > 200;

VALUES 子句中使用了所有四个子查询列（别名）；每个三个，SUB_EMPID 和 SUB_SAL（带有我希望澄清的前缀）都出现在两者中。

Multi-table 从子查询混淆中无条件取行

Multi-table unconditional fetching rows from sub-query confusion

sql

oracle

oracle11g