从 UPDATE 子查询调用 Oracle 关联数组给出 PLS-00201 错误

Question

我正在尝试从关联数组查找值以更新 table，但出现错误。这是演示该问题的最低限度代码（我的实际查询要复杂得多）。

我是不是遗漏了什么，或者如果这是 Oracle 的限制，是否有解决办法？

CREATE TABLE t_employee AS SELECT cast('john' as varchar2(30)) emp_name, CAST (NULL AS NUMBER (5)) emp_id FROM DUAL;
DECLARE
    TYPE emp_typ IS TABLE OF NUMBER INDEX BY VARCHAR2(30);
    emp_lookup   emp_typ;
BEGIN
    emp_lookup ('john') := 1234;
    UPDATE t_employee e
       SET emp_id = (SELECT emp_lookup (e.emp_name) FROM DUAL);
END;
/

--DROP TABLE t_employee;

> PLS-00201：必须声明标识符 'E.EMP_NAME'

当我将更新更改为更简单的构造时：

UPDATE t_employee SET emp_id = emp_lookup (t_employee.emp_name);

我发现这个问题：PLS-00382：表达式类型错误

同SELECT。在我看来，我们不能直接在 SQL 语句中使用关联数组。

Answer 1

关联数组集合是 PL/SQL 唯一的数据类型；它不能在 SQL 语句中使用。

来自Oracle documentation：

Table 5-1 PL/SQL: Collection Types

Collection Type	Number of Elements	Index Type	Dense or Sparse	Uninitialized Status	Where Defined	Can Be ADT Attribute Data Type
Associative array (or index-by table)	Unspecified	String or PLS_INTEGER	Either	Empty	In PL/SQL block or package	No
VARRAY (variable-size array)	Specified	Integer	Always dense	Null	In PL/SQL block or package or at schema level	Only if defined at schema level
Nested table	Unspecified	Integer	Starts dense, can become sparse	Null	In PL/SQL block or package or at schema level	Only if defined at schema level

...

An associative array (formerly called PL/SQL table or index-by table) is a set of key-value pairs.

...

Unlike a database table, an associative array:

• Does not need disk space or network operations
• Cannot be manipulated with DML statements

---

VARRAY 和嵌套的 table 集合可以在 SQL 语句中使用。