我无法从具有外部连接的视图进行更新

Question

我正在使用 MySQL 了解 SQL，当我尝试从具有外部连接的视图进行更新时遇到问题

这是一个例子：

DROP TABLE IF EXISTS t1;
CREATE TABLE IF NOT EXISTS t1 (
  id tinyint(3) UNSIGNED NOT NULL AUTO_INCREMENT,
  t2_id tinyint(3) UNSIGNED DEFAULT NULL,
  col3 varchar(255) NOT NULL,
  PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO t1 (id, t2_id, col3) VALUES
(1, 1, 'a'),
(2, 1, 'b'),
(3, 2, '3'),
(4, 2, '7'),
(5, NULL, '!');

DROP TABLE IF EXISTS t2;
CREATE TABLE IF NOT EXISTS t2 (
  id tinyint(3) UNSIGNED NOT NULL AUTO_INCREMENT,
  col2 varchar(255) NOT NULL,
  PRIMARY KEY (id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO t2 (id, col2) VALUES
(1, 'Character'),
(2, 'Number');

CREATE OR REPLACE
VIEW v_t1_details
AS SELECT t1.id, t2.col2, t1.col3
FROM t1
LEFT JOIN t2 ON t1.t2_id = t2.id;

我在 MySQL 5.7（5.7.14 和 5.7.19，在两个版本之间完全卸载并重新安装），这是我使用此查询时发生的情况：

UPDATE v_t1_details SET col3 = 'c' WHERE id = 2;

#1288 - The target table v_t1_details of the UPDATE is not updatable

我知道不能对插入请求使用外连接，但我在我的课程或 MySQL 更新文档中没有看到类似的东西，所以我想知道为什么它不起作用。

感谢您的宝贵时间。

Answer 1

您无法更新 SQL VIEW - 一般来说

https://en.wikipedia.org/wiki/View_(SQL)

In a database, a view is the result set of a stored query on the data, which the database users can query just as they would in a persistent database collection object. This pre-established query command is kept in the database dictionary. Unlike ordinary base tables in a relational database, a view does not form part of the physical schema: as a result set, it is a virtual table computed or collated dynamically from data in the database when access to that view is requested.

https://www.codeproject.com/Tips/639239/Creating-and-Usage-of-View-in-SQL

A view is virtual, the data from a view is not stored physically. It is a set of queries that, when applied to one or more tables, is stored in the database as an object. A view encapsulates the name of the table. A virtual table contains column and data from multiple tables.

但多亏了@Thibaut，事实上你可以使用 mySQL 但有一定的限制

https://dev.mysql.com/doc/refman/5.7/en/view-updatability.html

With respect to insertability (being updatable with INSERT statements), an updatable view is insertable if it also satisfies these additional requirements for the view columns:

There must be no duplicate view column names.

The view must contain all columns in the base table that do not have a default value.

The view columns must be simple column references. They must not be expressions, such as these:

我无法从具有外部连接的视图进行更新

I can't update from a view with an outer join

mysql

join

outer-join

sql-view