怎么用一天sql 语句删除 主表信息和对应的从表信息?
--个人觉得
可以先在副表参照性约束加上 on delete cascade(级联删除)
再直接在主表中删除就可以了
Example
Let's look at an example of how to create a foreign key with cascade delete using the CREATE TABLE statement in Oracle/PLSQL.
For example:
CREATE TABLE supplier
( supplier_id numeric(10) >not null,
supplier_name varchar2(50) not null,
contact_name varchar2(50),
CONSTRAINT supplier_pk PRIMARY KEY (supplier_id)
);
CREATE TABLE products
( product_id numeric(10) not null,
supplier_id numeric(10) not null,
CONSTRAINT fk_supplier
FOREIGN KEY (supplier_id)
REFERENCES supplier(supplier_id)
ON DELETE CASCADE);
In this example, we've created a primary key on the supplier table called supplier_pk. It consists of only one field - the supplier_id field. Then we've created a foreign key called fk_supplier on the products table that references the supplier table based on the supplier_id field.
Because of the cascade delete, when a record in the supplier table is deleted, all records in the products table will also be deleted that have the same supplier_id value.
-- 创建外键(使用 ON DELETE CASCADE 选项,删除主表的时候,同时删除子表)
ALTER TABLE 学生表
ADD CONSTRAINT FK_学生班级
FOREIGN KEY (班级ID) REFERENCES 班级表 ON DELETE CASCADE;
也就是, 只要你那个外键, 是 ON DELETE CASCADE 的。
那么当你
DELETE FROM 班级表 WHERE 班级 = '一班' 的情况下。
数据库会自动把 外键关联的 一班下面的学生, 自动删除掉。
下面是一个模拟的例子:
-- 创建测试主表. ID 是主键.
CREATE TABLE test_main (
id INT NOT NULL,
value VARCHAR(10),
PRIMARY KEY(id)
);
-- 创建测试子表.
CREATE TABLE test_sub (
id INT NOT NULL,
main_id INT ,
value VARCHAR(10),
PRIMARY KEY(id)
);
-- 插入测试主表数据.
INSERT INTO test_main(id, value) VALUES (1, 'ONE');
INSERT INTO test_main(id, value) VALUES (2, 'TWO');
-- 插入测试子表数据.
INSERT INTO test_sub(id, main_id, value) VALUES (1, 1, 'ONEONE');
INSERT INTO test_sub(id, main_id, value) VALUES (2, 2, 'TWOTWO');
1> -- 创建外键(使用 ON DELETE CASCADE 选项,删除主表的时候,同时删除子表)
2> ALTER TABLE test_sub
3> ADD CONSTRAINT main_id_cons
4> FOREIGN KEY (main_id) REFERENCES test_main ON DELETE CASCADE;
5>
6> -- 测试删除主表数据. 将成功地执行.
7> DELETE
8> TEST_MAIN
9> WHERE
10> ID = 1;
11>
12> -- 测试检索子表,应该只有一条 main_id = 2 的数据.
13> SELECT
14> *
15> FROM
16> test_sub;
17>
18> go
(1 行受影响)
id main_id value
----------- ----------- ----------
2 2 TWOTWO
(1 行受影响)
delete 学生表 where ID in (x, xx, xxx)
delete 班级表 where ID in (x, xx, xxx)
首先,你要确任:
主从表是否存在外键关联;
外键级联关系(no action,set null,cascade等)如果外键设置的是cascade才可以一条删除,否则,没办法了