Question

我是SQL新手，不了解如何从表中删除行。我有这个：

select distinct course.course_id, title, dept_name, credits
from course, section
where course.course_id not in (select course_id from section);

当这个运行时我得到了行： BIO-399 "Computational Biology" Biology 4

现在，如何从“课程”表中删除它？我无法搜索此特定类，因为此代码需要能够在具有不同类的任何表上工作。

我试过

delete from course where course_id in
   (select distinct course.course_id, title, dept_name, credits
   from course, section
   where course.course_id not in (select course_id from section));

但这不起作用。它说“操作数应该包含1列”，但我想删除一行而不是列。我已经看了几个类似问题的答案，并试图模仿答案，但我没有运气。

Answer 1

您可以使用加入SQL的概念来尝试此操作。在这里，我们将使用左连接。

delete course from 
course left join section on course.course_id = section.course_id 
where course.course_id = NULL;

注意：这里我假设course_id在两个表中都存在，就像外键一样，如果不是，为了更清晰，你能否共享两个表的模式？

希望这有帮助

Answer 2

试试这个：

delete from course where course_id in
(select distinct course.course_id
from course, section
where course.course_id not in (select course_id from section));

根据我的理解，您无需加入此查询的课程和部分。

请尝试这一点，看看你是否得到了相同的结果：

select distinct course.course_id
from course
where course.course_id not in (select course_id from section)

如果是，则使用此查询删除：

delete from course where course_id in
(select distinct course.course_id
from (select * from course) as c
where c.course_id not in (select course_id from section));

Answer 3

您的SQL应该是这样的

DELETE FROM `course` WHERE `course_id`="BIO-399" AND `title`="Computational Biology" AND `credits` ="4";

细分：

Delete from table-name where condition

上面将删除表table-name中满足where子句

之后提供的条件的行

条件为column-name = value。

Answer 4

DELETE 
FROM course 
WHERE course_id="BIO-399" AND title = "Computational Biology" AND credits ="4";

Answer 5

MariaDB [sandbox]> drop table if exists school_course,school_section;
Query OK, 0 rows affected (0.19 sec)

MariaDB [sandbox]> create table school_course (id int, name varchar(2));
Query OK, 0 rows affected (0.23 sec)

MariaDB [sandbox]> create table school_section(id int, cid int, name varchar(2));
Query OK, 0 rows affected (0.20 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> insert into school_course values (1,'c1'),(2,'c2');
Query OK, 2 rows affected (0.02 sec)
Records: 2  Duplicates: 0  Warnings: 0

MariaDB [sandbox]> insert into school_section values (1,1,'s1');
Query OK, 1 row affected (0.05 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> select sc.*, ss.*
    -> from school_course sc
    -> left join school_section ss on ss.cid = sc.id;
+------+------+------+------+------+
| id   | name | id   | cid  | name |
+------+------+------+------+------+
|    1 | c1   |    1 |    1 | s1   |
|    2 | c2   | NULL | NULL | NULL |
+------+------+------+------+------+
2 rows in set (0.00 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> delete sc
    -> from school_course sc
    -> left join school_section ss on ss.cid = sc.id
    -> where ss.cid is null;
Query OK, 1 row affected (0.05 sec)

MariaDB [sandbox]>
MariaDB [sandbox]> select sc.*, ss.*
    -> from school_course sc
    -> left join school_section ss on ss.cid = sc.id;
+------+------+------+------+------+
| id   | name | id   | cid  | name |
+------+------+------+------+------+
|    1 | c1   |    1 |    1 | s1   |
+------+------+------+------+------+
1 row in set (0.00 sec)

SQL从表中删除选定的行

5 个答案: