CREATE TABLE students ( id INT PRIMARY KEY, name VARCHAR(50) NOT NULL, age INT NOT NULL ); 然后,向这个表格中插入数据:INSERT INTO students (id, name, age) VALUES (1, 'Alice', 18), (2, 'Bob', 19), (3, 'Charlie', 20); 最后,使用以下 SQL 语句将Alice 的记录删除:...
building_no INT NOT NULL, FOREIGN KEY (building_no) REFERENCES buildings (building_no) ON DELETE CASCADE )ENGINE=InnoDB DEFAULT CHARSET=utf8; 注意:在外键约束定义的末尾添加ON DELETE CASCADE子句。 第三步, 将一些数据插入到buildings表,如下插入语句: INSERT INTO buildings(building_name,address) VALUES...
department_idINT);-- 插入示例数据INSERTINTOdepartments (department_name)VALUES('HR'), ('Engineering');INSERTINTOemployees (first_name, last_name, department_id)VALUES('John','Doe',1), ('Jane','Smith',2), ('Jim','Brown',NULL); 要删除employees表中department_id为NULL的记录,可以使用以下语...
The DELETE statement in SQL can delete multiple rows by specifying a condition that matches more than one row. Example: CREATE TABLE orders (order_id INT PRIMARY KEY,customer_id INT,status VARCHAR(50));INSERT INTO orders (order_id, customer_id, status) VALUES(101, 1, 'Pending'),(102, ...
(order_id, customer_name) VALUES (1, 'Alice'); INSERT INTO order_items (item_id, order_id, product_name) VALUES (1, 1, 'Product A'); INSERT INTO order_items (item_id, order_id, product_name) VALUES (2, 1, 'Product B'); -- 删除订单及其相关订单项 DELETE FROM orders WHERE ...
SQL CREATETABLEdbo.Table1 (ColAintNOTNULL, ColBdecimal(10,3)NOTNULL); GOCREATETABLEdbo.Table2 (ColAintPRIMARYKEYNOTNULL, ColBdecimal(10,3)NOTNULL); GOINSERTINTOdbo.Table1VALUES(1,10.0), (1,20.0);INSERTINTOdbo.Table2VALUES(1,0.0); GODELETEdbo.Table2FROMdbo.Table2INNERJOINdbo.Table1ON(...
name}, </if> <if test="item.age != null"> age=#{item.age} </if> </set> WHERE id=#{item.id}; </foreach> </update> 控制台sql语句: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 Preparing: UPDATE mutest.student SET name=?, age=? WHERE id=?; UPDATE mutest.student SET...
INSERT INTO course VALUES('03' , '英语' , '03'); --3条记录 SELECT count(1) FROM cours...
索引不应该使用在含有大量的 NULL 值的列上。 索引不应该使用在频繁操作的列上。 1、很少在查询中使用的列 2、含有很多重复数据的列,比如只有0,1,这时候扫描整表通常会更有效。 3、TEXT,IMAGE的列不应该创建索引。这些字段长度不固定,或许很长,或许为空。
mysql tables in use 1, locked 1 7 lock struct(s), heap size 1136, 3 row lock(s), undo log entries 4 MySQL thread id 300, OS thread handle 140425969882880, query id 5479930 172.18.70.114 root update insert into session_endpoint (...) values (...) ...