Delete a Single RecordWrite a SQL query to delete a single record from a table based on a specific condition.Solution:-- Delete the employee with EmployeeID = 4. DELETE FROM Employees -- Specify the table to delete from. WHERE EmployeeID = 4; -- Delete only the employee wi...
A scalar subquery always returns only one value. It will be used to delete rows based on a condition derived from another table. Delete the book written by the most recently added author. It will be efficient in MySQL. Example: CREATE TABLE authors (author_id INT PRIMARY KEY,name VARCHAR(...
TimeId Command Argument//Time:2025-05-11T10:33:05.581135Z//User@Host: root[root] @ localhost [::1] Id:10//Query_time:5.002170Lock_time:0.000000Rows_sent:1Rows_examined:0SETtimestamp=1746959585;selectsleep(5); 上面日志解读如下: User@Host:表示用户和慢查询的连接地址(root 用户,localhost地址,...
const rows:5 filtered:1.00 Extra:Using index condition;Using where;Using filesort 1rowinset,1 warning (0.00 sec) # 执行用时 5 rows in set(0.01 sec) 其中: ・key_len: 160,表明联合索引的两个字段都用到了,(32+20) * 3
There are two forms of delete operations based on what is specified in the WHERE clause: Searched deletes specify a search condition to qualify the rows to delete. For example, WHEREcolumn_name=value. Positioned deletes use the CURRENT OF clause to specify a cursor. The delete operation occur...
| id | select_type | table | type | possible_keys | key | rows | Extra| key_len | +---+---+---+---+---+---+---+---+---+---+ | 1 | SIMPLE | o | ALL | idx_user_time | NULL | 1987400 | Using where; Using filesort | | 1 | SIMPLE |...
Using index condition:MySQL5.6之后新增的ICP,using index condtion就是使用了ICP(索引下推),在存储引擎层进行数据过滤,而不是在服务层过滤,利用索引现有的数据减少回表的数据。 3、show profile 分析 了解SQL执行的线程的状态及消耗的时间。 默认是关闭的,开启语句“set profiling = 1;” ...
There are two forms of delete operations based on what is specified in the WHERE clause: Searched deletes specify a search condition to qualify the rows to delete. For example, WHEREcolumn_name=value. Positioned deletes use the CURRENT OF clause to specify a cursor. The delete operation occur...
Delete Orders where orderid=1 If the where clause condition is false, it does not remove any rows. For example, we removed the ordered 1 from the orders table. If we execute the statement again, it does not find any rows to satisfy the where clause condition. In this case, it returns...
"filesort_priority_queue_optimization":{// 是否启用优先级队列"limit":102,// 排序后需要取的行数,这里为 limit 100,2,也就是100+2=102"rows_estimate":24576,// 估计参与排序的行数"row_size":123,// 行大小"memory_available":32768,// 可用内存大小,即设置的sort buffer大小"chosen":true// 是否...