(If you think this type of query is somewhat silly, note that it is the same question you might ask in the context of a business database to identify clients to whom you need to send out birthday greetings in the current week or month, for that computer-assisted personal touch.) You...
end repeat;commit;end $$ delimiter;--雇员表CREATETABLE`EMP`(`empno`int(6)unsigned zerofillNOTNULLCOMMENT'雇员编号',`ename`varchar(10)DEFAULTNULLCOMMENT'雇员姓名',`job`varchar(9)DEFAULTNULLCOMMENT'雇员职位',`mgr`int(4)unsigned zerofillDEFAULTNULLCOMMENT'雇员领导编号',`hiredate`datetimeDEFAULTNULL...
创建一个数据表 名为 前缀sites 数据表里有以下字段 site_id 整数型不为空的主键 url varchar 255 title varchar 255 short_desc text indexdate date spider_depth 整数型 默认为2 required text disallowed text can_leave_domain bool
{ "msg-type": "activity", "date": "1574932159871", "thread-id": "9", "query-id": "129", "user": "root", "priv_user": "root", "ip": "", "host": "localhost", "connect_attrs": { "_os": "linux-glibc2.12", "_client_name": "libmysql", "_pid": "6004", "_client_v...
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name (create_definition,...) [table_options] [partition_options] CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)] [table_options] [partition_options] [IGNORE | REPLACE] [AS] query_expression CREATE [TEMPORARY] ...
查看记录中第一条SQL详细时间:show profile for query 1; 2. 通过type指定显示其他信息 我们看一下官方提供的profile语法: SHOW PROFILE [type [, type] ... ] [FOR QUERY n] [LIMIT row_count [OFFSET offset]] type: { ALL 显示所有信息
一、理解MySQL的Query Optimizer MySQL Optimizer是一个专门负责优化SELECT 语句的优化器模块,它主要的功能就是通过计算分析系统中收集的各种统计信息,为客户端请求的Query 给出他认为最优的执行计划,也就是他认为最优的数据检索方式。 二、Query 语句优化基本思路和原则 ...
{"join_execution":{"select#":1,"steps":[{"creating_tmp_table":{// 创建临时表"tmp_table_info":{"table":"intermediate_tmp_table","row_length":13530,"key_length":0,"unique_constraint":false,"location":"memory (heap)",// 临时表位于内存"row_limit_estimate":1240}}},{"converting_tmp...
ALTER TABLE `table2` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci; ... 复制这些语句并逐个执行。 6. 修改所有字段的排序规则 生成修改所有字段的 SQL 语句(注意字符集和排序规则的位置): SELECT CONCAT( 'ALTER TABLE `', TABLE_NAME, '` MODIFY `', COLUMN_NAME, '` ', ...
Query_ID 表示自动分配的查询ID,顺序递增。Duration 表示SQL语句执行耗时Query 表示SQL语句内容 然后,我们再使用Query_ID去Profile中查看具体每一步的耗时情况: show profile for query 1; 可以清楚的看到耗时主要花在创建排序索引(Creating sort index)上面。 再试一条SQL: select distinct name from user; 这次的耗...