Re: Select first record of each ID mysql5.6 Peter Brawley December 17, 2020 10:43AM Re: Select first record of each ID mysql5.6 Dave F December 17, 2020 12:01PM Re: Select first record of each ID mysql5.6 Peter Brawley December 17, 2020 12:12PM ...
如果SQL 是查询语句(select 语句),MySQL 就会先去查询缓存( Query Cache )里查找缓存数据,看看之前有没有执行过这一条命令,这个查询缓存是以 key-value 形式保存在内存中的,key 为 SQL 查询语句,value 为 SQL 语句查询的结果。 如果查询的语句命中查询缓存,那么就会直接返回 value 给客户端。如果查询的语句没有...
-- SELECT * FROM test.tb_student WHERE 1=1 and id='2' LIMIT 1 FOR UPDATE; -- 可以获取到 id = '2' 的锁-- 不论 会话窗口1 先开启的事务无论是否有 commit 或 rollback ,查询 id !='1' 的行数据时,因没有被加行锁,会立即返回数据SELECT*FROMtest.tb_studentWHERE1=1andid='1'LIMIT1F...
$r = mysql_query("SELECT * FROM user WHERE country = 'China'"); if (mysql_num_rows($r) > 0) { // ... } // 有效率的: $r = mysql_query("SELECT 1 FROM user WHERE country = 'China' LIMIT 1"); if (mysql_num_rows($r) > 0) { // ... } 1. 2. 3. 4. 5. 6. ...
( 'admin', '123456'); Query OK, 2 rows affected (0.00 sec) Records: 2 Duplicates: 0 Warnings: 0 MariaDB [bbs]> select * from users; +---+---+---+---+ | id | password | username | img_path | +---+---+---+---+ | 1 | 123456 | ajest | NULL | | 2 | 123456 ...
{ "total_record": 1, "slow_log_list": [ { "count": "1", "time": "1.04899 s", "lock_time": "0.00003 s", "rows_sent": "0", "rows_examined": "0", "database": "mysql", "users": "root", "query_sample": "INSERT INTO time_zone_name (Name, Time_zone_id) VALUES (N...
The record parameter is specified as [option1 = value1, option2 = value2...] or [Query = "select ..."] for example. Feedback Was this page helpful? YesNo Provide product feedback| Ask the community Additional resources Training
set_source_partition_id() : mysql::binlog::event::Rows_event::Extra_row_info set_sp_cache_version() : sp_head set_sp_current_parsing_ctx() : LEX set_space_id() : DDL_Record, lob::ref_t, Tablespace, undo::Tablespace set_space_id_no_redo() : lob::basic_page_t, lob::z_data...
那么这里可以解析为代码运行到mysql_lock_tables函数的末尾之前的所有的时间都记录到utime_after_lock时间中,实际上并不精确。但是实际上MDL LOCK的获取和MyISAM表锁的获取都包含在里面。所以即便是select语句也会看到Lock_time并不为0。下面是栈帧: 代码语言:javascript ...
As shown in the above picture, we have used the feature of inserting multiple rows in the table as explained in the previous section. The first record was inserted with the CURRENT_DATE() function. This function returns the current system date. The second record was inserted with a particular...