SHOW VARIABLES LIKE ‘long_query_time%’; 或者通过set session long_query_time=1来改变当前session变量; 记录慢SQL并后续分析 查询当前系统中有多少条慢查询记录 配置版 【mysqld】下配置: slow_query_log=1; slow_query_log_file=/var/lib/mysql/atguigu-slow.log long_query_time=3; log_output=FILE ...
类图(配置项关联) usesUser+username: StringQuery+execute(query: String) 调试步骤 在实际应用中,调试SUBSTRING功能可能会遇到各种问题,以下是调试步骤的详细说明。 日志分析 通过分析MySQL的日志,可以定位到问题,特别是当查询没有返回预期结果时。 有序列表(带折叠块的高级技巧) 检查查询语法是否正确 确保SUBSTRING的...
SUBSTRING_INDEX(str,delim,count) 语法格式说明 str:需要操作的字符串 delim:分隔符 count:匹配 delim 出现的次数,可正数可负数 栗子一 代码语言:javascript 代码运行次数:0 运行 AI代码解释 SELECTSUBSTRING_INDEX('www.mysql.com','.',1);# wwwSELECTSUBSTRING_INDEX('www.mysql.com','.',-1);# comSELEC...
I've migrated a db (and query) from a DB2 server to a MySql server. I had a query: "SELECT * FROM item, author WHERE item.i_a_id = author.a_id AND item.i_title LIKE 'my_search_string' ORDER BY item.i_title FETCH FIRST 50 ROWS ONLY" A person suggested me to convert it ...
1 row in set (0.00 sec) mysql> The following query returns the initial character of firstname from employees table mysql> select SUBSTRING(firstname,1,1),lastname from employees; +---+---+ | SUBSTRING(firstname,1,1) | lastname | +---...
方法二:group_concat—— 同一分组内的值先连接,再选取;#[Err] 1140 - In aggregated query without GROUP BY, expression #1,使用group_concat必须用group by selectcourse, group_concat(scoreorderbyscoredesc)assc #连接的是排序字段fromt_variablegroupbycourse #分组字段 ...
The query returns the full name of each publisher (pub_name) and a 5-character substring starting from the 4th character of pub_name, but only for publishers based in the USA. Output: mysql> SELECT pub_name, SUBSTRING(pub_name,4,5) -> FROM publisher -> WHERE country='USA'; +---+...
1 row in set (0.02 sec) Visual depiction: Example of MySQL SUBSTRING_INDEX() function using negative count This MySQL query extracts the substring located to the right of the second delimiter (.) in the string 'www.mytestpage.info'. The counting commences from the right end of the string...
mysql> set @str = "abcdxyz"; Query OK, 0 rows affected (0.00 sec) mysql> select @str; +---+ | @str | +---+ | abcdxyz | +---+ 1 row in set (0.00 sec) mysql> select length(@str); +---+ | length(@str) | +---+ | 7 | +---+ 1 row in set (0.01 sec) mysql...
The second subquery then takes the above 2 numbers and takes them away to return the number of characters that the string's position is in from the right. Which then allows the right function to be used to return everything on the right of the start of the string. Then it locates the...