Test database downloaded on github. Index: explain select: query the scope of the date field of the employees table if you want to query the recruits in a certain period of time, 1. Why interpret the results, using the type field or ALL? What doe...
Boss, the following sentence SQL, the execution time has reached 6s, what should I do? in the end, I chose the scheme of "create a separate index " with the least impact. not sure this is the best result! just because of my environment, comprehens...
the problem I face now is I have a datasheet that is almost 1 million. it s not a way to go on like this. how can I separate it out, but I can still use the data from the datasheet? because suppose I export it to the drop table I can t use it ...
Why can mysql save time with varchar and still make time comparisons? What is the principle? Y-m-d H:i:s like this ...
the database currently has 1 million data (it has been running for about half a month) the following sentence takes 6 seconds to run (1 million results for where alone), and both user_id and time are indexed ...
MySQL,select uses in to query. There are about 5000 items in the collection after in. There are many records in this table. The fields in in query are indexed . the original SQL is similar to this SELECT a FROM table WHERE an in ( 1x code 2 ) and o...
I have seen a lot of articles on mysql indexes that say that if a field has a small range of values (a large number of duplicate values), there is no need to establish an index. but my actual test: user_type_id field has an index: then executi...
select fields from information_schema.COLUMNS where .... sqlsql ...
problem description 1.mysql in collection query is too inefficient and takes too long. the environmental background of the problems and what methods you have tried user_id and physicion are the user fields associated with this table. Because the s...
for example, select * from table limit 100 if there are 1 million data in the table, , then this statement will scan the whole table, filter out all the 1 million data that meets the requirements , and then fetch the first 1 million rows . and if you ...
use directly alter table order_log add outdated int default 0 null; it hasn t been over for a long time is there any way to speed it up? ...
problem description specific error message is General error: 1205 Lock wait timeout exceeded; try restarting transaction the reason for this problem is that there is a process that has been occupying the lock and does not release it. How do you repr...
CREATE DEFINER=`root`@`%` FUNCTION `is_mixed`(str1 TEXT, str2 TEXT) RETURNS tinyint(4) BEGIN DECLARE ismixed TINYINT DEFAULT 0; set ismixed:=(select concat(str1, , ) regexp concat(replace(str2, , , ,| ), , )); RETURN ismixed; EN...
During the interview today, the interviewer asked a question, table a 100W, table b 500W. If table an and table b are checked together, the query speed is very slow, how to optimize it? the interviewer said the index was perfect. I didn t answer at th...
problem description there is a user table with in it. uid regdate reg_package reg_channel ... now I have a SQL query for user data SELECT * FROM `user` ORDER BY `regdate` DESC LIMIT 0,50; there is a multi-column index on this table. i...
there are two tables Table 1: Student number 1 | Student number 2 | Student number 3 001 | 002 | 003 Table 2: Student number | name 001 | Zhang San 002 | Li Si 003 | Wang Wu desired results: student number 1 | name 1 | student number 2 | nam...
reason suppose I want to input all the data of a number table, how can I change the value of this field to B if there is A? INSERT INTO `wp_posts` (`ID`, `content`) VALUES (13335, <h3>< h3> r n[embed]https: www.instagram.com p Bc...
for example, ten thousand people vote for one person what I do is to read the number of votes first and then get the votes + 1 , but if ten thousand people vote at the same time, the number of votes and updates must be incorrect . The code is as foll...
basic information: The datasheet has almost 10 million pieces of data, using the mycat sublibrary. the indexes in the data table are PRIMARY id AppName (AppName, custidStatus, channel) the table creation statement is as follows CREATE TABLE...
problem description recently, I have been optimizing the related business of the system learn that you can improve the performance of db through thread pooling here comes the problem mysql has its own thread pool. You can add parameters such as ...