doubts about subqueries and table join queries there are two tables, user (user) and user_dictionary (user Dictionary), and then my colleague struggles with me with a problem. Forgive me for this scum who doesn t know . related codes user: industr...
when querying, you need to query the scope according to the time field, timestamp type. Statement does not have subqueries, associated queries, only look up this table. it takes about 4.5 seconds to find 50, 000 results. This field has been indexed, bu...
< H1 > question < H1 > the data table needs a column to keep the current time, and then it needs to be accurate to milliseconds , and then search it. It is found that datetime can take decimals. According to this blog TIMESTAMP(3) DATETIME(3)3 T...
when there are too many SQL pages (for example, limit 1000000,20), the efficiency will be significantly reduced. How to optimize it? Here, take mysql as an example ...
I have a table exchange CREATE TABLE `exchange` ( `id` int(11) NOT NULL AUTO_INCREMENT, `rank` int(11) NOT NULL, `name` varchar(255) NOT NULL, `volume` varchar(255) NOT NULL, `timestamp` datetime NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB...
if the table table has a federated index (sex, id) and id itself is the primary key , does the following sql go to the index? select * from table where sex= m order by id limit 1000000,10 my feeling is that according to the execution order of sql ...
has such a logic, a piece of data, if there is in the database, then update, if it does not exist, then insert. But now there are ten thousand. So how to accomplish the task efficiently? ...
now I have an array, which contains about 100000 of the data, all personId,. I now need to use this ID to query other data in another table. Is there any good way to make the query more efficient? Whether IN can be used or not, although it is easy to wri...
such as the title. see that MySQL generates a tree for the primary key, and the leaf node holds the row data corresponding to the primary key. The secondary index leaf node holds the value of the primary key. excuse me: does the leaf node of th...
I would like to ask the gods, the speed of unwritten-out writing is fast, or the speed of logged-out is fast, why? now it is a joint check of two tables, and the amount of data is small. If there is a large amount of data, which method is more advantag...
has always thought that index optimization is effective in where is useless in select but it seems that there is a performance difference between select nonclustered index columns, clustered index columns, unindexed columns and select *? ...
refer to antd s custom scheme, introduce babel-plugin-import and react-app-rewired, and add .bablrc file, but not successfully is it necessary to eject? how to make create-react-app support stage-0, without eject? ...
is there any way for the parent component to pass parameters to the underlying child components? it does not need to be passed level by level, and it does not use readuX ....
can t watch cousera video and can t open lectrue slide. Is there a solution? ...
as shown in the figure, the backup command did not return a result. It has been more than 20 minutes . ...
server { listen 80; -sharp server_name localhost; -sharp index index.html; charset utf-8; -sharp root data static; -sharp location { autoindex on; -sharp autoindex_exact_size o...