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? ...
take MySQL as an example, what is the difference (principle and efficiency) between in and exists and between not in and not exists? What about using indexes? Say that not in and < > will not use indexes, won t you? ...
The index is a data structure in which the leaf node of the b + tree holds pointers to the actual rows. what about clustered indexes? what does InnoDB s clustered index mean by storing B+Tree indexes and data rows in the same structure? Does mean that...
EXPLAIN SELECT s.id, s.name, s.price, s.unit, s.qty, s.remark, s.image, s.cuft, s.volume, s.status, s.vender_id AS venderId, s.booth_id AS boothId, s.booth_no AS boothNo, s.show_booth_no AS showBoothNo, s.name_en AS nameEn, ...
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...
from the previous week to now, I found a problem: when the whole network accesses the url address, it always gets stuck somewhere, and the page cannot be loaded. Later, F12 called up the console and found that there was an abnormal js file access. At th...
the official account of Wechat fetches the (Baidu, Gaode) map on the mobile phone. ...
import SockJS from sockjs-client ; import Stomp from stompjs ; connection() { this.socket = new SockJS( http: 192.168.6.67:8081 endpoint ); this.stompClient = Stomp.over(this.socket); ...
when the width of the content in body exceeds the width of body due to the setting of left,margin thank you, and the width of body is not as wide as the width of the content, how to make the width of body equal to the width of the complete content? ...
problem description the website made of laravel is placed on the pagoda, but the entry file has been tampered with all the time. Try to find loopholes, delete many Trojans with the suffix PHP in the directory, and turn on the filter of pagoda nginx an...