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...
const {injectBabelPlugin} = require ( react-app-rewired ); module.exports = function override (config, env) { config = injectBabelPlugin([ import , { libraryName: antd-mobile , style: css }], config); return config; }; I followed the steps ...
input, using weex wants to draw the underline as shown in the figure. At first, set the border attribute for input, which can be previewed by web, but it is not displayed on mobile phone. It is found that input does not support border attribute. Is ther...
the number of registered users is about 1000, and the number of online users is 50-100. the background database is connected with mongodb, which stores real-time captured twitter data, dynamic pages, small downloads and high security requirements. How t...
how can I return the value of isBol? if you write in this way, you can only return empty . ...
The usage of is similar to the following <app-list> <div>{{ item }}< div> < app-list> ...