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...
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problem description [AVAssetWriterInput markAsFinished] Cannot call method when status is 0. the environmental background of the problems and what methods you have tried po status = 1; related codes Please paste the code text below (do not r...
css error of asynchronously loaded components packaged by webpack4 I ve tried allChunks:true, but I can t parse it . related codes const path = require ( "path "); const ExtractTextPlugin = require ( extract-text-webpack-plugin ); module.expo...
topic description enter a number n as the qualification standard, and then enter a series of numbers, each time you enter a line break, the empty line wrap ends, and the qualified rate is output. pass rate refers to the ratio of qualified elements to...
jquery checks whether the data in the form has changed. If you don t find any change, you don t need to save the data. If you change, you can save it. Is there such a plug-in, or what is the idea ?...