problem description this kind of business is involved in the development. My idea is as follows: polymorphic association is used. This structure is particularly troublesome, relying on code implementation, and requires better solutions. has a course ...
how to deal with fields with unique indexes in the case of sub-tables? there is no guarantee of constraints when adding new ones ...
such as the title. even if it can reduce data inconsistencies, it cannot be completely eliminated. Is there any other way to compensate for ? Or what? ...
seniors, I want to splice the existing fields and fill them in the new fields, such as original table < table > < thead > < tr > < th > id < th > < th > name < th > < th > date < th > < th > record_id < th > < tr > < thead > < tbody > < tr...
< H1 > problem description < H1 > has the following data: WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 }) this time the elements in this array are deleted correctly. < H1 > final question < H1 > WH...
problem description Design a purchase, sale and inventory system for a medium-sized multi-store seller; in order to improve sales opportunities and reduce the production of expired goods, items will be transferred back and forth among multiple stores...
about career development ...
for example, the information in the database cannot be bound. I tried to pass a database object to the constructor of the class bound to ObservableList (called student), and then when I constructed the student object, I called the add method in the datab...
select I. I. ID. I. Price. I. Amount. Name from orderitem i, goods g where order_id =? And i.goods_id = g.id java.sql.SQLException: Cannot create com.yanzi.model.OrderItem: com.yanzi.model.OrderItem Query: select I.id from orderitem i, goods g where or...
there is data in every table, but it is 112KB and there is no .frm file. What is this all about? ...
data structure, graph, single linked list storage problem. ...
Navicat is connected to the database of the real server and has all the permissions to add, delete, modify and check. First ask the bosses if there is any way not to change the permissions of users in the database on the server side, but to limit their p...
Table relationship: question: how to query the data shown in the figure using native sql statements? expected data structure (the list item of the product appears as a nested object): { "category": [ { "id": 1,...
use leftJoin multi-table join lookup. Finally, a field in select is a field from count in one of the right tables, but if there is no count data in that table, the entire query will lose the result. Now you want to keep the data in the left table if the...
question: query all data whose RUN_TYPE is 1 and SWITCH_TYPE is 1 in adjacent time (RUN_DATE) of ID. data sheet: Tunable data, as shown in the figure. :RUN_TYPE1SWITCH_TYPE1IDRUN_DATE SQL:SELECT * FROM T_DATA a WHERE a.SWITCH_TYPEIN( 1 ) AND (a...
the database system is installed on the host in the local area network, which can only be accessed and used in the local area network. How to use holer to access the database in the internal network from the external network? https: github.com wisdom-...
question: select * from table where created_at > where is the problem? How to solve? answer: time writes dead, closes, time opens, there must be closing time. The question is, why should it be a closed interval when querying this time field? It ...
found an interesting problem with timestamp after the mysql5.6 version, as follows: mysql> desc test_idx; +--------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------+-...
< H2 > Database design of encyclopedic websites < H2 > as shown in the figure above, it is a medical encyclopedia website. For example, the typical symptoms page is full of text with large p tags. I don t know how to store them in the database. If...
The table structure before is like this 2 sql4alias_namealias_name2alias_name3 ...
if($url = www.xxx.com ){ header( HTTP 1.1 301 Moved Permanently ); header( Location: $target_url); } the above code, 301 redirect has been accessed in the browser, and the browser will remember that it is permanently redirected. Will direc...
-- axios , that I introduced through cdn -- but in Firefox, my request will be blocked. Has anyone ever encountered this situation? --optionchromeIE : ...
react uses for conditional rendering. { this.state.show ? <View > : null } the content is rendered only when the condition is triggered, otherwise it is not rendered and is not controlled by display:none . at a time like this, how do you ...
the with statement is used in the development process, and the webpack cannot be compiled the reason is that strict mode cannot use with , but how to close strict mode ? webpack :4.8.3 babel :6.26.3 in addition, the babel-plugin-transform-remo...
Project to achieve three-tier distribution; rebate to all superiors (up to three levels) after database design and user registration but I don t have a clue. Please give me a thought. if it is directly registered to reward 20 yuan if it is throug...