Posts by Pantoja • 181 points
11 posts
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answer42
viewsA: Is it better to repeat field or Join to access the relationship?
The ideal is to use JOIN, because if you put the customer id in the VISIT table you will be creating a relation that is redundant, since you can get the same information using JOIN through the…
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votes3
answers422
viewsA: Update in the same table
About UPDATE, the other answers are ok and I agree that you are a little confused to understand. But just to clarify more: UPDATE TBL_AULA SET DATA_AULA = '2018-01-23' WHERE DATA = '2018-01-20';…
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votes1
answer689
viewsA: Academic ER "system" modeling
Take a look at this model: In the associative entity, an example of how to store the student’s history (just adapt to yours) is shown. For the student to see, simply assemble an SQL query after your…
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votes2
answers13959
viewsA: What is the difference between Associative Entity and the Intermediate Table of relationships N for N?
The intermediate relationship table N to N is the table generated in the conceptual-logical mapping of cardinalities N to N. Every relationship N:N generates a table in the mapping. The Associative…
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votes1
answer724
viewsA: Example and illustration about redundant relationships (MER)
Redundant relationships are those unnecessary ones that don’t need to exist for you to be able to come up with information. Analyzing the definition with a different reading, we have that if we…
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votes2
answers2246
viewsA: Doubt in class diagram
I would add the "book" method in "Room" taking into consideration "reservations made by an employee" and "make a room reservation for a customer".
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votes1
answer181
viewsA: MYSQL Sub-Query (SELECT MIN)
Use temporary tables. SELECT min(cod_remador) FROM (SELECT (clube.nome) AS clube, COUNT(remadores.cod_remador) AS n_remadores FROM clube, remadores WHERE clube.cod_clube=remadores.cod_clube GROUP BY…
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votes1
answer251
viewsA: Error in update sql: Subquery returned more than 1 value. This is not permitted when the subquery Follows
Does right: UPDATE cd_pro SET CustoLiquido = ((10 * CustoLiquido) / 100) + CustoLiquido WHERE id_marca = 1 As you want to do for the brand and you have the id_tag in the cd_pro table, you will not…
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votes6
answers4346
viewsA: What is the difference between attribute and field in the classes?
In object orientation we have the concept of Attributes, which are the characteristics that the class can have. When analyzing the literature (books, articles, scientific journals) we do not find…
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votes1
answer1091
viewsA: Performing UPDATE on ORACLE using FROM
The FROM clause is not accepted in the UPDATE command, hence the use of the IN clause in WHERE. Apparently, it is accepted in some Database Management Systems such as Postgre. But if we analyze the…
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votes1
answer337
viewsA: mysql query browser or mysql Workbench are SGBD?
Mysql Server is a Database Manager System (DBMS). Workbench is a visual tool for controlling server functionality. Workbench will only work if Mysql Server is properly installed. Same goes for Query…