创建具有关系 SQL 的表

Question

I would like to know how relationships between tables are created.

I intend that when a new row is added to table1 that row is also created in table 2, how can I do this?

 Table1
 ID_Orders   ID_Line   Orders   Clients
    1          2        A       ABC
    2          2        B       ABC

 Table2
 ID_Orders   ID_Line   Product
    1          2        A       
    2          2        B 

  

I tried to use the foreign key relationship, but it is not working.

CREATE TABLE Table2(
 ID_Orders   int ,
 ID_Line   int,
 Product text,
 FOREIGN KEY(ID_Orders) REFERENCES Table1(ID_Orders),
 FOREIGN KEY(ID_Line) REFERENCES Table1(ID_Line)
 );

Answer 1

What you have described is not a standard relationship between two tables. Those relationships are described using foreign key relationships. But you want "automatic" updates.

The simplest method is to use a view:

create view table2 as
    select ID_Orders, ID_Line, Orders as Product
    from table1;

A variant on this is a materialized view , which would materialize the data, so queries might be faster (well, probably not in this case, but possibly if the query were more complicated).

An alternative is to have a bona fide table2 and using an insert (and perhaps update and delete triggers as well) on table1 . When a row is inserted into table1 then the trigger can copy data to table2 .

All that said, it is a bad practice to store the same data in multiple places. Sometimes, it can be an important optimization. But from what you describe, you don't need two tables.

Answer 2

I know it's the most lazy way but it worked:) thanks

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