SQL SERVER on master-slave table trigger design

There are two two tables, A and B relationship is a master-slave table.
A table has two fields, date and number.
Table B has four fields of date and specification and number and quantity.
The number field of the two tables is an association relationship.

Currently A's data is triggered from other tables.Then add table B according to the data of table A.(It means that there is a load of goods in table A, and I want to slowly classify table B), and then the next step I need is to summarize the data in table B into table C by date and specification, and there must be two summaries,One label is injected into the library, and the other is labeled out of the library.

I have tried to write triggers in table B, but if table B adds a record, table C will add one, so it is unrealistic and can only be written in table A.

At present, I don't know if the data of table B is summarized in table A and inserted into table C, someone can give me some ideas on how to write it?