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Primary key constraint
If you are asked to build a table, how do you determine its primary key?
What is the difference between a primary key constraint and a unique key constraint?
Primary key constraint: uniquely can confirm each field in the table. Every table must have at least one primary key.
Unique key constraint: When a column has a unique key constraint, it can only contain unique values, that is, the column cannot contain duplicate values. There can be no unique key in the table, but there must be a primary key.
If you already have a record of the primary key in your table. When you insert a record with the same primary key, an error will be reported in the table.
In DSO, if you set the overwrite data field value, the previous primary key record will be overwritten. There will never be two records with the same primary key. (This is also what you need to consider when building a watch)
The primary key must not be empty, and the unique key can be empty.
When we create a DSO, we must consider which ones are used as key fields and which ones are used as data fields.
How to debug start routine
In fact, when you create the conversion, the background has already built an ABAP code for you to cover all the mapping and rule details. Backstage? That's how it works.
The start, end, and expert routines you add can also be seen in the generated program.
This program is in the conversion interface: extras->display generated program
and then it will jump to an ABAP Editor: SE38,
a series of automatically generated report names, and a source code that cannot be changed.
If you have a start routine in your conversion:
there will be this start_routine, not limited to the following figure, is similar to this.
Double-click this start routine and it will go to the place where you wrote the method.
Set breakpoint
At the beginning of your code, make a breakpoint
Execute the debug mode of DTP
Simulation operation, expert mode should be selected.
In the filter filter, if you have a huge amount of data, you can set some conditions.
There are also some breakpoints that can be set.
Then click Execute.