Using ABAP SQL, the select statement that selects the mat field on line #17 is:

SELECT mat FROM demo_sales_cds_so_i_ve...

This statement selects the mat field from the CDS view demo_sales_cds_so_i_ve, which is defined on line #1. The CDS view demo_sales_cds_so_i_ve is a projection view that projects the fields of the CDS view demo_sales_cds_so_i, which is defined on line #2. The CDS view demo_sales_cds_so_i is a join view that joins the fields of the database table demo_sales_so_i, which is defined on line #3, and the CDS view demo_sales_cds_material_ve, which is defined on line #4. The CDS view demo_sales_cds_material_ve is a value help view that provides value help for the material field of the database table demo_sales_so_i.The mat field is an alias for the material field of the database table demo_sales_so_i, which is defined on line #91.

The other options are not valid because:

A . SELECT mat FROM Material... is not valid because Material is not a valid data source in the given code. There is no CDS view or database table named Material.

C . SELECT mat FROM demo_sales_so_i... is not valid because demo_sales_so_i is not a valid data source in the given code. There is no CDS view named demo_sales_so_i, only a database table. To access a database table, the keyword TABLE must be used, such as SELECT mat FROM TABLE demo_sales_so_i...

D . SELECT mat FROM demo sales cds material ve... is not valid because demo sales cds material ve is not a valid data source in the given code. There is no CDS view or database table named demo sales cds material ve. The correct name of the CDS view is demo_sales_cds_material_ve, with underscores instead of spaces.

The following are the explanations for each action:

A: Renaming a field in a structure that is included in the table definition causes an indirect change to the database table, as the field name in the table is derived from the structure. This change requires a table conversion, as the existing data in the table must be copied to a new table with the new field name, and the old table must be deleted.

B: Changing the field labels of a data element that is used in the table definition does not cause an indirect change to the database table, as the field labels are only used for documentation and display purposes. This change does not require a table conversion, as the existing data in the table is not affected by the change.

C: Deleting a field from a structure that is included in the table definition causes an indirect change to the database table, as the field is removed from the table as well. This change requires a table conversion, as the existing data in the table must be copied to a new table without the deleted field, and the old table must be deleted.

D: Shortening the length of a domain used in a data element that is used in the table definition causes an indirect change to the database table, as the field length in the table is derived from the domain. This change requires a table conversion, as the existing data in the table must be checked for compatibility with the new field length, and any data that exceeds the new length must be truncated or rejected.

The RESTful Application Programming feature that is used to ensure the uniqueness of a semantic key is determination. A determination is a type of behavior implementation that defines a logic that is executed automatically when certain events occur, such as create, update, delete, or activate. A determination can be used to calculate or derive values for certain fields, such as semantic keys, based on other fields or external sources. A determination can also be used to check the uniqueness of a semantic key by comparing it with the existing values in the database or the transaction buffer. A determination can use the ABAP SQL or the EML syntax to access and manipulate data. A determination can be defined using the DETERMINE action clause in the behavior definition of a CDS view entity or a projection view.A determination can also be annotated with the @ObjectModel.determination annotation to specify the event, the timing, and the scope of the determination12

The other RESTful Application Programming features are not used to ensure the uniqueness of a semantic key, but have different purposes and effects. These features are:

Validation: A validation is a type of behavior implementation that defines a logic that is executed automatically when certain events occur, such as create, update, delete, or activate. A validation can be used to check the consistency and correctness of the data, such as mandatory fields, data types, value ranges, or business rules. A validation can use the ABAP SQL or the EML syntax to access and manipulate data. A validation can be defined using the VALIDATE action clause in the behavior definition of a CDS view entity or a projection view.A validation can also be annotated with the @ObjectModel.validation annotation to specify the event, the timing, and the scope of the validation12

Action: An action is a type of behavior implementation that defines a logic that is executed explicitly by the user or the application. An action can be used to perform a specific business operation, such as creating, updating, deleting, or activating an entity instance, or triggering a workflow or a notification. An action can use the ABAP SQL or the EML syntax to access and manipulate data. An action can be defined using the ACTION clause in the behavior definition of a CDS view entity or a projection view.An action can also be annotated with the @ObjectModel.action annotation to specify the name, the description, the parameters, and the visibility of the action12

The statement that can be used to change the contents of a row of data in an internal table is MODIFY table. The MODIFY table statement can be used to change the contents of one or more rows of an internal table, either by specifying the table index, the table key, or a condition. The MODIFY table statement can also be used to change the contents of a database table, by specifying the table name and a work area or an internal table. The MODIFY table statement can use the TRANSPORTING addition to specify which fields should be changed, and the WHERE addition to specify which rows should be changed.

The other statements are not suitable for changing the contents of a row of data in an internal table, as they have different purposes and effects. These statements are:

APPEND table: This statement can be used to add a new row of data to the end of an internal table, either by specifying a work area or an inline declaration. The APPEND table statement does not change the existing rows of the internal table, but only increases the number of rows by one.

INSERT table: This statement can be used to insert a new row of data into an internal table, either by specifying the table index, the table key, or a sorted position. The INSERT table statement does not change the existing rows of the internal table, but only shifts them to make room for the new row. The INSERT table statement can also be used to insert a new row of data into a database table, by specifying the table name and a work area or an inline declaration.

UPDATE table: This statement can be used to update the contents of a database table, by specifying the table name and a work area or an internal table. The UPDATE table statement can use the SET addition to specify which fields should be updated, and the WHERE addition to specify which rows should be updated. The UPDATE table statement does not affect the internal table, but only the corresponding database table.

The nested join is evaluated from the top to the bottom in the order of the ON conditions. This means that the join expression is formed by assigning each ON condition to the directly preceding JOIN from left to right. The join expression can be parenthesized implicitly or explicitly to show the order of evaluation. In this case, the implicit parentheses are as follows:

SELECT * FROM (a INNER JOIN (b INNER JOIN c ON b~c = c~c) ON a~b = b~b)

This means that the first join expression is b INNER JOIN c ON b~c = c~c, which joins the columns of tables b and c based on the condition that b~c equals c~c. The second join expression is a INNER JOIN (b INNER JOIN c ON b~c = c~c) ON a~b = b~b, which joins the columns of table a and the result of the first join expression based on the condition that a~b equals b~b. The final result set contains all combinations of rows from tables a, b, and c that satisfy both join conditions.