In ABAP SQL, an alias is a temporary name that can be assigned to a field or a database table in a query. An alias can be used to make the query more readable, to avoid name conflicts, or to access fields or tables with long names.An alias is created with the AS keyword and is only valid for the duration of the query1.

The following are examples of how to assign an alias to a field or a database table in ABAP SQL:

B . field (from field list): A field is a column of a table or a view that contains data of a certain type. A field can be assigned an alias in the field list of a SELECT statement, which specifies the fields that are selected from the data source. For example, the following query assigns the alias name to the field carrname of the table scarr:

SELECT carrid, carrname AS name FROM scarr.

The alias name can be used instead of carrname in other clauses of the query, such as WHERE, GROUP BY, ORDER BY, and so on2.

C . database table: A database table is a collection of data that is organized in rows and columns. A database table can be assigned an alias in the FROM clause of a SELECT statement, which specifies the data source that is selected from. For example, the following query assigns the alias c to the table scarr:

SELECT c.carrid, c.carrname FROM scarr AS c.

The alias c can be used instead of scarr in other clauses of the query, such as WHERE, JOIN, GROUP BY, ORDER BY, and so on3.

The following are not valid for assigning an alias in ABAP SQL:

A . order criterion (from order by clause): An order criterion is a field or an expression that is used to sort the result set of a query in ascending or descending order. An order criterion cannot be assigned an alias in the ORDER BY clause of a SELECT statement, because the alias is not visible in this clause.The alias can only be used in the clauses that follow the clause where it is defined1.

D . group criterion (from group by clause): A group criterion is a field or an expression that is used to group the result set of a query into subsets that share the same values. A group criterion cannot be assigned an alias in the GROUP BY clause of a SELECT statement, because the alias is not visible in this clause.The alias can only be used in the clauses that follow the clause where it is defined1.

The correct ON condition that must be inserted in place of ''???'' is:

ON Sprojection.carrier_id=Z_Source2.carrier_id

This ON condition specifies the join condition between the CDS view Sprojection and the database table Z_Source2. The join condition is based on the field carrier_id, which is the primary key of both the CDS view and the database table.The ON condition ensures that only the records that have the same value for the carrier_id field are joined together1.

The other options are not valid ON conditions, because:

A . ON Z_Sourcel.camer_id = 7_Source2 carrier_id is not valid because Z_Sourcel and 7_Source2 are not valid data sources in the given code. There is no CDS view or database table named Z_Sourcel or 7_Source2. The correct names are Z_Source1 and Z_Source2. Moreover, the field camer_id is not a valid field in the given code. There is no field named camer_id in any of the data sources. The correct name is carrier_id.

B . ON Sprojection Camer=Source2 carrier_id is not valid because Sprojection and Source2 are not valid data sources in the given code. There is no CDS view or database table named Sprojection or Source2. The correct names are Sprojection and Z_Source2. Moreover, the field Camer is not a valid field in the given code. There is no field named Camer in any of the data sources. The correct name is carrier_id.Furthermore, the ON condition is missing the dot (.) operator between the data source name and the field name, which is required to access the fields of the data source1.

C . ON Sprojection. Carrier Source2.carrier is not valid because Carrier and carrier are not valid fields in the given code. There is no field named Carrier or carrier in any of the data sources. The correct name is carrier_id.Moreover, the ON condition is missing the dot (.) operator between the data source name and the field name, which is required to access the fields of the data source1.

Both statements are valid in ABAP, but they have different effects on the program.

##NEEDED is a pragma that can be used to hide warnings from the ABAP compiler syntax check. It tells the check tools that a variable or a parameter is needed for further processing, even if it is not used in the current statement.For example, if you declare a variable without assigning any value to it, you can use ##NEEDED to suppress the warning about unused variables12.

The pragma is not checked by the syntax checker means that you can use any pragma to hide any warning from the ABAP compiler syntax check, regardless of its effect on the program logic or performance.For example, if you use ##SHADOW to hide a warning about an obscured function, you can also use it to hide a warning about an invalid character in a string12.

You cannot do any of the following:

#EC_NEEDED is not checked by the syntax checker: This is not a valid statement in ABAP.There is no pseudo-comment with #EC_NEEDED in ABAP3.

The pseudo-comment is checked by the syntax checker: This is false. Pseudo-comments are obsolete and should no longer be used in ABAP.They were replaced by pragmas since SAP NW 7.0 EhP2 (Enhancement Package)4.

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 following are the explanations for each statement:

A: This statement is valid. go_ifl may call method ml with go_ifl->ml(). This is because go_ifl is a data object of type REF TO ifl, which is a reference to the interface ifl. The interface ifl defines a method ml, which can be called using the reference variable go_ifl. The class cll implements the interface ifl, which means that it provides an implementation of the method ml. The data object go_ifl is assigned to a new instance of the class cll using the NEW operator and the inline declaration operator @DATA.Therefore, when go_ifl->ml() is called, the implementation of the method ml in the class cll is executed123

B: This statement is valid. Instead of go_cll = NEW #(...) you could use go_ifl = NEW cll(...). This is because go_ifl is a data object of type REF TO ifl, which is a reference to the interface ifl. The class cll implements the interface ifl, which means that it is compatible with the interface ifl. Therefore, go_ifl can be assigned to a new instance of the class cll using the NEW operator and the class name cll. The inline declaration operator @DATA is optional in this case, as go_ifl is already declared.The parentheses after the class name cll can be used to pass parameters to the constructor of the class cll, if any123

E: This statement is valid. go_ifl may call method m2 with go_ifl->m2(...). This is because go_ifl is a data object of type REF TO ifl, which is a reference to the interface ifl. The class cll implements the interface ifl, which means that it inherits all the components of the interface ifl. The class cll also defines a method m2, which is a public method of the class cll. Therefore, go_ifl can call the method m2 using the reference variable go_ifl. The method m2 is not defined in the interface ifl, but it is accessible through the interface ifl, as the interface ifl is implemented by the class cll.The parentheses after the method name m2 can be used to pass parameters to the method m2, if any123

The other statements are not valid, as they have syntax errors or logical errors. These statements are:

C: This statement is not valid. go_cll may call method ml with go_cll->ifl~ml(). This is because go_cll is a data object of type REF TO cll, which is a reference to the class cll. The class cll implements the interface ifl, which means that it inherits all the components of the interface ifl. The interface ifl defines a method ml, which can be called using the reference variable go_cll. However, the syntax for calling an interface method using a class reference is go_cll->ml(), not go_cll->ifl~ml(). The interface component selector ~ is only used when calling an interface method using an interface reference, such as go_ifl->ifl~ml().Using the interface component selector ~ with a class reference will cause a syntax error123

D: This statement is not valid. Instead of go_cll = NEW #() you could use go_ifl = NEW #(...). This is because go_ifl is a data object of type REF TO ifl, which is a reference to the interface ifl. The interface ifl cannot be instantiated, as it does not have an implementation. Therefore, go_ifl cannot be assigned to a new instance of the interface ifl using the NEW operator and the inline declaration operator @DATA. This will cause a syntax error or a runtime error.To instantiate an interface, you need to use a class that implements the interface, such as the class cll123