Comprehensive and Detailed Explanation from Exact Extract:
* from_mixed converts a mixed-case string into uppercase with a chosen separator between words.
* Given input ‘LorelpsumFactum’, the function splits at uppercase letters, uppercases the parts, and joins them with _.
* Output: LORE_IPSUM_FACTUM.
* condense only removes extra spaces, to_upper only changes case, and to_mixed does the reverse of from_mixed.
Study Guide Reference: ABAP Keyword Documentation – String Functions (from_mixed, to_mixed).

Comprehensive and Detailed Explanation From Exact Extract:
Parameters in CDS view entities (WITH PARAMETERS) must always be supplied when querying. In ABAP SQL, the syntax rules are:
* A. CorrectSupplying a literal date (‘20230101’) directly is valid because the parameter p_date is of type abap.dats.
* B. CorrectSupplying a value via an ABAP expression using @( … ) is syntactically correct. Here, cl_abap_context_info=>get_system_date( ) returns the current system date in ABAP Cloud-compliant way, and is wrapped with @() for expression embedding. This is the best practice in ABAP Cloud development.
* C. IncorrectBackticks (`…`) are used in ABAP for string templates, not for literals in this context. A date literal must be in quotes ‘…’.
* D. Incorrect:$session.system_date is not valid in ABAP SQL. Session variables like $session.* are supported in HANA SQL, but in ABAP CDS view consumption via ABAP SQL, this is not allowed.
Therefore, only A and B are correct.
Reference:ABAP CDS Development User Guide – section on CDS View Entity Parameters and ABAP SQL parameter passing rules; ABAP Cloud development guidelines on cl_abap_context_info=>get_system_date.

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.

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.

Secondary keys are additional keys that can be defined for internal tables to optimize the access to the table using fields that are not part of the primary key. Secondary keys can be either sorted or hashed, depending on the table type and the uniqueness of the key. Secondary keys have the following characteristics1:
A . Secondary keys must be chosen explicitly when you actually read from an internal table. This means that when you use a READ TABLE or a LOOP AT statement to access an internal table, you have to specify the secondary key that you want to use with the USING KEY addition. For example, the following statement reads an internal table itab using a secondary key sec_key:
READ TABLE itab USING KEY sec_key INTO DATA(wa).
If you do not specify the secondary key, the system will use the primary key by default2.
B . Multiple secondary keys are allowed for any kind of internal table. This means that you can define more than one secondary key for an internal table, regardless of the table type. For example, the following statement defines an internal table itab with two secondary keys sec_key_1 and sec_key_2:
DATA itab TYPE SORTED TABLE OF ty_itab WITH NON-UNIQUE KEY sec_key_1 COMPONENTS field1 field2 sec_key_2 COMPONENTS field3 field4.
You can then choose which secondary key to use when you access the internal table1.
D . Sorted secondary keys do NOT have to be unique. This means that you can define a sorted secondary key for an internal table that allows duplicate values for the key fields. A sorted secondary key maintains a predefined sorting order for the internal table, which is defined by the key fields in the order in which they are specified. For example, the following statement defines a sorted secondary key sec_key for an internal table itab that sorts the table by field1 in ascending order and field2 in descending order:
DATA itab TYPE STANDARD TABLE OF ty_itab WITH NON-UNIQUE SORTED KEY sec_key COMPONENTS field1 ASCENDING field2 DESCENDING.
You can then access the internal table using the sorted secondary key with a binary search algorithm, which is faster than a linear search3.
The following are not characteristics of secondary keys for internal tables, because:
C . Hashed secondary keys do NOT have to be unique. This is false because hashed secondary keys must be unique. This means that you can only define a hashed secondary key for an internal table that does not allow duplicate values for the key fields. A hashed secondary key does not have a predefined sorting order for the internal table, but uses a hash algorithm to store and access the table rows. For example, the following statement defines a hashed secondary key sec_key for an internal table itab that hashes the table by field1 and field2:
DATA itab TYPE STANDARD TABLE OF ty_itab WITH UNIQUE HASHED KEY sec_key COMPONENTS field1 field2.
You can then access the internal table using the hashed secondary key with a direct access algorithm, which is very fast.
E . Secondary keys can only be created for standard tables. This is false because secondary keys can be created for any kind of internal table, such as standard tables, sorted tables, and hashed tables. However, the type of the secondary key depends on the type of the internal table. For example, a standard table can have sorted or hashed secondary keys, a sorted table can have sorted secondary keys, and a hashed table can have hashed secondary keys1.

Comprehensive and Detailed Explanation From Exact Extract:
* In ABAP, structure component access uses the hyphen (-): structure-component. The other tokens are used for different purposes: -> for object reference attributes, => for static components, and / is not a field selector in ABAP.
* ABAP Cloud stresses typed APIs and static checks, ensuring misuse of component selectors is caught early; correct structure access with – is part of the enforced style.

Comprehensive and Detailed Explanation from Exact Extract:
* A. Automatic execution # # A constructor (CONSTRUCTOR) is automatically invoked when an instance of a class is created.
* B. Importing parameters # # Constructors can have importing parameters to initialize the object with values.
* C. First method called by client # # Not correct, because constructors are called by the system, not the client explicitly.
* D. Returning parameters # # Constructors cannot return values; they only set up the object.
This behavior is consistent across ABAP Cloud OOP classes, ensuring encapsulated initialization logic.
Verified Study Guide Reference: ABAP Objects Guide – Class Constructors and Instance Constructors.