The internal table type that allows both unique and non-unique keys is the standard table. A standard table has an internal linear index that can be used to access the table entries. The key of a standard table is always non- unique, which means that the table can contain duplicate entries. However, the system does not check the uniqueness of the key when inserting new entries, so the programmer can ensure that the key is unique by using appropriate logic. A standard table can be accessed either by using the table index or the key, but the response time for key access is proportional to the table size.
The other two internal table types, sorted and hashed, do not allow non-unique keys. A sorted table is filled in sorted order according to the defined table key, which must be unique. A sorted table can be accessed either by using the table index or the key, but the response time for key access is logarithmically proportional to the table size. A hashed table can only be accessed by using a unique key, which must be specified when declaring the table. A hashed table has no index, and the response time for key access is constant, regardless of the table size.
References: Internal Tables - ABAP Keyword Documentation, SAP ABAP: Types Of Internal Table Declaration - dan852.com

The ABAP SQL clause that allows the use of inline declarations is the INTO clause. The INTO clause is used to specify the target variable or field symbol where the result of the SQL query is stored. The INTO clause can use inline declarations to declare the target variable or field symbol at the same position where it is used, without using a separate DATA or FIELD-SYMBOLS statement. The inline declaration is performed using the DATA or @DATA operators in the declaration expression12. For example:
* The following code snippet uses the INTO clause with an inline declaration to declare a local variable itab and store the result of the SELECT query into it:
SELECT * FROM scarr INTO TABLE @DATA (itab).
* The following code snippet uses the INTO clause with an inline declaration to declare a field symbol
<fs> and store the result of the SELECT query into it:
SELECT SINGLE * FROM scarr INTO @<fs>.
You cannot do any of the following:
* FROM: The FROM clause is used to specify the data source of the SQL query, such as a table, a view, or a join expression. The FROM clause does not allow the use of inline declarations12.
* INTO CORRESPONDING FIELDS OF: The INTO CORRESPONDING FIELDS OF clause is used to specify the target structure or table where the result of the SQL query is stored. The INTO CORRESPONDING FIELDS OF clause does not allow the use of inline declarations. The target structure or table must be declared beforehand using a DATA or FIELD-SYMBOLS statement12.
* FIELDS: The FIELDS clause is used to specify the columns or expressions that are selected from the data source of the SQL query. The FIELDS clause does not allow the use of inline declarations. The FIELDS clause must be followed by an INTO clause that specifies the target variable or field symbol where the result is stored12.
References: 1: SELECT - ABAP Keyword Documentation - SAP Online Help 2: Inline Declarations - ABAP Keyword Documentation - SAP Online Help

A CDS view is a data definition that defines a data structure and a data selection from one or more data sources. A CDS view consists of several parts, but two of them are:
* Extension: An extension is an optional clause that allows a CDS view to extend another CDS view by adding new elements, annotations, or associations. The extension clause has the syntax EXTEND VIEW view_name WITH view_name. The first view_name is the name of the CDS view that is being extended, and the second view_name is the name of the CDS view that is doing the extension1.
* Field list: A field list is a mandatory clause that specifies the elements of the CDS view. The field list has the syntax SELECT FROM data_source { element_list }. The data_source is the name of the data
* source that the CDS view selects data from, and the element_list is a comma-separated list of elements that the CDS view exposes. The elements can be fields of the data source, expressions, associations, or annotations2.
The following example shows a CDS view that extends another CDS view and defines a field list:
@AbapCatalog.sqlViewName: 'ZCDS_EXT' define view Z_CDS_Extension extend view Z_CDS_Base with Z_CDS_Extension as select from ztable { // field list key ztable.id as ID, ztable.name as Name, ztable.age as Age, // extension @Semantics.currencyCode: true ztable.currency as Currency } The other options are not parts of a CDS view, but rather related concepts:
* Partitioning attributes: Partitioning attributes are attributes that are used to partition a table into smaller subsets of data. Partitioning attributes are defined in the ABAP Dictionary for transparent tables and can improve the performance and scalability of data access. Partitioning attributes are not part of the CDS view definition, but rather the underlying table definition3.
* Semantic table attributes: Semantic table attributes are attributes that provide additional information about the meaning and usage of a table. Semantic table attributes are defined in the ABAP Dictionary for transparent tables and can be used to enhance the data modeling and consumption of the table. Semantic table attributes are not part of the CDS view definition, but rather the underlying table definition4.
References: 1: Extending CDS Views | SAP Help Portal 2: SELECT List - ABAP Keyword Documentation 3:
Partitioning Attributes - ABAP Keyword Documentation 4: Semantic Table Attributes - ABAP Keyword Documentation

The following are the explanations for each ABAP SQL statement:
* A: This statement is valid. It selects the fields carrid, airpfrom, and the aggregate functions MAX(distance) and MIN(distance) from the table /dmo/connection, and groups the results by carrid and airpfrom. The aggregate functions are aliased as dist_max and dist_min. The results are stored in an internal table named It_hits, which is created using the inline declaration operator @DATA.
* B: This statement is valid. It is similar to statement A, except that it does not specify the GROUP BY clause. This means that the aggregate functions are applied to the entire table, and the results are stored in an internal table named It_hits, which is created using the inline declaration operator @DATA.
* C: This statement is invalid. It selects the aggregate functions MAX(distance) and MIN(distance) from the table /dmo/connection, but it does not specify any grouping or non-aggregate fields. This is not allowed in ABAP SQL, as the SELECT list must contain at least one non-aggregate field or a GROUP BY clause. The statement will cause a syntax error.
* D: This statement is invalid. It selects the fields carrid and airpfrom from the table /dmo/connection, and groups the results by carrid and connid. However, the field connid is not included in the SELECT list, which is not allowed in ABAP SQL, as the GROUP BY clause must contain only fields that are also in the SELECT list. The statement will cause a syntax error.
References: SELECT - ABAP Keyword Documentation, GROUP BY - ABAP Keyword Documentation