Update

03_ABAP_SQL.md

@@ -20,6 +20,7 @@
         - [Aggregate Expressions](#aggregate-expressions)
         - [Arithmetic, Cast, String Expressions, and Case Distinctions](#arithmetic-cast-string-expressions-and-case-distinctions)
         - [Window Expressions](#window-expressions)
+        - [coalesce Function](#coalesce-function)
     - [SQL Conditions](#sql-conditions)
     - [Selecting Data by Evaluating the Content of Other Tables](#selecting-data-by-evaluating-the-content-of-other-tables)
     - [Combining Data of Multiple Database Tables](#combining-data-of-multiple-database-tables)
@@ -626,7 +627,7 @@ SELECT FROM zdemo_abap_flsch
     on SQL expressions
     [here](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abapsql_expr.htm)
     and the subtopics there.
-- Built-in functions are available in ABAP SQL. The result is a value with the associated dictionary type. The arguments of the functions can cover one or more SQL expressions. Find more information [here](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenabap_sql_builtin_functions.htm).
+- Built-in SQL functions can be specified as standalone functions in ABAP SQL or as operands of SQL expressions. The result is a value with the associated dictionary type. The arguments of the functions can cover one or more SQL expressions. Find more information [here](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abenabap_sql_builtin_functions.htm).
 
 ##### Elementary Expressions
 
@@ -1078,6 +1079,60 @@ SELECT carrid, currency, fldate,
 
 <p align="right"><a href="#top">⬆️ back to top</a></p>
 
+##### coalesce Function
+
+Find more information [here](https://help.sap.com/doc/abapdocu_cp_index_htm/CLOUD/en-US/index.htm?file=abensql_coalesce.htm).
+
+
+```abap
+"The null value is a special value that is returned by a database. It indicates an
+"undefined value or result. Note that, in ABAP, there are no special null values. Do
+"not confuse the null value with a type-dependent initial value. When using SELECT
+"statements to read data, null values can be produced by, for example, outer joins.
+"When the null values are passed to a data object, they are transformed to the
+"type-dependent initial values. For more information, refer to the ABAP Keyword Documentation.
+"The following example uses a left outer join to intentionally create null values. For
+"this purpose, two demo database tables of the ABAP cheat sheet repository are cleared and
+"populated with specific values to visualize null values.
+DELETE FROM zdemo_abap_tab1.
+DELETE FROM zdemo_abap_tab2.
+MODIFY zdemo_abap_tab1 FROM TABLE @( VALUE #( ( key_field = 1 char1 = 'a' char2 = 'y' )
+                                              ( key_field = 2 char1 = 'b' char2 = 'z' ) ) ).
+MODIFY zdemo_abap_tab2 FROM TABLE @( VALUE #( ( key_field = 1 char1 = 'a' )
+                                              ( key_field = 2 char1 = 'a' )
+                                              ( key_field = 3 char1 = 'b' )
+                                              ( key_field = 4 ) ) ).
+
+"Note that for the entry 'key_field = 4' no char1 value was passed.
+"char1 is a shared column of the two database tables, and which is used in
+"the ON condition of the join. Since there is no entry in char1 for 'key_field = 4',
+"the joined values are null in that case.
+"The coalesce function is used to replace null values produced by an outer join with
+"a different value.
+SELECT tab2~key_field,
+       coalesce( tab1~char1, '-' ) AS coalesced1,
+       coalesce( tab1~char2, '#' ) AS coalesced2,
+       "A coalesce function is a short form of a complex
+       "case distinction such as the following:
+       CASE WHEN tab1~char1 IS NOT NULL THEN tab1~char1
+        ELSE '?'
+       END as coalesced3
+
+    FROM zdemo_abap_tab2 AS tab2
+    LEFT OUTER JOIN zdemo_abap_tab1 AS tab1 ON tab1~char1 = tab2~char1
+    INTO TABLE @DATA(join_w_null).
+
+*Example table content
+*KEY_FIELD    COALESCED1    COALESCED2    COALESCED3
+*1            a             y             a
+*2            a             y             a
+*3            b             z             b
+*4            -             #             ?
+```
+
+<p align="right"><a href="#top">⬆️ back to top</a></p>
+
+
 ### SQL Conditions
 
 You can formulate conditions in ABAP SQL statements, i. e. [logical