chore(cqn4sql): make it possible to use nice aliases again

[patricebender]

A while back we introduced technical aliases (like $B, $a, etc.) to prevent ambiguities for some OData requests.

However, sometimes it is nice to have readable aliases again, e.g., for presentations or debugging.

Set the environment variable USE_TECHNICAL_ALIAS=false to get nice aliases again:

USE_TECHNICAL_ALIAS=false cds r --run .
> cds.ql`SELECT author.name, genre.name from ${Books} where exists author[books.genre.name == 'Fantasy']`.toSQL().sql

--- nice.sql
+++ technical.sql
@@ -1,15 +1,15 @@
 SELECT author.name as author_name,
   genre.name as genre_name
-FROM sap_capire_bookshop_Books as Books
-  left JOIN sap_capire_bookshop_Authors as author ON author.ID = Books.author_ID
-  left JOIN sap_capire_bookshop_Genres as genre ON genre.ID = Books.genre_ID
+FROM sap_capire_bookshop_Books as "$B"
+  left JOIN sap_capire_bookshop_Authors as author ON author.ID = "$B".author_ID
+  left JOIN sap_capire_bookshop_Genres as genre ON genre.ID = "$B".genre_ID
 WHERE exists (
     SELECT 1 as "1"
-    FROM sap_capire_bookshop_Authors as author2
-      inner JOIN sap_capire_bookshop_Books as books2 ON books2.author_ID = author2.ID
+    FROM sap_capire_bookshop_Authors as "$a"
+      inner JOIN sap_capire_bookshop_Books as books ON books.author_ID = "$a".ID
       inner JOIN sap_capire_bookshop_Genres as genre2 ON genre2.ID = books.genre_ID
-    WHERE author2.ID = Books.author_ID
+    WHERE "$a".ID = "$B".author_ID
       and genre2.name is 'Fantasy'
   );

[Akatuoro]

This is really good for making the queries more readable 👍 It does not need to be used in production where there may be reasons for technical aliases, but especially for inspecting the SQL, it is quite helpful:

Maybe we could use CDS_USE_TECHNICAL_ALIAS as environmental variable (or some option in the cds env) to make sure that we don't clash with application defined ones (as unlikely as that is).