docs: add example to Selection Type = Sql Query

- show query example for `Selection Pattern` when `Selection Type` is Sql Query.

Signed-off-by: Bruno Friedmann <bruno.friedmann@bareos.com>
Co-authored-by: Jörg Steffens <joergsteffens@users.noreply.github.com>

docs/manuals/source/include/config/DirSelectionPatterns-sql1.conf

@@ -0,0 +1,19 @@
+
+# SQL selecting all jobid in pool "Full"
+# which is a terminated backup (T,W)
+# and was never copied or migrated (PriorJobid 0).
+
+Job {
+    Name = "<name>"
+    JobDefs = "DefaultJob"
+    Type = Migrate
+    Selection Type = SQL Query
+    # Multiple lines instructions is available since version 21.0.0
+    Selection Pattern = "WITH pids AS
+            ( SELECT poolid FROM pool WHERE name = 'Full' )
+            SELECT jobid FROM job j, pids p
+            WHERE j.poolid=p.poolid
+            AND type='B'
+            AND jobstatus IN ('T','W')
+            AND priorjobid = 0;"
+}

docs/manuals/source/manually_added_config_directive_descriptions/dir-job-SelectionPattern.rst.inc

@@ -5,3 +5,9 @@ For the OldestVolume and SmallestVolume, this Selection pattern is not used (ign
 For the Client, Volume, and Job keywords, this pattern must be a valid regular expression that will filter the appropriate item names found in the Pool.
 
 For the SQLQuery keyword, this pattern must be a valid :command:`SELECT` SQL statement that returns JobIds.
+
+Example:
+
+.. literalinclude:: /include/config/DirSelectionPatterns-sql1.conf
+   :language: bareosconfig
+