Update MP SELECT Descendants.md

Author: pchemguy

MP SELECT Descendants.md

@@ -8,11 +8,11 @@ permalink: /mat-paths/select-desc
 
 ### Scope of provided selection queries for the MPs model
 
-This and the following sections provide a family of standard MPs queries for selecting a set of category tree nodes, their descendants, and ancestors. These queries return rows from the *categories* table for the following standard MPs node sets:
+Current and the following sections provide a family of standard MPs queries for selecting a set of category tree nodes, their descendants, and ancestors. These queries return rows from the *categories* table for the following standard MPs node sets:
 
   - root nodes (just the nodes from the input)
-  - all descendants, excluding the root nodes
   - subtrees, including root nodes and descendants
+  - all descendants, excluding the root nodes
   - children, i.e., direct descendants only
 
 All provided selection queries have the [modular CTEs-based](../meta/db-derived-cte) structure and take a unified input in the form of a [JSON-array-formatted](../patterns/json-sql-input) string
@@ -25,7 +25,7 @@ with a list of category *path* values, identifying subtree root nodes.
 
 ### Query structure and alternative category identifiers
 
-Each query starts with a prologue. Its function is to take the unified JSON array string of category identifiers (the *json_nodes* entry block) and its exit *tops* block produces a table containing the *path* column with one category path per row:
+Each query starts with a prologue. Its function is to take a unified JSON array string with category identifiers (the *json_nodes* entry block), and its exit *tops* block produces a table containing the *path* column with one category path per row:
 
 #### Prologue input
 
@@ -58,15 +58,15 @@ SELECT * FROM tops ORDER BY path;
 
 ---
 
-Query prologue decouples the input format details from the query business logic. With query prologue and its output format defined, the input format and query business logic can be modified indepently. For example, switching from path-based to ascii_id-based identifies requires a localized change to a single block *tops*, identical for all queries in this family (immediate input in *json_nodes* is also adjusted; in production, a query parameter replaces this string input):
+The query prologue decouples the input format details from the query business logic, permitting their independent modification. For example, switching from path-based to ascii_id-based identifies requires a localized change to a single block *tops*, identical for all queries in this family (immediate input in *json_nodes* is also adjusted; in production, a query parameter replaces this string input):
 
-#### Input
+#### Input - *ascii_id*
 
 ~~~json
 ["0FDAF2C8","65887f45"]
 ~~~
 
-#### Prologue
+#### Prologue - *ascii_id*
 
 ~~~sql
 WITH
@@ -78,19 +78,40 @@ WITH
         SELECT node_ids.value AS node_id
         FROM json_nodes AS jn, json_each(jn.ids) AS node_ids
     ),
-    tops AS (
-        SELECT cats.path
-        FROM categories AS cats, nodes
-        WHERE cats.ascii_id IN (nodes.node_id)
-    )
+    tops AS (SELECT path FROM categories WHERE ascii_id IN nodes)
 SELECT * FROM tops ORDER BY path;
 ~~~
 
 ---
 
-### MPs queries
+### Selection queries
+
+The following query selects just the nodes from the input (root nodes).
+
+~~~sql
+WITH
+    json_nodes(ids) AS (
+        VALUES
+            ('["tcl/compat/zlib1/", "BAZ/dev/git4win/x32/mingw32/share/"]')
+    ), 
+    nodes AS (
+        SELECT node_ids.value AS node_id
+        FROM json_nodes AS jn, json_each(jn.ids) AS node_ids
+    ),
+    tops AS (SELECT node_id AS path FROM nodes),
+    records AS (SELECT * FROM categories WHERE path IN nodes)
+SELECT * FROM records ORDER BY path;
+~~~
+
+The remaining three queries in this section have almost identical code, with the only difference in the WHERE clause (*records*). In the query template below, replace %SELECTOR% according to the following table:
 
-Note that the four queries have alomst identical code, with the only difference in the WHERE clause (*records*). Here is a query template:
+<pre>
+|  <b>node set</b>   |             <b>%SELECTOR%</b>            |
+|-------------|-----------------------------------|
+| subtrees    | cats.path   like tops.path || '%' |
+| descendants | cats.prefix like tops.path || '%' |
+| children    | cats.prefix  =   tops.path        |
+</pre>
 
 ~~~sql
 WITH
@@ -110,14 +131,3 @@ WITH
     )
 SELECT * FROM records ORDER BY path;
 ~~~
-
-in which %SELECTOR% should be replaced according to the following table
-
-<pre>
-|  <b>node set</b>   |              <b>%SELECTOR%</b>            |
-|-------------|------------------------------------|
-| root nodes  | cats.path    IN  (tops.path)       |
-| descendants | cats.prefix like  tops.path || '%' |
-| subtrees    | cats.path   like  tops.path || '%' |
-| children    | cats.prefix  =    tops.path        |
-</pre>