Create MP DELETE Subtrees.md

Author: pchemguy

MP DELETE Subtrees.md

@@ -0,0 +1,32 @@
+---
+layout: default
+title: DELETE Subtrees
+nav_order: 7
+parent: Materialized Paths
+permalink: /mat-paths/delete
+---
+
+The following query performs a simple deletion via the database DELETE statement and associated cascades. This query contains a [modify-style prologue](modify#prologue), and the *targets* block prepares a list of deleted record IDs (the DELETE statement, as opposed to UPDATE, does not support joins).
+
+~~~sql
+WITH
+    json_ops(ops) AS (
+        VALUES
+            (json(
+                '['                                                                    ||
+                    '{"op":"delete", "path_old":"tcl/compat/zlib1/"},'                 ||
+                    '{"op":"delete", "path_old":"BAZ/dev/git4win/x32/mingw32/share/"}' ||
+                ']'
+            ))
+    ),
+    base_ops AS (
+        SELECT
+            "key" + 1 AS opid,
+            json_extract(value, '$.op') AS op,
+            json_extract(value, '$.path_old') AS path_old,
+            json_extract(value, '$.path_new') AS path_new
+        FROM json_ops AS jo, json_each(jo.ops) AS terms
+    ),
+    targets AS (SELECT path FROM categories, base_ops WHERE path like path_old || '%')
+DELETE FROM categories WHERE path IN targets;
+~~~