doc: document the CREATE INDEX "USING" clause

Somehow this was in the syntax but had no description.

Reported-by: [email protected]
Discussion: https://postgr.es/m/164228771825.31954.2719791849363756957@wrigleys.postgresql.org

Backpatch-through: 10

diff --git a/doc/src/sgml/ref/create_index.sgml b/doc/src/sgml/ref/create_index.sgml
index a5bac9f737368829e8b8b0dba986f61d59f88eac..944fdb4b094a984db897f3c0d7a8e56a826ecf2d 100644 (file)
--- a/doc/src/sgml/ref/create_index.sgml
+++ b/doc/src/sgml/ref/create_index.sgml
@@ -149,6 +149,18 @@ CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] 
       
      
 
+     
+      USING
+      
+       
+        The optional USING clause specifies an index
+        type as described in .  If not
+        specified, a default index type will be used based on the
+        data types of the columns.
+       
+      
+     
+
      
       INCLUDE