doc: Simplify mention of unique indexes for NULL control

Discussion: https://postgr.es/m/2304.1586532634@sss.pgh.pa.us

Backpatch-through: 9.5

diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml
index 86539a781c5b9c8848c28526337e6b73658d39f1..56fd0a3d3d39de95017e05886eac2d2c2e18c7a3 100644 (file)
--- a/doc/src/sgml/indices.sgml
+++ b/doc/src/sgml/indices.sgml
@@ -705,15 +705,6 @@ CREATE INDEX test1_lower_col1_idx ON test1 (lower(col1));
 
   
 
-  
-   Expression indexes also allow control over the scope of unique indexes.
-   For example, this unique index prevents duplicate integer values from
-   being stored in a double precision-typed column:
-
-CREATE UNIQUE INDEX test1_uniq_int ON tests ((floor(double_col)))
-
-  
-
   
    If we were to declare this index UNIQUE, it would prevent
    creation of rows whose col1 values differ only in case,
@@ -953,18 +944,11 @@ CREATE UNIQUE INDEX tests_success_constraint ON tests (subject, target)
     WHERE success;
 
     This is a particularly efficient approach when there are few
-    successful tests and many unsuccessful ones.
+    successful tests and many unsuccessful ones.  It is also possible to
+    allow only one null in a column by creating a unique partial index
+    with an IS NULL restriction.
    
 
-   
-    This index allows only one null in the indexed column by using a
-    partial index clause to process only null column values, and using
-    an expression index clause to index true instead
-    of null:
-
-CREATE UNIQUE INDEX tests_target_one_null ON tests ((target IS NULL)) WHERE target IS NULL;
-
-