CTEs modifying the same table more than once - Mailing list pgsql-docs

In PostgreSQL 9.5, given a simple table created with:

create table tbl (   id serial primary key,   val integer
);

I run SQL to INSERT a value, then UPDATE it in the same statement:

WITH newval AS (   INSERT INTO tbl(val) VALUES (1) RETURNING id
) UPDATE tbl SET val=2 FROM newval WHERE tbl.id=newval.id;

The result is that the UPDATE is ignored:

testdb=> select * from tbl;
┌────┬─────┐
│ id │ val │
├────┼─────┤
│  1 │   1 │
└────┴─────┘
(1 row)