If you want to put HTTP methods in terms of SQL CRUD then think of it this way.

POST is like a INSERT on a table with a auto incrementing primary key, you insert the data into the table and the SQL server tells you what the data is identified as. When you POST to a web service, the web service tells you what the data is identified as.

   For SQL:

   INSERT INTO people (first, last) VALUES ("Eric", "Moritz");
   SELECT id FROM people WHERE first = "Eric" and last = "Moritz";

   For HTTP:

   > POST /people/
   > Content-Type: application/json
   > 
   > {"first": "Eric", "last": "Moritz"}

   < HTTP/1.1 201 Created
   < Content-Location: /people/1
   <
   < {"first": "Eric", "last": "Moritz"}
   

PUT can function like an UPDATE on a table using it's primary key. For instance:

   For SQL:

   UPDATE people set first = "Eric" where id = 1;

   For HTTP:

   > PUT /people/1/first
   > Content-Type: text/plain
   > 
   > Eric
   
   < HTTP/1.1 200 OK
   < Content-Type: application/json
   <
   < Eric

A PUT can also be used to create a resource:

   For SQL:

   INSERT INTO people (id, first, last) VALUES (1, "Eric", "Moritz");

   For HTTP:

   > PUT /people/1
   > Content-Type: application/json
   > 
   > {"first": "Eric", "last": "Moritz"}

   < HTTP/1.1 201 Created
   <
   < {"first": "Eric", "last": "Moritz"}

It's common to use POST for creation and PUT for updates. PUT, as GET, should be idempotent.