ob-sql: Option to reference connections in `sql-connection-alist'

* lisp/ob-sql.el (org-babel-find-db-connection-param): New function.

Provide a new param called :dbconnection, that can be used to
reference connections defined in `sql-connection-alist', a custom
variable defined in sql.el.

TINYCHANGE

lisp/ob-sql.el

@@ -39,6 +39,7 @@
 ;; - dbport
 ;; - dbuser
 ;; - dbpassword
+;; - dbconnection (to reference connections in sql-connection-alist)
 ;; - database
 ;; - colnames (default, nil, means "yes")
 ;; - result-params
@@ -174,16 +175,35 @@ Otherwise, use Emacs' standard conversion function."
 	((string= "windows-nt" system-type) file)
 	(t (format "%S" (convert-standard-filename file)))))
 
+(defun org-babel-find-db-connection-param (params name)
+  "Return database connection parameter NAME.
+Given a parameter NAME, if :dbconnection is defined in PARAMS
+then look for the parameter into the corresponding connection
+defined in `sql-connection-alist`, otherwise look into PARAMS.
+Look `sql-connection-alist` (part of SQL mode) for how to define
+database connections."
+  (if (assq :dbconnection params)
+      (let* ((dbconnection (cdr (assq :dbconnection params)))
+             (name-mapping '((:dbhost . sql-server)
+                             (:dbport . sql-port)
+                             (:dbuser . sql-user)
+                             (:dbpassword . sql-password)
+                             (:database . sql-database)))
+             (mapped-name (cdr (assq name name-mapping))))
+        (cadr (assq mapped-name
+                    (cdr (assoc dbconnection sql-connection-alist)))))
+    (cdr (assq name params))))
+
 (defun org-babel-execute:sql (body params)
   "Execute a block of Sql code with Babel.
 This function is called by `org-babel-execute-src-block'."
   (let* ((result-params (cdr (assq :result-params params)))
          (cmdline (cdr (assq :cmdline params)))
-         (dbhost (cdr (assq :dbhost params)))
-         (dbport (cdr (assq :dbport params)))
-         (dbuser (cdr (assq :dbuser params)))
-         (dbpassword (cdr (assq :dbpassword params)))
-         (database (cdr (assq :database params)))
+         (dbhost (org-babel-find-db-connection-param params :dbhost))
+         (dbport (org-babel-find-db-connection-param params :dbport))
+         (dbuser (org-babel-find-db-connection-param params :dbuser))
+         (dbpassword (org-babel-find-db-connection-param params :dbpassword))
+         (database (org-babel-find-db-connection-param params :database))
          (engine (cdr (assq :engine params)))
          (colnames-p (not (equal "no" (cdr (assq :colnames params)))))
          (in-file (org-babel-temp-file "sql-in-"))