Generalize index support to handle constraints, fix #251.

PostgreSQL rightfully forbifs DROP INDEX when the index is used to
enforce a constraint, the proper SQL to issue is then ALTER TABLE DROP
CONSTRAINT. Also, in such a case pg_dump issues a single ALTER TABLE ADD
CONSTRAINT statement to restore the situation.

Have pgloader do the same with indexes that are used to back a constraint.

src/pgsql/queries.lisp

@@ -192,15 +192,18 @@
 (defun list-indexes (table-name)
   "List all indexes for TABLE-NAME in SCHEMA. A PostgreSQL connection must
    be already established when calling that function."
-  (loop :for (index-name table-name table-oid primary sql)
+  (loop :for (index-name table-name table-oid primary sql conname condef)
      :in (pomo:query (format nil "
 select i.relname,
        indrelid::regclass,
        indrelid,
        indisprimary,
-       pg_get_indexdef(indexrelid)
+       pg_get_indexdef(indexrelid),
+       c.conname,
+       pg_get_constraintdef(c.oid)
   from pg_index x
        join pg_class i ON i.oid = x.indexrelid
+       left join pg_constraint c ON c.conindid = i.oid
  where indrelid = '~@[~a.~]~a'::regclass"
                              (when (typep table-name 'cons)
                                (car table-name))
@@ -212,7 +215,9 @@ select i.relname,
                                 :table-oid table-oid
                                 :primary primary
                                 :columns nil
-                                :sql sql)))
+                                :sql sql
+                                :conname conname
+                                :condef condef)))
 
 (defun list-reserved-keywords (pgconn)
   "Connect to PostgreSQL DBNAME and fetch reserved keywords."

src/pgsql/schema.lisp

@@ -263,7 +263,11 @@
 ;;;
 ;;; Index support
 ;;;
-(defstruct pgsql-index name table-name table-oid primary unique columns sql)
+(defstruct pgsql-index
+  ;; the struct is used both for supporting new index creation from non
+  ;; PostgreSQL system and for drop/create indexes when using the 'drop
+  ;; indexes' option (in CSV mode and the like)
+  name table-name table-oid primary unique columns sql conname condef)
 
 (defgeneric index-table-name (index)
   (:documentation
@@ -289,6 +293,10 @@
 
 	 (cols (mapcar #'apply-identifier-case (pgsql-index-columns index))))
     (cond
+      ((pgsql-index-condef index)
+       (format nil "ALTER TABLE ~a ADD ~a;"
+               table-name (pgsql-index-condef index)))
+
       ((pgsql-index-primary index)
        (values
         ;; ensure good concurrency here, don't take the ACCESS EXCLUSIVE
@@ -312,9 +320,9 @@
   "Generate the PostgreSQL statement to DROP the index."
   (let* ((table-name (apply-identifier-case (pgsql-index-table-name index)))
 	 (index-name (apply-identifier-case (pgsql-index-name index))))
-    (cond ((pgsql-index-primary index)
+    (cond ((pgsql-index-conname index)
            (format nil "ALTER TABLE ~a DROP CONSTRAINT ~a;"
-                   table-name index-name))
+                   table-name (pgsql-index-conname index)))
 
           (t
            (format nil "DROP INDEX ~a;" index-name)))))