Fixed save/restore of current database when calling a procedure.

Docs/sp-imp-spec.txt

@@ -243,6 +243,23 @@
     5) On success, set the new values of the OUT and INOUT parameters in
        the caller's frame.
 
+    - USE database
+
+      Before executing the instruction we also keeps the current default
+      database (if any). If this was changed during execution (i.e. a "USE"
+      statement has been executed), we restore the current database to the
+      original.
+
+      This is the most useful way to handle USE in procedures. If we didn't,
+      the caller would find himself in a different database after calling
+      a function, which can be confusing.
+      Restoring the database also gives full freedom to the procedure writer:
+      - It's possible to write "general" procedures that are independent of
+        the actual database name.
+      - It's possible to write procedures that work on a particular database
+        by calling USE, without having to use fully qualified table names
+	everywhere (which doesn't help if you want to call other, "general",
+	procedures anyway).
 
     - Evaluating Items
 
@@ -340,6 +357,9 @@
     Dropping is done by simply getting the procedure with the sp_find()
     function and calling sp_drop() (both in sp.{cc,h}).
 
+    DROP PROCEDURE/FUNCTION also supports the non-standard "IF EXISTS",
+    analogous to other DROP statements in MySQL.
+
 
   - Class and function APIs
 

mysql-test/r/sp.result

@@ -18,6 +18,16 @@ id	data
 foo	42
 delete from t1;
 drop procedure foo42;
+create procedure u()
+use sptmp;
+create database sptmp;
+use test;
+call u();
+select database();
+database()
+test
+drop database sptmp;
+drop procedure u;
 create procedure bar(x char(16), y int)
 insert into test.t1 values (x, y);
 call bar("bar", 666);

mysql-test/t/sp.test

@@ -31,6 +31,18 @@ delete from t1;
 drop procedure foo42;
 
 
+# USE test: Make sure we remain in the same DB.
+create procedure u()
+  use sptmp;
+
+create database sptmp;
+use test;
+call u();
+select database();
+drop database sptmp;
+drop procedure u;
+
+
 # Single statement, two IN params.
 create procedure bar(x char(16), y int)
   insert into test.t1 values (x, y);

sql/sp_head.cc

@@ -131,9 +131,14 @@ int
 sp_head::execute(THD *thd)
 {
   DBUG_ENTER("sp_head::execute");
+  char *olddbname;
+  char *olddbptr= thd->db;
   int ret= 0;
   uint ip= 0;
 
+  if (olddbptr)
+    olddbname= my_strdup(olddbptr, MYF(MY_WME));
+
   do
   {
     sp_instr *i;
@@ -144,6 +149,16 @@ sp_head::execute(THD *thd)
     DBUG_PRINT("execute", ("Instruction %u", ip));
     ret= i->execute(thd, &ip);
   } while (ret == 0);
+
+  /* If the DB has changed, the pointer has changed too, but the
+     original thd->db will then have been freed */
+  if (olddbptr && olddbptr != thd->db && olddbname)
+  {
+    /* QQ Maybe we should issue some special error message or warning here,
+       if this fails?? */
+    ret= mysql_change_db(thd, olddbname);
+    my_free(olddbname, MYF(0));
+  }
   DBUG_RETURN(ret);
 }