A fix and a test case for

 Bug#19022 "Memory bug when switching db during trigger execution"
 Bug#17199 "Problem when view calls function from another database."
 Bug#18444 "Fully qualified stored function names don't work correctly in
            SELECT statements"

 Documentation note: this patch introduces a change in behaviour of prepared
 statements.

 This patch adds a few new invariants with regard to how THD::db should
 be used. These invariants should be preserved in future:

  - one should never refer to THD::db by pointer and always make a deep copy
    (strmake, strdup)
  - one should never compare two databases by pointer, but use strncmp or
    my_strncasecmp
  - TABLE_LIST object table->db should be always initialized in the parser or
    by creator of the object.

    For prepared statements it means that if the current database is changed
    after a statement is prepared, the database that was current at prepare
    remains active. This also means that you can not prepare a statement that
    implicitly refers to the current database if the latter is not set.
    This is not documented, and therefore needs documentation. This is NOT a
    change in behavior for almost all SQL statements except:
     - ALTER TABLE t1 RENAME t2 
     - OPTIMIZE TABLE t1
     - ANALYZE TABLE t1
     - TRUNCATE TABLE t1 --
     until this patch t1 or t2 could be evaluated at the first execution of
     prepared statement. 

     CURRENT_DATABASE() still works OK and is evaluated at every execution
     of prepared statement.

     Note, that in stored routines this is not an issue as the default
     database is the database of the stored procedure and "use" statement
     is prohibited in stored routines.

  This patch makes obsolete the use of check_db_used (it was never used in the
  old code too) and all other places that check for table->db and assign it
  from THD::db if it's NULL, except the parser.

 How this patch was created: THD::{db,db_length} were replaced with a
 LEX_STRING, THD::db. All the places that refer to THD::{db,db_length} were
 manually checked and:
  - if the place uses thd->db by pointer, it was fixed to make a deep copy
  - if a place compared two db pointers, it was fixed to compare them by value
    (via strcmp/my_strcasecmp, whatever was approproate)
 Then this intermediate patch was used to write a smaller patch that does the
 same thing but without a rename.

 TODO in 5.1:
   - remove check_db_used
   - deploy THD::set_db in mysql_change_db

 See also comments to individual files.

6 files changed, 317 insertions, 2 deletions

diff --git a/mysql-test/r/create.result b/mysql-test/r/create.result
index 27a6c8a9d03..c5b77ea4925 100644
--- a/mysql-test/r/create.result
+++ b/mysql-test/r/create.result
@@ -607,7 +607,7 @@ create database mysqltest;
 use mysqltest;
 drop database mysqltest;
 create table test.t1 like x;
-ERROR 42000: Incorrect database name 'NULL'
+ERROR 3D000: No database selected
 drop table if exists test.t1;
 create database mysqltest;
 use mysqltest;
diff --git a/mysql-test/r/ps.result b/mysql-test/r/ps.result
index abebfc8cd93..3ce2f5169e2 100644
--- a/mysql-test/r/ps.result
+++ b/mysql-test/r/ps.result
@@ -1158,3 +1158,108 @@ Warnings:
 Error	1146	Table 'test.t4' doesn't exist
 deallocate prepare stmt;
 drop table t1, t2, t3;
+create database mysqltest_long_database_name_to_thrash_heap;
+use test;
+create table t1 (i int);
+prepare stmt from "alter table test.t1 rename t1";
+use mysqltest_long_database_name_to_thrash_heap;
+execute stmt;
+show tables like 't1';
+Tables_in_mysqltest_long_database_name_to_thrash_heap (t1)
+prepare stmt from "alter table test.t1 rename t1";
+use test;
+execute stmt;
+show tables like 't1';
+Tables_in_test (t1)
+use mysqltest_long_database_name_to_thrash_heap;
+show tables like 't1';
+Tables_in_mysqltest_long_database_name_to_thrash_heap (t1)
+t1
+deallocate prepare stmt;
+use mysqltest_long_database_name_to_thrash_heap;
+prepare stmt_create from "create table t1 (i int)";
+prepare stmt_insert from "insert into t1 (i) values (1)";
+prepare stmt_update from "update t1 set i=2";
+prepare stmt_delete from "delete from t1 where i=2";
+prepare stmt_select from "select * from t1";
+prepare stmt_alter from "alter table t1 add column (b int)";
+prepare stmt_alter1 from "alter table t1 drop column b";
+prepare stmt_analyze from "analyze table t1";
+prepare stmt_optimize from "optimize table t1";
+prepare stmt_show from "show tables like 't1'";
+prepare stmt_truncate from "truncate table t1";
+prepare stmt_drop from "drop table t1";
+drop table t1;
+use test;
+execute stmt_create;
+show tables like 't1';
+Tables_in_test (t1)
+use mysqltest_long_database_name_to_thrash_heap;
+show tables like 't1';
+Tables_in_mysqltest_long_database_name_to_thrash_heap (t1)
+t1
+use test;
+execute stmt_insert;
+select * from mysqltest_long_database_name_to_thrash_heap.t1;
+i
+1
+execute stmt_update;
+select * from mysqltest_long_database_name_to_thrash_heap.t1;
+i
+2
+execute stmt_delete;
+execute stmt_select;
+i
+execute stmt_alter;
+show columns from mysqltest_long_database_name_to_thrash_heap.t1;
+Field	Type	Null	Key	Default	Extra
+i	int(11)	YES		NULL	
+b	int(11)	YES		NULL	
+execute stmt_alter1;
+show columns from mysqltest_long_database_name_to_thrash_heap.t1;
+Field	Type	Null	Key	Default	Extra
+i	int(11)	YES		NULL	
+execute stmt_analyze;
+Table	Op	Msg_type	Msg_text
+mysqltest_long_database_name_to_thrash_heap.t1	analyze	status	Table is already up to date
+execute stmt_optimize;
+Table	Op	Msg_type	Msg_text
+mysqltest_long_database_name_to_thrash_heap.t1	optimize	status	Table is already up to date
+execute stmt_show;
+Tables_in_mysqltest_long_database_name_to_thrash_heap (t1)
+t1
+execute stmt_truncate;
+execute stmt_drop;
+show tables like 't1';
+Tables_in_test (t1)
+use mysqltest_long_database_name_to_thrash_heap;
+show tables like 't1';
+Tables_in_mysqltest_long_database_name_to_thrash_heap (t1)
+drop database mysqltest_long_database_name_to_thrash_heap;
+prepare stmt_create from "create table t1 (i int)";
+ERROR 3D000: No database selected
+prepare stmt_insert from "insert into t1 (i) values (1)";
+ERROR 3D000: No database selected
+prepare stmt_update from "update t1 set i=2";
+ERROR 3D000: No database selected
+prepare stmt_delete from "delete from t1 where i=2";
+ERROR 3D000: No database selected
+prepare stmt_select from "select * from t1";
+ERROR 3D000: No database selected
+prepare stmt_alter from "alter table t1 add column (b int)";
+ERROR 3D000: No database selected
+prepare stmt_alter1 from "alter table t1 drop column b";
+ERROR 3D000: No database selected
+prepare stmt_analyze from "analyze table t1";
+ERROR 3D000: No database selected
+prepare stmt_optimize from "optimize table t1";
+ERROR 3D000: No database selected
+prepare stmt_show from "show tables like 't1'";
+ERROR 3D000: No database selected
+prepare stmt_truncate from "truncate table t1";
+ERROR 3D000: No database selected
+prepare stmt_drop from "drop table t1";
+ERROR 3D000: No database selected
+create temporary table t1 (i int);
+ERROR 3D000: No database selected
+use test;
diff --git a/mysql-test/r/sp.result b/mysql-test/r/sp.result
index ff378f1f43b..a2b36b11a2e 100644
--- a/mysql-test/r/sp.result
+++ b/mysql-test/r/sp.result
@@ -4990,4 +4990,50 @@ CALL bug18037_p2()|
 DROP FUNCTION bug18037_f1|
 DROP PROCEDURE bug18037_p1|
 DROP PROCEDURE bug18037_p2|
+use test|
+create table t3 (i int)|
+insert into t3 values (1), (2)|
+create database mysqltest1|
+use mysqltest1|
+create function bug17199() returns varchar(2) deterministic return 'ok'|
+use test|
+select *, mysqltest1.bug17199() from t3|
+i	mysqltest1.bug17199()
+1	ok
+2	ok
+use mysqltest1|
+create function bug18444(i int) returns int no sql deterministic return i + 1|
+use test|
+select mysqltest1.bug18444(i) from t3|
+mysqltest1.bug18444(i)
+2
+3
+drop database mysqltest1|
+create database mysqltest1 charset=utf8|
+create database mysqltest2 charset=utf8|
+create procedure mysqltest1.p1()
+begin
+-- alters the default collation of database test 
+alter database character set koi8r;
+end|
+use mysqltest1|
+call p1()|
+show create database mysqltest1|
+Database	Create Database
+mysqltest1	CREATE DATABASE `mysqltest1` /*!40100 DEFAULT CHARACTER SET koi8r */
+show create database mysqltest2|
+Database	Create Database
+mysqltest2	CREATE DATABASE `mysqltest2` /*!40100 DEFAULT CHARACTER SET utf8 */
+alter database mysqltest1 character set utf8|
+use mysqltest2|
+call mysqltest1.p1()|
+show create database mysqltest1|
+Database	Create Database
+mysqltest1	CREATE DATABASE `mysqltest1` /*!40100 DEFAULT CHARACTER SET koi8r */
+show create database mysqltest2|
+Database	Create Database
+mysqltest2	CREATE DATABASE `mysqltest2` /*!40100 DEFAULT CHARACTER SET utf8 */
+drop database mysqltest1|
+drop database mysqltest2|
+use test|
 drop table t1,t2;
diff --git a/mysql-test/t/create.test b/mysql-test/t/create.test
index e22c2b5c426..07edbf206fe 100644
--- a/mysql-test/t/create.test
+++ b/mysql-test/t/create.test
@@ -517,7 +517,7 @@ DROP TABLE t12913;
 create database mysqltest;
 use mysqltest;
 drop database mysqltest;
---error 1102
+--error ER_NO_DB_ERROR 
 create table test.t1 like x;
 --disable_warnings
 drop table if exists test.t1;
diff --git a/mysql-test/t/ps.test b/mysql-test/t/ps.test
index e3f3e37cd4c..ff66b265fae 100644
--- a/mysql-test/t/ps.test
+++ b/mysql-test/t/ps.test
@@ -1146,4 +1146,122 @@ execute stmt;
 execute stmt;
 deallocate prepare stmt;
 drop table t1, t2, t3;
+
+#
+# Bug#17199 "Table not found" error occurs if the query contains a call
+#            to a function from another database.
+#            Test prepared statements- related behaviour.
+#
+#
+# ALTER TABLE RENAME and Prepared Statements: wrong DB name buffer was used
+# in ALTER ... RENAME which caused memory corruption in prepared statements.
+# No need to fix this problem in 4.1 as ALTER TABLE is not allowed in
+# Prepared Statements in 4.1.
+#
+create database mysqltest_long_database_name_to_thrash_heap;
+use test;
+create table t1 (i int);
+prepare stmt from "alter table test.t1 rename t1";
+use mysqltest_long_database_name_to_thrash_heap;
+execute stmt;
+show tables like 't1';
+prepare stmt from "alter table test.t1 rename t1";
+use test;
+execute stmt;
+show tables like 't1';
+use mysqltest_long_database_name_to_thrash_heap;
+show tables like 't1';
+deallocate prepare stmt;
+#
+# Check that a prepared statement initializes its current database at
+# PREPARE, and then works correctly even if the current database has been
+# changed.
+# 
+use mysqltest_long_database_name_to_thrash_heap; 
+# Necessary for preparation of INSERT/UPDATE/DELETE to succeed
+prepare stmt_create from "create table t1 (i int)";
+prepare stmt_insert from "insert into t1 (i) values (1)";
+prepare stmt_update from "update t1 set i=2";
+prepare stmt_delete from "delete from t1 where i=2";
+prepare stmt_select from "select * from t1";
+prepare stmt_alter from "alter table t1 add column (b int)";
+prepare stmt_alter1 from "alter table t1 drop column b";
+prepare stmt_analyze from "analyze table t1";
+prepare stmt_optimize from "optimize table t1";
+prepare stmt_show from "show tables like 't1'";
+prepare stmt_truncate from "truncate table t1";
+prepare stmt_drop from "drop table t1";
+# Drop the table that was used to prepare INSERT/UPDATE/DELETE: we will
+# create a new one by executing stmt_create
+drop table t1;
+# Switch the current database
+use test;
+# Check that all prepared statements operate on the database that was
+# active at PREPARE
+execute stmt_create;
+# should return empty set
+show tables like 't1';
+use mysqltest_long_database_name_to_thrash_heap;
+show tables like 't1';
+use test;
+execute stmt_insert;
+select * from mysqltest_long_database_name_to_thrash_heap.t1;
+execute stmt_update;
+select * from mysqltest_long_database_name_to_thrash_heap.t1;
+execute stmt_delete;
+execute stmt_select;
+execute stmt_alter;
+show columns from mysqltest_long_database_name_to_thrash_heap.t1;
+execute stmt_alter1;
+show columns from mysqltest_long_database_name_to_thrash_heap.t1;
+execute stmt_analyze;
+execute stmt_optimize;
+execute stmt_show;
+execute stmt_truncate;
+execute stmt_drop;
+show tables like 't1';
+use mysqltest_long_database_name_to_thrash_heap;
+show tables like 't1';
+#
+# Attempt a statement PREPARE when there is no current database:
+# is expected to return an error.
+#
+drop database mysqltest_long_database_name_to_thrash_heap;
+--error ER_NO_DB_ERROR
+prepare stmt_create from "create table t1 (i int)";
+--error ER_NO_DB_ERROR
+prepare stmt_insert from "insert into t1 (i) values (1)";
+--error ER_NO_DB_ERROR
+prepare stmt_update from "update t1 set i=2";
+--error ER_NO_DB_ERROR
+prepare stmt_delete from "delete from t1 where i=2";
+--error ER_NO_DB_ERROR
+prepare stmt_select from "select * from t1";
+--error ER_NO_DB_ERROR
+prepare stmt_alter from "alter table t1 add column (b int)";
+--error ER_NO_DB_ERROR
+prepare stmt_alter1 from "alter table t1 drop column b";
+--error ER_NO_DB_ERROR
+prepare stmt_analyze from "analyze table t1";
+--error ER_NO_DB_ERROR
+prepare stmt_optimize from "optimize table t1";
+--error ER_NO_DB_ERROR
+prepare stmt_show from "show tables like 't1'";
+--error ER_NO_DB_ERROR
+prepare stmt_truncate from "truncate table t1";
+--error ER_NO_DB_ERROR
+prepare stmt_drop from "drop table t1";
+#
+# The above has automatically deallocated all our statements.
+#
+# Attempt to CREATE a temporary table when no DB used: it should fail
+# This proves that no table can be used without explicit specification of
+# its database if there is no current database. 
+#
+--error ER_NO_DB_ERROR
+create temporary table t1 (i int);
+#
+# Restore the old environemnt
+#
+use test;
 # End of 5.0 tests
diff --git a/mysql-test/t/sp.test b/mysql-test/t/sp.test
index 1d21a5da187..c0dd785a8ce 100644
--- a/mysql-test/t/sp.test
+++ b/mysql-test/t/sp.test
@@ -5888,6 +5888,52 @@ DROP FUNCTION bug18037_f1|
 DROP PROCEDURE bug18037_p1|
 DROP PROCEDURE bug18037_p2|
 
+#
+# Bug#17199: "Table not found" error occurs if the query contains a call
+#            to a function from another database.
+#            See also ps.test for an additional test case for this bug.
+#
+use test|
+create table t3 (i int)|
+insert into t3 values (1), (2)|
+create database mysqltest1|
+use mysqltest1|
+create function bug17199() returns varchar(2) deterministic return 'ok'|
+use test|
+select *, mysqltest1.bug17199() from t3|
+#
+# Bug#18444: Fully qualified stored function names don't work correctly
+#            in select statements
+#
+use mysqltest1|
+create function bug18444(i int) returns int no sql deterministic return i + 1|
+use test|
+select mysqltest1.bug18444(i) from t3|
+drop database mysqltest1|
+#
+# Check that current database has no influence to a stored procedure
+#
+create database mysqltest1 charset=utf8|
+create database mysqltest2 charset=utf8|
+create procedure mysqltest1.p1()
+begin
+-- alters the default collation of database test 
+  alter database character set koi8r;
+end|
+use mysqltest1|
+call p1()|
+show create database mysqltest1|
+show create database mysqltest2|
+alter database mysqltest1 character set utf8|
+use mysqltest2|
+call mysqltest1.p1()|
+show create database mysqltest1|
+show create database mysqltest2|
+drop database mysqltest1|
+drop database mysqltest2|
+#
+# Restore the old environemnt
+use test|
 
 #
 # BUG#NNNN: New bug synopsis