Bug#29223 declare cursor c for SHOW .....

"DECLARE CURSOR FOR SHOW ..." is a syntax that currently appears to work,
but is untested for some SHOW commands and does not work for other SHOW
commands.

Since this is an un-intended feature that leaked as a result of a coding bug
(in the parser grammar), the correct fix is to fix the grammar to not accept
this construct.

In other words, "DECLARE CURSOR FOR SHOW <other commands that don't work>"
is not considered a bug, and we will not implement other features to make all
the SHOW commands usable inside a cursor just because someone exploited a bug.


mysql-test/r/sp-error.result:
  Only allow declaring cursors for SELECT statements to avoid
  possible further confusion/problems.
mysql-test/t/information_schema.test:
  Only SELECT statements are allowed in cursors.
mysql-test/t/sp-error.test:
  Add test case for Bug#29223. Non-SELECT statements in cursors now
  yields a parser error.
sql/sql_yacc.yy:
  Rework DECLARE CURSOR statement to not allow non-SELECT statements.

mysql-test/t/sp-error.test

@@ -196,7 +196,7 @@ select f(10)|
 
 drop function f|
 
---error 1322
+--error ER_PARSE_ERROR
 create procedure p()
 begin
   declare c cursor for insert into test.t1 values ("foo", 42);
@@ -2178,6 +2178,27 @@ END//
 delimiter ;//
 
 
+#
+# Bug#29223 declare cursor c for SHOW .....
+#
+
+--disable_warnings
+DROP PROCEDURE IF EXISTS p1;
+--enable_warnings
+--delimiter |
+--error ER_PARSE_ERROR
+CREATE PROCEDURE p1()
+BEGIN
+  DECLARE c char(100);
+  DECLARE cur1 CURSOR FOR SHOW TABLES;
+
+  OPEN cur1;
+  FETCH cur1 INTO c;
+  select c;
+  CLOSE cur1;
+END|
+--delimiter ;
+
 #
 # BUG#NNNN: New bug synopsis
 #