MDEV-7773: Aggregate stored functions

This commit implements aggregate stored functions. The basic idea behind
the feature is:

* Implement a special instruction FETCH GROUP NEXT ROW that will pause
the execution of the stored function. When the instruction is reached,
execution of the initial query resumes "as if" the function returned.
This gives the server the opportunity to advance to the next row in the
result set.

* Stored aggregates behave like regular aggregate functions. The
implementation of thus resides in the class Item_sum_sp. Because it is
an aggregate function, for each new row in the group, the
Item_sum_sp::add() method will be called. This is when execution resumes
and the function does another iteration to "add" one extra element to
the final result.

* When the end of group is reached, val_xxx() method will be called for
the item. This case is handled by another execute step for the stored
function, only with a special flag to force a call to the return
handler. See Item_sum_sp::execute() for details.

To allow this pause and resume semantic, we must preserve the function
context across executions. This is stored in Item_sp::sp_query_arena only for
aggregate stored functions, but has no impact for regular functions.

We also enforce aggregate functions to include the "FETCH GROUP NEXT ROW"
instruction.

Signed-off-by: Vicențiu Ciorbaru <vicentiu@mariadb.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mysql-test/t/sp-destruct.test b/mysql-test/t/sp-destruct.test
index 31da235d906..0cd80bd5427 100644
--- a/mysql-test/t/sp-destruct.test
+++ b/mysql-test/t/sp-destruct.test
@@ -10,7 +10,7 @@
 -- source include/not_embedded.inc
 
 # Supress warnings written to the log file
-call mtr.add_suppression("Column count of mysql.proc is wrong. Expected 20, found 19. The table is probably corrupted");
+call mtr.add_suppression("Column count of mysql.proc is wrong. Expected 21, found 20. The table is probably corrupted");
 call mtr.add_suppression("Stored routine .test...bug14233_[123].: invalid value in column mysql.proc");
 
 # Backup proc table