MDEV-27510 Query returns wrong result when using split optimization

This bug may affect the queries that uses a grouping derived table with
grouping list containing references to columns from different tables if
the optimizer decides to employ the split optimization for the derived
table. In some very specific cases it may affect queries with a grouping
derived table that refers only one base table.
This bug was caused by an improper fix for the bug MDEV-25128. The fix
tried to get rid of the equality conditions pushed into the where clause
of the grouping derived table T to which the split optimization had been
applied. The fix erroneously assumed that only those pushed equalities
that were used for ref access of the tables referenced by T were needed.
In fact the function remove_const() that figures out what columns from the
group list can be removed if the split optimization is applied can uses
other pushed equalities as well.
This patch actually provides a proper fix for MDEV-25128. Rather than
trying to remove invalid pushed equalities referencing the fields of SJM
tables with a look-up access the patch attempts not to push such equalities.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

1 files changed, 142 insertions, 0 deletions

diff --git a/mysql-test/main/derived_cond_pushdown.test b/mysql-test/main/derived_cond_pushdown.test
index 4f4ffc9e6d4..619d104951d 100644
--- a/mysql-test/main/derived_cond_pushdown.test
+++ b/mysql-test/main/derived_cond_pushdown.test
@@ -3711,4 +3711,146 @@ set  optimizer_switch='split_materialized=default';
 
 DROP TABLE t1,t2,t3;
 
+--echo #
+--echo # MDEV-27510: Splittable derived with grouping over two tables
+--echo #
+
+CREATE TABLE ledgers (
+  id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  name VARCHAR(32)
+) ENGINE=MyISAM;
+
+CREATE TABLE charges (
+  id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  from_ledger_id BIGINT UNSIGNED NOT NULL,
+  to_ledger_id BIGINT UNSIGNED NOT NULL,
+  amount INT NOT NULL,
+  KEY fk_charge_from_ledger (from_ledger_id),
+  KEY fk_charge_to_ledger (to_ledger_id)
+) ENGINE=MyISAM;
+
+CREATE TABLE transactions (
+  id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  ledger_id BIGINT UNSIGNED NOT NULL,
+  KEY fk_transactions_ledger (ledger_id)
+) ENGINE=MyISAM;
+
+CREATE TABLE transaction_items (
+  id BIGINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  transaction_id BIGINT UNSIGNED NOT NULL,
+  charge_id BIGINT UNSIGNED,
+  amount INT NOT NULL,
+  KEY fk_items_transaction (transaction_id),
+  KEY fk_items_charge (charge_id)
+) ENGINE=MyISAM;
+
+INSERT INTO ledgers (id, name) VALUES
+(1, 'Anna'), (2, 'John'), (3, 'Fred');
+
+INSERT INTO charges (id, from_ledger_id, to_ledger_id, amount) VALUES
+(1, 2, 1, 200), (2, 1, 2, 330), (3, 1, 2, 640), (4, 3, 1, 640), (5, 3, 2, 1000),
+(6, 3, 1, 660), (7, 2, 3, 650), (8, 3, 2, 160), (9, 2, 1, 740), (10, 3, 2, 310),
+(11, 2, 1, 640), (12, 3, 2, 240), (13, 3, 2, 340), (14, 2, 1, 720),
+(15, 2, 3, 100),
+(16, 2, 3, 980), (17, 2, 1, 80), (18, 1, 2, 760), (19, 2, 3, 740),
+(20, 2, 1, 990);
+
+INSERT INTO transactions (id, ledger_id) VALUES
+(2, 1), (3, 1), (5, 1), (8, 1), (12, 1), (18, 1), (22, 1), (28, 1),
+(34, 1), (35, 1),
+(40, 1), (1, 2), (4, 2), (6, 2), (10, 2), (13, 2), (16, 2), (17, 2),
+(20, 2), (21, 2),
+(24, 2), (26, 2), (27, 2), (29, 2), (31, 2), (33, 2), (36, 2), (37, 2),
+(39, 2), (7, 3),
+(9, 3), (11, 3), (14, 3), (15, 3), (19, 3), (23, 3), (25, 3), (30, 3),
+(32, 3), (38, 3);
+
+INSERT INTO transaction_items (id, transaction_id, charge_id, amount) VALUES
+(1, 1, 1, -200), (2, 2, 1, 200), (3, 3, 2, -330), (4, 4, 2, 330),
+(5, 5, 3, -640),
+(6, 6, 3, 640), (7, 7, 4, -640), (8, 8, 4, 640), (9, 9, 5, -1000),
+(10, 10, 5, 1000),
+(11, 11, 6, -660), (12, 12, 6, 660), (13, 13, 7, -650), (14, 14, 7, 650),
+(15, 15, 8, -160),
+(16, 16, 8, 160), (17, 17, 9, -740), (18, 18, 9, 740), (19, 19, 10, -310),
+(20, 20, 10, 310),
+(21, 21, 11, -640), (22, 22, 11, 640), (23, 23, 12, -240), (24, 24, 12, 240),
+(25, 25, 13, -340),
+(26, 26, 13, 340), (27, 27, 14, -720), (28, 28, 14, 720), (29, 29, 15, -100),
+(30, 30, 15, 100),
+(31, 31, 16, -980), (32, 32, 16, 980), (33, 33, 17, -80), (34, 34, 17, 80),
+(35, 35, 18, -760),
+(36, 36, 18, 760), (37, 37, 19, -740), (38, 38, 19, 740), (39, 39, 20, -990),
+(40, 40, 20, 990);
+
+ANALYZE TABLE ledgers, charges, transactions, transaction_items;
+
+let $q=
+SELECT
+    charges.id,
+    charges.from_ledger_id,
+    charges.to_ledger_id,
+    from_agg_items.num_rows AS from_num_rows
+FROM charges
+INNER JOIN (
+    SELECT
+        transactions.ledger_id,
+        transaction_items.charge_id,
+        count(*) as num_rows
+    FROM transaction_items
+    INNER JOIN transactions ON transaction_items.transaction_id = transactions.id
+    GROUP BY transactions.ledger_id, transaction_items.charge_id
+) AS from_agg_items
+ON from_agg_items.charge_id = charges.id AND
+   from_agg_items.ledger_id = charges.from_ledger_id
+WHERE charges.to_ledger_id = 2;
+
+set optimizer_switch='split_materialized=on';
+eval $q;
+eval EXPLAIN $q;
+eval EXPLAIN FORMAT=JSON $q;
+
+set optimizer_switch='split_materialized=off';
+eval $q;
+eval EXPLAIN $q;
+
+INSERT INTO charges (id, from_ledger_id, to_ledger_id, amount) VALUES
+(101, 4, 2, 100), (102, 7, 2, 200);
+
+let $q1=
+SELECT
+    charges.id,
+    charges.from_ledger_id,
+    charges.to_ledger_id,
+    from_agg_items.num_rows AS from_num_rows
+FROM charges
+LEFT JOIN (
+    SELECT
+        transactions.ledger_id,
+        transaction_items.charge_id,
+        count(*) as num_rows
+    FROM transaction_items
+    INNER JOIN transactions ON transaction_items.transaction_id = transactions.id
+    GROUP BY transactions.ledger_id, transaction_items.charge_id
+) AS from_agg_items
+ON from_agg_items.charge_id = charges.id AND
+   from_agg_items.ledger_id = charges.from_ledger_id
+WHERE charges.to_ledger_id = 2;
+
+set optimizer_switch='split_materialized=on';
+eval $q1;
+eval EXPLAIN $q1;
+eval EXPLAIN FORMAT=JSON $q1;
+
+set optimizer_switch='split_materialized=off';
+eval $q1;
+eval EXPLAIN $q1;
+
+set optimizer_switch='split_materialized=default';
+
+DROP TABLE transaction_items;
+DROP TABLE transactions;
+DROP TABLE charges;
+DROP TABLE ledgers;
+
 --echo # End of 10.3 tests