From 9c3eca85141836548214e3c68f256b3868502509 Mon Sep 17 00:00:00 2001
From: Sergei Petrunia <psergey@askmonty.org>
Date: Sat, 7 Dec 2019 18:21:36 +0300
Subject: [PATCH] MDEV-21243: Join buffer: condition is checked in wrong place
 for range access

In this scenario:
- There is a possible range access for table T
- And there is a ref access on the same index which uses fewer key parts
- The join optimizer picks the ref access (because it is cheaper)
- make_join_select applies this heuristic to switch to range:
  /* Range uses longer key;  Use this instead of ref on key */

Join buffer will be used without having called
JOIN_TAB::make_scan_filter(). This means, conditions that should be
checked when reading table T will be checked after T is joined with the
contents of the join buffer, instead.

Fixed this by adding a make_scan_filter() check.
(updated patch after backport to 10.3)
(Fix testcase on Windows)
---
 mysql-test/main/join_cache.result | 72 +++++++++++++++++++++++++++++++
 mysql-test/main/join_cache.test   | 40 +++++++++++++++++
 sql/sql_select.cc                 | 10 +++++
 3 files changed, 122 insertions(+)

diff --git a/mysql-test/main/join_cache.result b/mysql-test/main/join_cache.result
index bab32395413f5..3d1d91df997b5 100644
--- a/mysql-test/main/join_cache.result
+++ b/mysql-test/main/join_cache.result
@@ -6056,4 +6056,76 @@ select f2 from t2,t1 where f2 = 0;
 f2
 drop table t1, t2;
 set join_buffer_size=@save_join_buffer_size;
+#
+# MDEV-21243: Join buffer: condition is checked in wrong place for range access
+#
+create table t1(a int primary key);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2 (a int);
+insert into t2 select A.a + 10*B.a from t1 A, t1 B;
+create table t3 (
+kp1 int,
+kp2 int,
+col1 int,
+col2 int,
+key (kp1, kp2)
+);
+insert into t3
+select
+A.a,
+B.a,
+A.a + 100*B.a,
+A.a + 100*B.a
+from
+t2 A, t2 B;
+analyze table t3;
+Table	Op	Msg_type	Msg_text
+test.t3	analyze	status	Table is already up to date
+# The following must have "B.col1 + 1 < 33333" attached to table B
+# and not to the block-nl-join node:
+explain format=json
+select *
+from t1 a, t3 b
+where
+b.kp1=a.a and
+b.kp1 <= 10 and
+b.kp2 <= 10 and
+b.col1 +1 < 33333;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "a",
+      "access_type": "index",
+      "possible_keys": ["PRIMARY"],
+      "key": "PRIMARY",
+      "key_length": "4",
+      "used_key_parts": ["a"],
+      "rows": 10,
+      "filtered": 100,
+      "attached_condition": "a.a <= 10",
+      "using_index": true
+    },
+    "block-nl-join": {
+      "table": {
+        "table_name": "b",
+        "access_type": "range",
+        "possible_keys": ["kp1"],
+        "key": "kp1",
+        "key_length": "10",
+        "used_key_parts": ["kp1", "kp2"],
+        "rows": 836,
+        "filtered": 11.962,
+        "index_condition": "b.kp2 <= 10",
+        "attached_condition": "b.kp2 <= 10 and b.col1 + 1 < 33333"
+      },
+      "buffer_type": "flat",
+      "buffer_size": "256Kb",
+      "join_type": "BNL",
+      "attached_condition": "b.kp1 = a.a"
+    }
+  }
+}
+drop table t1,t2,t3;
 set @@optimizer_switch=@save_optimizer_switch;
diff --git a/mysql-test/main/join_cache.test b/mysql-test/main/join_cache.test
index 9576d5981259a..91339c2cb2165 100644
--- a/mysql-test/main/join_cache.test
+++ b/mysql-test/main/join_cache.test
@@ -4014,5 +4014,45 @@ select f2 from t2,t1 where f2 = 0;
 drop table t1, t2;
 set join_buffer_size=@save_join_buffer_size;
 
+
+--echo #
+--echo # MDEV-21243: Join buffer: condition is checked in wrong place for range access
+--echo #
+create table t1(a int primary key);
+insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+create table t2 (a int);
+insert into t2 select A.a + 10*B.a from t1 A, t1 B;
+
+create table t3 (
+  kp1 int,
+  kp2 int,
+  col1 int,
+  col2 int,
+  key (kp1, kp2)
+);
+
+insert into t3
+select
+  A.a,
+  B.a,
+  A.a + 100*B.a,
+  A.a + 100*B.a
+from
+  t2 A, t2 B;
+analyze table t3;
+
+--echo # The following must have "B.col1 + 1 < 33333" attached to table B
+--echo # and not to the block-nl-join node:
+explain format=json
+select *
+from t1 a, t3 b
+where
+  b.kp1=a.a and
+  b.kp1 <= 10 and
+  b.kp2 <= 10 and
+  b.col1 +1 < 33333;
+
+drop table t1,t2,t3;
+
 # The following command must be the last one in the file 
 set @@optimizer_switch=@save_optimizer_switch;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index da8dfdd015af5..76cad16de28d2 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -10966,6 +10966,13 @@ make_join_select(JOIN *join,SQL_SELECT *select,COND *cond)
 	  if (i != join->const_tables && tab->use_quick != 2 &&
               !tab->first_inner)
 	  {					/* Read with cache */
+            /*
+              TODO: the execution also gets here when we will not be using
+              join buffer. Review these cases and perhaps, remove this call.
+              (The final decision whether to use join buffer is made in
+              check_join_cache_usage, so we should only call make_scan_filter()
+              there, too).
+            */
             if (tab->make_scan_filter())
               DBUG_RETURN(1);
           }
@@ -11928,6 +11935,9 @@ uint check_join_cache_usage(JOIN_TAB *tab,
     if ((tab->cache= new (root) JOIN_CACHE_BNL(join, tab, prev_cache)))
     {
       tab->icp_other_tables_ok= FALSE;
+      /* If make_join_select() hasn't called make_scan_filter(), do it now */
+      if (!tab->cache_select && tab->make_scan_filter())
+        goto no_join_cache;
       return (2 - MY_TEST(!prev_cache));
     }
     goto no_join_cache;