diff --git a/mysql-test/r/join_outer.result b/mysql-test/r/join_outer.result
index 1366a8fe97a..31539b68069 100644
--- a/mysql-test/r/join_outer.result
+++ b/mysql-test/r/join_outer.result
@@ -1254,3 +1254,33 @@ SELECT * FROM t1 LEFT JOIN t2 ON e<>0 WHERE c=1 AND d<=>NULL;
c e d
1 0 NULL
DROP TABLE t1,t2;
+#
+# Bug#52357: Assertion failed: join->best_read in greedy_search
+# optimizer_search_depth=0
+#
+CREATE TABLE t1( a INT );
+INSERT INTO t1 VALUES (1),(2);
+SET optimizer_search_depth = 0;
+# Should not core dump on query preparation
+EXPLAIN
+SELECT 1
+FROM t1 tt3 LEFT OUTER JOIN t1 tt4 ON 1
+LEFT OUTER JOIN t1 tt5 ON 1
+LEFT OUTER JOIN t1 tt6 ON 1
+LEFT OUTER JOIN t1 tt7 ON 1
+LEFT OUTER JOIN t1 tt8 ON 1
+RIGHT OUTER JOIN t1 tt2 ON 1
+RIGHT OUTER JOIN t1 tt1 ON 1
+STRAIGHT_JOIN t1 tt9 ON 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE tt1 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt2 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt3 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt4 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt5 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt6 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt7 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt8 ALL NULL NULL NULL NULL 2
+1 SIMPLE tt9 ALL NULL NULL NULL NULL 2
+SET optimizer_search_depth = DEFAULT;
+DROP TABLE t1;
diff --git a/mysql-test/t/join_outer.test b/mysql-test/t/join_outer.test
index 1a59dbf8fc2..0d75ac97266 100644
--- a/mysql-test/t/join_outer.test
+++ b/mysql-test/t/join_outer.test
@@ -861,3 +861,27 @@ SELECT * FROM t1 LEFT JOIN t2 ON e<>0 WHERE c=1 AND d<=>NULL;
DROP TABLE t1,t2;
+
+--echo #
+--echo # Bug#52357: Assertion failed: join->best_read in greedy_search
+--echo # optimizer_search_depth=0
+--echo #
+CREATE TABLE t1( a INT );
+
+INSERT INTO t1 VALUES (1),(2);
+SET optimizer_search_depth = 0;
+
+--echo # Should not core dump on query preparation
+EXPLAIN
+SELECT 1
+FROM t1 tt3 LEFT OUTER JOIN t1 tt4 ON 1
+ LEFT OUTER JOIN t1 tt5 ON 1
+ LEFT OUTER JOIN t1 tt6 ON 1
+ LEFT OUTER JOIN t1 tt7 ON 1
+ LEFT OUTER JOIN t1 tt8 ON 1
+ RIGHT OUTER JOIN t1 tt2 ON 1
+ RIGHT OUTER JOIN t1 tt1 ON 1
+ STRAIGHT_JOIN t1 tt9 ON 1;
+
+SET optimizer_search_depth = DEFAULT;
+DROP TABLE t1;
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index f0177893840..53a6b699022 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -8706,6 +8706,39 @@ static bool check_interleaving_with_nj(JOIN_TAB *next_tab)
/*
Nested joins perspective: Remove the last table from the join order
+ The algorithm is the reciprocal of check_interleaving_with_nj(), hence
+ parent join nest nodes are updated only when the last table in its child
+ node is removed. The ASCII graphic below will clarify.
+
+ %A table nesting such as t1 x [ ( t2 x t3 ) x ( t4 x t5 ) ] is
+ represented by the below join nest tree.
+
+ @verbatim
+ NJ1
+ _/ / \
+ _/ / NJ2
+ _/ / / \
+ / / / \
+ t1 x [ (t2 x t3) x (t4 x t5) ]
+ @endverbatim
+
+ At the point in time when check_interleaving_with_nj() adds the table t5 to
+ the query execution plan, QEP, it also directs the node named NJ2 to mark
+ the table as covered. NJ2 does so by incrementing its @c counter
+ member. Since all of NJ2's tables are now covered by the QEP, the algorithm
+ proceeds up the tree to NJ1, incrementing its counter as well. All join
+ nests are now completely covered by the QEP.
+
+ restore_prev_nj_state() does the above in reverse. As seen above, the node
+ NJ1 contains the nodes t2, t3, and NJ2. Its counter being equal to 3 means
+ that the plan covers t2, t3, and NJ2, @e and that the sub-plan (t4 x t5)
+ completely covers NJ2. The removal of t5 from the partial plan will first
+ decrement NJ2's counter to 1. It will then detect that NJ2 went from being
+ completely to partially covered, and hence the algorithm must continue
+ upwards to NJ1 and decrement its counter to 2. %A subsequent removal of t4
+ will however not influence NJ1 since it did not un-cover the last table in
+ NJ2.
+
SYNOPSIS
restore_prev_nj_state()
last join table to remove, it is assumed to be the last in current
@@ -8722,19 +8755,20 @@ static void restore_prev_nj_state(JOIN_TAB *last)
{
TABLE_LIST *last_emb= last->table->pos_in_table_list->embedding;
JOIN *join= last->join;
- while (last_emb)
+ for (;last_emb != NULL; last_emb= last_emb->embedding)
{
- if (!(--last_emb->nested_join->counter))
- join->cur_embedding_map&= ~last_emb->nested_join->nj_map;
- else if (last_emb->nested_join->join_list.elements-1 ==
- last_emb->nested_join->counter)
- {
- join->cur_embedding_map|= last_emb->nested_join->nj_map;
+ NESTED_JOIN *nest= last_emb->nested_join;
+ DBUG_ASSERT(nest->counter > 0);
+
+ bool was_fully_covered= nest->is_fully_covered();
+
+ if (--nest->counter == 0)
+ join->cur_embedding_map&= ~nest->nj_map;
+
+ if (!was_fully_covered)
break;
- }
- else
- break;
- last_emb= last_emb->embedding;
+
+ join->cur_embedding_map|= nest->nj_map;
}
}
diff --git a/sql/table.h b/sql/table.h
index db996d45320..f162c2ed8ca 100644
--- a/sql/table.h
+++ b/sql/table.h
@@ -910,7 +910,11 @@ typedef struct st_nested_join
List join_list; /* list of elements in the nested join */
table_map used_tables; /* bitmap of tables in the nested join */
table_map not_null_tables; /* tables that rejects nulls */
- struct st_join_table *first_nested;/* the first nested table in the plan */
+ /**
+ Used for pointing out the first table in the plan being covered by this
+ join nest. It is used exclusively within make_outerjoin_info().
+ */
+ struct st_join_table *first_nested;
/*
Used to count tables in the nested join in 2 isolated places:
1. In make_outerjoin_info().
@@ -920,6 +924,15 @@ typedef struct st_nested_join
*/
uint counter;
nested_join_map nj_map; /* Bit used to identify this nested join*/
+ /**
+ True if this join nest node is completely covered by the query execution
+ plan. This means two things.
+
+ 1. All tables on its @c join_list are covered by the plan.
+
+ 2. All child join nest nodes are fully covered.
+ */
+ bool is_fully_covered() const { return join_list.elements == counter; }
} NESTED_JOIN;