Bug#39843 DELETE requires write access to table in subquery in where clause

An unnecessarily restrictive lock were taken on sub-SELECTs during DELETE.

During parsing, a global structure is reused for sub-SELECTs and the attribute
keeping track of lock options were not reset properly.
This patch introduces a new attribute to keep track on the syntactical lock
option elements found in a sub-SELECT and then sets the lock options accordingly.

Now the sub-SELECTs will try to acquire a READ lock if possible
instead of a WRITE lock as inherited from the outer DELETE statement.


mysql-test/r/lock.result:
  Added test case for bug39843
mysql-test/t/lock.test:
  Added test case for bug39843
sql/sql_lex.cc:
  * Reset member variable lock_option on each new query.
sql/sql_lex.h:
  * Introduced new member variable 'lock_option' which is keeping track
    of the syntactical lock option of a (sub-)select query.
sql/sql_parse.cc:
  * Wrote comments to functions.
sql/sql_yacc.yy:
  * Introduced an attribute to keep track of syntactical lock options
    in sub-selects.
  * Made sure that the default value TL_READ_DEFAULT is at the begining
    of each subselect-rule.

1 files changed, 27 insertions, 0 deletions

diff --git a/mysql-test/r/lock.result b/mysql-test/r/lock.result
index 6152e403637..7ec07fb5273 100644
--- a/mysql-test/r/lock.result
+++ b/mysql-test/r/lock.result
@@ -166,4 +166,31 @@ ERROR HY000: View's SELECT refers to a temporary table 't2'
 Cleanup.
 
 drop table t2, t3;
+#
+# Bug#39843 DELETE requires write access to table in subquery in where clause
+#
+DROP TABLE IF EXISTS t1,t2;
+CREATE TABLE t1 (
+table1_rowid SMALLINT NOT NULL
+);
+CREATE TABLE t2 (
+table2_rowid SMALLINT NOT NULL
+);
+INSERT INTO t1 VALUES (1);
+INSERT INTO t2 VALUES (1);
+LOCK TABLES t1 WRITE, t2 READ;
+# Sub-select should not try to aquire a write lock.
+DELETE FROM t1 
+WHERE EXISTS 
+( 
+SELECT 'x' 
+FROM t2
+WHERE t1.table1_rowid = t2.table2_rowid
+) ;
+# While implementing the patch we didn't break old behavior;
+# The following sub-select should still requires a write lock:
+SELECT * FROM t1 WHERE 1 IN (SELECT * FROM t2 FOR UPDATE);
+ERROR HY000: Table 't2' was locked with a READ lock and can't be updated
+UNLOCK TABLES;
+DROP TABLE t1,t2;
 End of 5.1 tests.