Populate t1 in order to get more predictable explain results.

mysql-test/r/subselect2.result

@@ -14,6 +14,7 @@ DOCID VARCHAR(32)BINARY NOT NULL
 , PRIMARY KEY ( DOCID )
 ) ENGINE=InnoDB
 ;
+INSERT INTO t1 (DOCID) VALUES ("1"), ("2");
 CREATE TABLE t2
 (
 DOCID VARCHAR(32)BINARY NOT NULL

mysql-test/t/subselect2.test

@@ -25,6 +25,8 @@ DOCID VARCHAR(32)BINARY NOT NULL
 ) ENGINE=InnoDB
 ;
 
+INSERT INTO t1 (DOCID) VALUES ("1"), ("2");
+
 CREATE TABLE t2
 (
 DOCID VARCHAR(32)BINARY NOT NULL