[gmontee@localhost ~]$ mysql -u root --execute='SELECT version();'
+-----------------+
| version()       |
+-----------------+
| 10.0.15-MariaDB |
+-----------------+
[gmontee@localhost ~]$ mysql -u root < optimizer_search_depth_semijoin_data_setup.sql
[gmontee@localhost ~]$ mysql -u root < optimizer_search_depth_semijoin_query_test.sql
test_type
semijoin=ON, optimizer_search_depth=1
id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra
1       PRIMARY T3_0_   ref     PRIMARY,FK_T3_T2Id      PRIMARY 8       const   3       Using index
1       PRIMARY T2_1_   eq_ref  PRIMARY,FK_T2_T1Id      PRIMARY 8       semijoin_test.T3_0_.T2IdRef     1
1       PRIMARY T1_1_   eq_ref  PRIMARY PRIMARY 8       semijoin_test.T2_1_.T1IdRef     1       Using index
1       PRIMARY T2_0_   ref     FK_T2_T1Id      FK_T2_T1Id      8       semijoin_test.T2_1_.T1IdRef     1       Using index
T1IdRef T2Id
200001  200011
200001  200012
200001  200013
200001  200011
200001  200012
200001  200013
200001  200011
200001  200012
200001  200013
test_type
semijoin=ON, optimizer_search_depth=3
id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra
1       PRIMARY T3_0_   ref     PRIMARY,FK_T3_T2Id      PRIMARY 8       const   3       Using index; Start temporary
1       PRIMARY T2_1_   eq_ref  PRIMARY,FK_T2_T1Id      PRIMARY 8       semijoin_test.T3_0_.T2IdRef     1
1       PRIMARY T1_1_   eq_ref  PRIMARY PRIMARY 8       semijoin_test.T2_1_.T1IdRef     1       Using index
1       PRIMARY T2_0_   ref     FK_T2_T1Id      FK_T2_T1Id      8       semijoin_test.T2_1_.T1IdRef     1       Using index; End temporary
T1IdRef T2Id
200001  200011
200001  200012
200001  200013
test_type
semijoin=OFF, optimizer_search_depth=1
id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra
1       PRIMARY T2_0_   index   NULL    FK_T2_T1Id      8       NULL    27      Using where; Using index
2       MATERIALIZED    T3_0_   ref     PRIMARY,FK_T3_T2Id      PRIMARY 8       const   3       Using index
2       MATERIALIZED    T2_1_   eq_ref  PRIMARY,FK_T2_T1Id      PRIMARY 8       semijoin_test.T3_0_.T2IdRef     1
2       MATERIALIZED    T1_1_   eq_ref  PRIMARY PRIMARY 8       semijoin_test.T2_1_.T1IdRef     1       Using index
T1IdRef T2Id
200001  200011
200001  200012
200001  200013
test_type
semijoin=OFF, optimizer_search_depth=3
id      select_type     table   type    possible_keys   key     key_len ref     rows    Extra
1       PRIMARY T2_0_   index   NULL    FK_T2_T1Id      8       NULL    27      Using where; Using index
2       MATERIALIZED    T3_0_   ref     PRIMARY,FK_T3_T2Id      PRIMARY 8       const   3       Using index
2       MATERIALIZED    T2_1_   eq_ref  PRIMARY,FK_T2_T1Id      PRIMARY 8       semijoin_test.T3_0_.T2IdRef     1
2       MATERIALIZED    T1_1_   eq_ref  PRIMARY PRIMARY 8       semijoin_test.T2_1_.T1IdRef     1       Using index
T1IdRef T2Id
200001  200011
200001  200012
200001  200013