SELECT 

	( select 1

           from (

               select project_id, spent_on from time_entries

               group by project_id, spent_on

            ) te

            where te.project_id = contract.projects_id

) o

FROM `contract`

GROUP BY `contract`.`id`

CREATE TABLE `contract` (

  `id` int(11) NOT NULL,

  `projects_id` int(11) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

CREATE TABLE `time_entries` (

  `id` int(11) NOT NULL,

  `project_id` int(11) NOT NULL,

  `spent_on` date NOT NULL

) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

ALTER TABLE `contract`

  ADD PRIMARY KEY (`id`),

  ADD KEY `projects_id` (`projects_id`);

ALTER TABLE `time_entries`

  ADD PRIMARY KEY (`id`),

  ADD KEY `project_id` (`project_id`);

ALTER TABLE `contract`

  MODIFY `id` int(11) NOT NULL AUTO_INCREMENT;

ALTER TABLE `time_entries`

  MODIFY `id` int(11) NOT NULL AUTO_INCREMENT;

Thread pointer: 0x7f03ac000c68

Attempting backtrace. You can use the following information to find out

where mysqld died. If you see no messages after this, something went

terribly wrong...

stack_bottom = 0x7f041818ccb8 thread_stack 0x30000

/usr/sbin/mariadbd(my_print_stacktrace+0x2e)[0x562b56c6ecfe]

/usr/sbin/mariadbd(handle_fatal_signal+0x2c3)[0x562b567dc683]

/lib/x86_64-linux-gnu/libc.so.6(+0x3bf90)[0x7f042b45af90]

/usr/sbin/mariadbd(_ZN13st_join_table21choose_best_splittingEjyPy+0x640)[0x562b56760230]

/usr/sbin/mariadbd(_Z16best_access_pathP4JOINP13st_join_tableyPK8POSITIONjbdPS3_S6_+0x169)[0x562b565ebb49]

/usr/sbin/mariadbd(+0x83b744)[0x562b565ef744]

/usr/sbin/mariadbd(+0x83fcaa)[0x562b565f3caa]

/usr/sbin/mariadbd(_Z11choose_planP4JOINy+0x318)[0x562b565f5298]

/usr/sbin/mariadbd(+0x862fef)[0x562b56616fef]

/usr/sbin/mariadbd(_ZN4JOIN14optimize_innerEv+0x1395)[0x562b5661bd95]

/usr/sbin/mariadbd(_ZN4JOIN8optimizeEv+0xaa)[0x562b5661c32a]

/usr/sbin/mariadbd(_ZN13st_select_lex31optimize_unflattened_subqueriesEb+0xe4)[0x562b565830a4]

/usr/sbin/mariadbd(_ZN4JOIN15optimize_stage2Ev+0x1707)[0x562b56619547]

/usr/sbin/mariadbd(_ZN4JOIN14optimize_innerEv+0x1492)[0x562b5661be92]

/usr/sbin/mariadbd(_ZN4JOIN8optimizeEv+0xaa)[0x562b5661c32a]

/usr/sbin/mariadbd(_Z12mysql_selectP3THDP10TABLE_LISTR4ListI4ItemEPS4_jP8st_orderS9_S7_S9_yP13select_resultP18st_select_lex_unitP13st_select_lex+0xca)[0x562b5661c40a]

/usr/sbin/mariadbd(_Z13handle_selectP3THDP3LEXP13select_resulty+0x13f)[0x562b5661cbef]

/usr/sbin/mariadbd(+0x7e8860)[0x562b5659c860]

/usr/sbin/mariadbd(_Z21mysql_execute_commandP3THDb+0x3dc5)[0x562b565a9125]

/usr/sbin/mariadbd(_Z11mysql_parseP3THDPcjP12Parser_state+0x1b5)[0x562b565aa5e5]

/usr/sbin/mariadbd(_Z16dispatch_command19enum_server_commandP3THDPcjb+0x1005)[0x562b565ac515]

/usr/sbin/mariadbd(_Z10do_commandP3THDb+0x137)[0x562b565adb27]

/usr/sbin/mariadbd(_Z24do_handle_one_connectionP7CONNECTb+0x3b7)[0x562b566be7b7]

/usr/sbin/mariadbd(handle_one_connection+0x5d)[0x562b566beb4d]

/usr/sbin/mariadbd(+0xc2d630)[0x562b569e1630]

/lib/x86_64-linux-gnu/libc.so.6(+0x88fd4)[0x7f042b4a7fd4]

/lib/x86_64-linux-gnu/libc.so.6(+0x1095bc)[0x7f042b5285bc]

Trying to get some variables.

Some pointers may be invalid and cause the dump to abort.

Query (0x7f03ac010fc0): SELECT

        ( select 1

           from (

               select project_id, spent_on from time_entries

               group by project_id, spent_on

            ) te

            where te.project_id = contract.projects_id

) o

FROM `contract`

GROUP BY `contract`.`id` LIMIT 0, 25