MySQL 8.0

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CREATE TABLE t_o (
  order_id INTEGER UNSIGNED PRIMARY KEY,
  placed_on DATE NOT NULL,
  INDEX (placed_on)
);
INSERT INTO t_o (order_id, placed_on) VALUES
(1, '2018-10-01'),
(2, '2018-10-02');
CREATE TABLE t_oi (
  item_id INTEGER UNSIGNED PRIMARY KEY AUTO_INCREMENT,
  order_id INTEGER UNSIGNED NOT NULL,
  sku VARCHAR(31) CHARACTER SET ascii COLLATE ascii_general_ci NOT NULL,
  qty INTEGER UNSIGNED NOT NULL,
  unit_price INTEGER UNSIGNED NOT NULL,
  INDEX (sku),
  FOREIGN KEY (order_id) REFERENCES t_o (order_id)
    ON DELETE CASCADE ON UPDATE CASCADE
);
INSERT INTO t_oi (order_id, sku, qty, unit_price) VALUES
(1, 'SO', 1, 599),
(1, 'SF', 2, 399),
(2, 'SU', 1, 399);
select @@sql_mode;


@@sql_mode


ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION


/* functioanlly dependent columns only */
SELECT t_oi.order_id, t_o.placed_on
FROM t_o
INNER JOIN t_oi ON t_o.order_id = t_oi.order_id
GROUP BY t_oi.order_id
HAVING COUNT(*) = 1


order_id
placed_on


2
2018-10-02


/* any columns some not functionally dependent */
SELECT t_oi.order_id, t_o.placed_on, t_oi.sku, t_oi.qty, t_oi.unit_price
FROM t_o
INNER JOIN t_oi ON t_o.order_id = t_oi.order_id
GROUP BY t_oi.order_id
HAVING COUNT(*) = 1
Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'fiddle_YRLHCAMPBMVSWYXFQGUD.t_oi.sku' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

SET sql_mode = 'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION'
select @@sql_mode


@@sql_mode


STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION


/* any columns some not functionally dependent */
SELECT t_oi.order_id, t_o.placed_on, t_oi.sku, t_oi.qty, t_oi.unit_price
FROM t_o
INNER JOIN t_oi ON t_o.order_id = t_oi.order_id
GROUP BY t_oi.order_id
HAVING COUNT(*) = 1


order_id
placed_on
sku
qty
unit_price


2
2018-10-02
SU
1
399