MySQL JSON_OBJECT instead of GROUP_CONCAT - mysql

Question

I have the following sql query that works fine using GROUP_CONCAT:
SELECT orders.created_at,products.title, o_p.qty AS qty,
(SELECT GROUP_CONCAT(features.title,"\:", o_p_f.value, features.unit) FROM order_product_features AS o_p_f
LEFT JOIN product_features ON product_features.id = o_p_f.product_feature_id
LEFT JOIN features ON o_p_f.product_feature_id = product_features.id
AND features.id = product_features.feature_id
WHERE o_p_f.order_product_id = o_p.id
) AS prop
FROM orders
LEFT JOIN order_products AS o_p ON o_p.order_id = orders.id
LEFT JOIN products ON products.id = o_p.product_id
The above query returns result looks like the following screen shot:
Now, I want to replace GROUP_CONCAT with JSON_OBJECT or in other words, I want to have prop field to be JSON object. I have tried the following:
SELECT orders.created_at,products.title, o_p.qty AS qty,
JSON_OBJECT((SELECT GROUP_CONCAT("title",features.title,"value", o_p_f.value, 'unit',features.unit) FROM order_product_features AS o_p_f
LEFT JOIN product_features ON product_features.id = o_p_f.product_feature_id
LEFT JOIN features ON o_p_f.product_feature_id = product_features.id
AND features.id = product_features.feature_id
WHERE o_p_f.order_product_id = o_p.id
)) AS prop
FROM orders
LEFT JOIN order_products AS o_p ON o_p.order_id = orders.id
LEFT JOIN products ON products.id = o_p.product_id
However, the above query returns error:
1582 - Incorrect parameter count in the call to native function 'JSON_OBJECT'

Answer 1

On ≥ 5.7.22
JSON_OBJECTAGG(key, value) is more likely what you're after.
mysql> SELECT o_id, attribute, value FROM t3;
+------+-----------+-------+
| o_id | attribute | value |
+------+-----------+-------+
| 2 | color | red |
| 2 | fabric | silk |
| 3 | color | green |
| 3 | shape | square|
+------+-----------+-------+
4 rows in set (0.00 sec)
mysql> SELECT o_id, JSON_OBJECTAGG(attribute, value) FROM t3 GROUP BY o_id;
+------+----------------------------------------+
| o_id | JSON_OBJECTAGG(attribute, name) |
+------+----------------------------------------+
| 2 | {"color": "red", "fabric": "silk"} |
| 3 | {"color": "green", "shape": "square"} |
+------+----------------------------------------+
1 row in set (0.00 sec)
But as you don't provide your table structure I can't help you with the query.
It seem your handling of unit will grant you some extra work, as aggregate function use Key=>Value and will not take a third argument...
On ≥ 5.7
You'll have to make a bit of hand craft:
SELECT
o_id,
CONCAT(
'{',
GROUP_CONCAT(
TRIM(
LEADING '{' FROM TRIM(
TRAILING '}' FROM JSON_OBJECT(
`attribute`,
`value`
)
)
)
),
'}'
) json
FROM t3
GROUP BY o_id
≥ 5.5
Without any JSON function:
SELECT
o_id,
CONCAT(
'{',
GROUP_CONCAT(
CONCAT(
'"',
`attribute`,
'":"',
`value`,
'"'
)
),
'}'
) json
FROM t3
GROUP BY o_id