MySQL：左连接问题，返回的记录太多

我在MySQL中得到了以下shema

表“项目”

表“项目关系”

表“子项”

表“评论”

因此，我希望通过SQL查询返回以下数据：

• 项目编号
• 名字
• 描述
• 评论数
• JSON格式的子数据

下面是我正在做的，但JSON数据看起来是乘以行数、注释数或子行数

SELECT i.item_id, i.name, i.description, count(comment_id) as nb_comm,
CONCAT('[', GROUP_CONCAT(CONCAT_WS('','{"color":"', color, '", "weight":"', weight,'"}')), ']') as data
FROM items i
LEFT JOIN comments c ON c.parent_id = i.item_id
LEFT JOIN items_relations ir ON ir.item_id = i.item_id
LEFT JOIN children ch ON ir.child_id = ch.children_id
WHERE 1

数据场包含

[{"color":"blue", "weight":"5"},{"color":"blue", "weight":"5"},{"color":"red", "weight":"10"},{"color":"red", "weight":"10"}]

如何在数据字段中包含正确的内容

---

这是一个

您可以使用DISTINCT进行分组计数

SELECT i.item_id, i.name, i.description, count(distinct comment_id) as nb_comm,
CONCAT('[', GROUP_CONCAT(DISTINCT CONCAT_WS('','{"color":"', color, '", "weight":"', weight,'"}')), ']') as data
FROM items i
LEFT JOIN comments c ON c.parent_id = i.item_id
LEFT JOIN items_relations ir ON ir.item_id = i.item_id
LEFT JOIN children ch ON ir.child_id = ch.children_id
GROUP BY i.item_id, i.name, i.description

---

您可以使用DISTINCT进行分组和计数

SELECT i.item_id, i.name, i.description, count(distinct comment_id) as nb_comm,
CONCAT('[', GROUP_CONCAT(DISTINCT CONCAT_WS('','{"color":"', color, '", "weight":"', weight,'"}')), ']') as data
FROM items i
LEFT JOIN comments c ON c.parent_id = i.item_id
LEFT JOIN items_relations ir ON ir.item_id = i.item_id
LEFT JOIN children ch ON ir.child_id = ch.children_id
GROUP BY i.item_id, i.name, i.description

---

您正在运行哪个版本的MySQL？实际上是MariaDB 10.3您正在运行哪个版本的MySQL？实际上是MariaDB 10.3是的！这解决了数据问题，但评论的数量仍然是错误的。是的！这解决了数据问题，但评论的数量仍然是错误的。

SELECT i.item_id, i.name, i.description, count(comment_id) as nb_comm,
CONCAT('[', GROUP_CONCAT(CONCAT_WS('','{"color":"', color, '", "weight":"', weight,'"}')), ']') as data
FROM items i
LEFT JOIN comments c ON c.parent_id = i.item_id
LEFT JOIN items_relations ir ON ir.item_id = i.item_id
LEFT JOIN children ch ON ir.child_id = ch.children_id
WHERE 1

[{"color":"blue", "weight":"5"},{"color":"blue", "weight":"5"},{"color":"red", "weight":"10"},{"color":"red", "weight":"10"}]

SELECT i.item_id, i.name, i.description, count(distinct comment_id) as nb_comm,
CONCAT('[', GROUP_CONCAT(DISTINCT CONCAT_WS('','{"color":"', color, '", "weight":"', weight,'"}')), ']') as data
FROM items i
LEFT JOIN comments c ON c.parent_id = i.item_id
LEFT JOIN items_relations ir ON ir.item_id = i.item_id
LEFT JOIN children ch ON ir.child_id = ch.children_id
GROUP BY i.item_id, i.name, i.description