Question

我试图通过加入2个这样的表来创建一个MySQL视图：

用户表：

            var sortedList = from p in marketItems
                             group p by p.ParentGroup into Groups
                             select Groups;
            //to access the items in each group individually
            foreach (var grouping in sortedList)
            {
                foreach (var Item in grouping)
                {
                    Item.Description///you can access the individual items from this layer...
                }
            }

技能表：

+----+------+  
| id | name |
+----+------+
| 1  | Joy  |
+----+------+
| 2  | Roy  |
+----+------+
| 3  | Tony |
+----+------+

技能表格中的+---------+---------+------------+ | auto_id | user_id | skill | +---------+---------+------------+ | 1 | 1 | PHP | +---------+---------+------------+ | 2 | 1 | CSS | +---------+---------+------------+ | 3 | 2 | Ruby | +---------+---------+------------+ | 4 | 2 | Javascript | +---------+---------+------------+是用户表格中user_id的外键。

查询创建视图：

id

现在问题是创建的视图只有2行，我知道它因为 user_id 3 的技能表中没有值。现在我想要的是将 Tony＆＃39; 技能的所有3行作为 Null 值，如下所示：

CREATE OR REPLACE VIEW user_view AS SELECT u.id, u.name,  GROUP_CONCAT(s.skill) as 
skills FROM users u, skills s WHERE u.id = s.user_id GROUP BY u.id

Answer 1

您正在寻找Left join：

CREATE OR REPLACE VIEW user_view AS
    SELECT 
        u.id,
        u.name,
        GROUP_CONCAT(s.skill) AS skills
    FROM
        users u
            LEFT JOIN
        skills s ON u.id = s.user_id
    GROUP BY u.id

在MySQL中创建一个具有空值的VIEW

1 个答案: