SQL 语法错误

Question

SELECT 
    CONCAT_WS(' ',child_fname,child_sname) AS 'Child Name'
    , child_gender AS 'Gender'
    , child_dob AS 'DoB'
    , COUNT activity_name AS 'Activities name'
    , CONCAT_WS(' ', parent_title, parent_fname, parent_sname) AS 'Parent Name'
    , parent_phone AS 'Parent phone'
    , CONCAT_WS(' ', parent_address1, parent_address2, parent_town,
        parent_county parent_pcode) AS 'Parent Address',
FROM 
    Child,
    JOIN ChildActivity USING(child_id),
    JOIN Activities USING(activity_id),
    JOIN Parent USING(parent_id),
WHERE 
    activity_name='Art';

查询浏览器说我有 error near 'AS Activities name... CONCAT_WS('',...at line 4.

如何解决此错误？

Answer 1

您的查询中有几个问题。

• 首先，没有CONCAT_WS()功能。我假设您想连接字符串。+如果您使用的是 SQL-Server，请改用运算符：

  child_fname + ' ' + child_sname AS "Child Name",
  

  或者，如果您使用的是 MySQL，则||操作符或CONCAT()函数：

  child_fname || ' ' || child_sname AS "Child Name",
  

  或（更正，更新），只需保留该CONCAT_WS()功能，它适合您的情况，如果您使用的是 MySQL。

• 其次，在错误的地方（在FROMand 和JOIN关键字之前）有几个逗号。

• 第三，别名应该用双引号（如:）"Child Name"或方括号（如:）引用，或者[Child Name]如果它们没有特殊字符并且没​​有保留（如:），则根本不引用Gender。不要对列或表别名使用单引号。单引号用于字符串文字，例如'Art'. MySQL 也可能允许您在别名中使用它们，但不要陷入这种坏习惯。
• 第四，COUNT()是一个（聚合）函数，它需要括号。但既然你没有GROUP BY，那么使用COUNT().
• 最后，SQL-Server 不喜欢USING连接的语法，所以使用ON代替（它适用于所有 DBMS）。

因此，查询变为：

SELECT 
    CONCAT_WS(' ', child_fname, child_sname) AS "Child Name",
    child_gender AS Gender,
    child_dob AS DoB,
    activity_name AS "Activities name",
    CONCAT_WS(' ', parent_title, parent_fname, parent_sname) AS "Parent Name",
    parent_phone AS "Parent phone",
    CONCAT_WS(' ', parent_address1, parent_address2, parent_town, parent_county, parent_pcode)
      AS "Parent Address"                 --<-- Comma removed here.

--- for MySQL
FROM Child                                --<-- Also here
  JOIN ChildActivity USING(child_id)      --<-- and here
  JOIN Activities USING(activity_id)      --<-- and here
  JOIN Parent USING(parent_id)            --<-- and here.

--- for SQL-Server or MySQL
--- FROM Child 
---   JOIN ChildActivity ON ChildActivity.child_id = Child.child_id  
---   JOIN Activities ON Activities.activity_id = ChildActivity.activity_id  
---   JOIN Parent ON Parent.parent_id = Child.parent_id     

WHERE activity_name = 'Art' ;