Question

这是我的sql语句我得到了这个错误。但是当我只使用Max来单独而不显示其他结果时它会起作用。有人可以帮助我

SELECT cat.CategoryName,sb.SubCategoryName,MAX((COUNT(bs.BookID))) 
FROM
  Category cat,SubCategory sb, Book_Subcategory bs 
WHERE cat.CategoryID = sb.CategoryID AND sb.SubCategoryID = bs.SubCategoryID 
GROUP BY cat.CategoryName, sb.SubCategoryName, bs.BookID;

ERROR at line 1:
ORA-00937: not a single-group group function

有人可以帮助我吗？

Answer 1

SQL不允许直接聚合聚合。

但是，如果在FROM子句的子查询中编写内部聚合（或使用WITH子句和公用表表达式CTE），则可以实现结果：

SELECT gc1.CategoryName, gc1.SubCategoryName, gc1.BookCount
  FROM (SELECT cat.CategoryName, sb.SubCategoryName,
               COUNT(bs.BookID) AS BookCount
          FROM Category AS cat
          JOIN SubCategory AS sb ON cat.CategoryID = sb.CategoryID
          JOIN Book_Subcategory AS bs ON sb.SubCategoryID = bs.SubCategoryID
         GROUP BY cat.CategoryName, sb.SubCategoryName
       ) AS gc1
 WHERE gc1.BookCount = (SELECT MAX(gc2.BookCount)
                          FROM (SELECT cat.CategoryName, sb.SubCategoryName,
                                       COUNT(bs.BookID) AS BookCount
                                  FROM Category AS cat
                                  JOIN SubCategory AS sb
                                       ON cat.CategoryID = sb.CategoryID
                                  JOIN Book_Subcategory AS bs
                                       ON sb.SubCategoryID = bs.SubCategoryID
                                 GROUP BY cat.CategoryName, sb.SubCategoryName
                                ) AS gc2
                        )

这很复杂，因为它不使用CTE，并且有一个必须写出两次的公用表表达式。

使用CTE表格（可能有语法错误）：

WITH gc1 AS (SELECT cat.CategoryName, sb.SubCategoryName,
                    COUNT(bs.BookID) AS BookCount
               FROM Category AS cat
               JOIN SubCategory AS sb
                    ON cat.CategoryID = sb.CategoryID
               JOIN Book_Subcategory AS bs
                    ON sb.SubCategoryID = bs.SubCategoryID
              GROUP BY cat.CategoryName, sb.SubCategoryName
            )
SELECT gc1.CategoryName, gc1.SubCategoryName, gc1.BookCount
  FROM gc1
 WHERE gc1.BookCount = SELECT MAX(gc1.BookCount) FROM gc1);

更整洁！

如果您的DBMS可以轻松创建临时表，则可以使用临时表模拟CTE。例如，IBM Informix Dynamic Server可以使用：

SELECT cat.CategoryName, sb.SubCategoryName,
       COUNT(bs.BookID) AS BookCount
  FROM Category AS cat
  JOIN SubCategory AS sb ON cat.CategoryID = sb.CategoryID
  JOIN Book_Subcategory AS bs ON sb.SubCategoryID = bs.SubCategoryID
 GROUP BY cat.CategoryName, sb.SubCategoryName
  INTO TEMP gc1;

SELECT gc1.CategoryName, gc1.SubCategoryName, gc1.BookCount
  FROM gc1
 WHERE gc1.BookCount = (SELECT MAX(gc1.BookCount) FROM gc1);

DROP TABLE gc1;  -- Optional: table will be deleted at end of session anyway

鉴于以下表和数据，主要查询（从此答案中复制并粘贴）给出了在MacOS X 10.6.4上针对IBM Informix Dynamic Server 11.50.FC6运行时所期望的结果，即：

Non-Fiction    SQL Theory    4
Fiction        War           4

这并不能证明它在针对Oracle运行时“必须工作” - 我没有Oracle，也无法证明这两种方式。它确实表明至少有一个SQL DBMS可以毫无问题地处理查询。（由于IDS不支持WITH子句和CTE，我无法证明该公式是否有效。）

模式

CREATE TABLE Category
(
    CategoryID INTEGER NOT NULL PRIMARY KEY,
    CategoryName VARCHAR(20) NOT NULL
);
CREATE TABLE SubCategory
(
    CategoryID INTEGER NOT NULL REFERENCES Category,
    SubCategoryID INTEGER NOT NULL PRIMARY KEY,
    SubCategoryName VARCHAR(20) NOT NULL
 );
CREATE TABLE Book_SubCategory
(
    SubCategoryID INTEGER NOT NULL REFERENCES SubCategory,
    BookID INTEGER NOT NULL PRIMARY KEY
);

数据

INSERT INTO Category VALUES(1, 'Fiction');
INSERT INTO Category VALUES(2, 'Non-Fiction');

INSERT INTO SubCategory VALUES(2, 1, 'SQL Theory');
INSERT INTO SubCategory VALUES(2, 2, 'Mathematics');
INSERT INTO SubCategory VALUES(1, 3, 'Romance');
INSERT INTO SubCategory VALUES(1, 4, 'War');

INSERT INTO Book_SubCategory VALUES(1, 10);
INSERT INTO Book_SubCategory VALUES(2, 11);
INSERT INTO Book_SubCategory VALUES(3, 12);
INSERT INTO Book_SubCategory VALUES(3, 13);
INSERT INTO Book_SubCategory VALUES(4, 14);
INSERT INTO Book_SubCategory VALUES(1, 15);
INSERT INTO Book_SubCategory VALUES(1, 16);
INSERT INTO Book_SubCategory VALUES(2, 17);
INSERT INTO Book_SubCategory VALUES(1, 18);
INSERT INTO Book_SubCategory VALUES(3, 19);
INSERT INTO Book_SubCategory VALUES(4, 20);
INSERT INTO Book_SubCategory VALUES(4, 21);
INSERT INTO Book_SubCategory VALUES(4, 22);

Answer 2

我认为错误在GROUP BY子句中（bs.BookID不属于那里）：

SELECT cat.CategoryName,sb.SubCategoryName,MAX(COUNT(bs.BookID)) 
FROM Category cat,SubCategory sb, Book_Subcategory bs 
WHERE cat.CategoryID =sb.CategoryID AND sb.SubCategoryID=bs.SubCategoryID 
GROUP BY cat.CategoryName,sb.SubCategoryName;

顺便说一下，空格（和标点符号）是你的朋友。不要对它懒惰。

不能在SQL * Plus中使用Max with Count

2 个答案:

模式

数据