MAX (Transact-SQL)

傳回運算式中的最大值。 後面可能接著 OVER 子句。

Transact-SQL 語法慣例

語法

MAX ( [ ALL | DISTINCT ] expression )  

引數

• ALL
  將彙總函式套用至所有值。 ALL 是預設值。

• DISTINCT
  指定要考量每個唯一值。 DISTINCT 對 MAX 沒意義，只是為了與 ISO 相容。

• expression
  這是一個常數、資料行名稱或函數，或算術、位元和字串運算子的任何組合。 MAX 可與 numeric、character、uniqueidentifier 和 datetime 資料行並用，但不可與 bit 資料行並用。 不允許彙總函式和子查詢。

  如需詳細資訊，請參閱＜運算式 (Transact-SQL)＞。

傳回類型

傳回與 expression 相同的值。

備註

MAX 會忽略任何 Null 值。

如果是字元資料行，MAX 會在定序順序中尋找最高值。

範例

A.簡單範例

下列範例會傳回最高 (最大) 稅率。

USE AdventureWorks2012;
GO
SELECT MAX(TaxRate)
FROM Sales.SalesTaxRate;
GO

以下為結果集：

-------------------

19.60

Warning, null value eliminated from aggregate.

(1 row(s) affected)

B.使用 OVER 子句

下列範例會將 MIN、MAX、AVG 和 COUNT 函數搭配 OVER 子句一起使用，為 HumanResources.Department 資料表中各部門提供彙總值。

USE AdventureWorks2012; 
GO
SELECT DISTINCT Name
       , MIN(Rate) OVER (PARTITION BY edh.DepartmentID) AS MinSalary
       , MAX(Rate) OVER (PARTITION BY edh.DepartmentID) AS MaxSalary
       , AVG(Rate) OVER (PARTITION BY edh.DepartmentID) AS AvgSalary
       ,COUNT(edh.BusinessEntityID) OVER (PARTITION BY edh.DepartmentID) AS EmployeesPerDept
FROM HumanResources.EmployeePayHistory AS eph
JOIN HumanResources.EmployeeDepartmentHistory AS edh
     ON eph.BusinessEntityID = edh.BusinessEntityID
JOIN HumanResources.Department AS d
 ON d.DepartmentID = edh.DepartmentID
WHERE edh.EndDate IS NULL
ORDER BY Name;

以下為結果集：

Name                          MinSalary             MaxSalary             AvgSalary             EmployeesPerDept
----------------------------- --------------------- --------------------- --------------------- ----------------
Document Control              10.25                 17.7885               14.3884               5
Engineering                   32.6923               63.4615               40.1442               6
Executive                     39.06                 125.50                68.3034               4
Facilities and Maintenance    9.25                  24.0385               13.0316               7
Finance                       13.4615               43.2692               23.935                10
Human Resources               13.9423               27.1394               18.0248               6
Information Services          27.4038               50.4808               34.1586               10
Marketing                     13.4615               37.50                 18.4318               11
Production                    6.50                  84.1346               13.5537               195
Production Control            8.62                  24.5192               16.7746               8
Purchasing                    9.86                  30.00                 18.0202               14
Quality Assurance             10.5769               28.8462               15.4647               6
Research and Development      40.8654               50.4808               43.6731               4
Sales                         23.0769               72.1154               29.9719               18
Shipping and Receiving        9.00                  19.2308               10.8718               6
Tool Design                   8.62                  29.8462               23.5054               6

 (16 row(s) affected)

請參閱

參考

彙總函式 (Transact-SQL)

OVER 子句 (Transact-SQL)