SQL Server进阶（十一）可编程对象——变量、 批、流元素、 游标

变量

---------------------------------------------------------------------
-- Variables
---------------------------------------------------------------------

-- Declare a variable and initialize it with a value
DECLARE @i AS INT;
SET @i = 10;
GO

-- Declare and initialize a variable in the same statement
DECLARE @i AS INT = 10;
GO

-- Store the result of a subquery in a variable
DECLARE @empname AS NVARCHAR(31);

SET @empname = (SELECT firstname + N' ' + lastname
                FROM HR.Employees
                WHERE empid = 3);

SELECT @empname AS empname;
GO

-- Using the SET command to assign one variable at a time
DECLARE @firstname AS NVARCHAR(10), @lastname AS NVARCHAR(20);

SET @firstname = (SELECT firstname
                  FROM HR.Employees
                  WHERE empid = 3);
SET @lastname = (SELECT lastname
                  FROM HR.Employees
                  WHERE empid = 3);

SELECT @firstname AS firstname, @lastname AS lastname;
GO

-- Using the SELECT command to assign multiple variables in the same statement
DECLARE @firstname AS NVARCHAR(10), @lastname AS NVARCHAR(20);

SELECT
  @firstname = firstname,
  @lastname  = lastname
FROM HR.Employees
WHERE empid = 3;

SELECT @firstname AS firstname, @lastname AS lastname;
GO

-- SELECT doesn't fail when multiple rows qualify
DECLARE @empname AS NVARCHAR(31);

SELECT @empname = firstname + N' ' + lastname
FROM HR.Employees
WHERE mgrid = 2;

SELECT @empname AS empname;
GO

-- SET fails when multiple rows qualify
DECLARE @empname AS NVARCHAR(31);

SET @empname = (SELECT firstname + N' ' + lastname
                FROM HR.Employees
                WHERE mgrid = 2);

SELECT @empname AS empname;
GO

 批

流元素

IF ... ELSE

-- The IF ... ELSE Flow Element
IF YEAR(SYSDATETIME()) <> YEAR(DATEADD(day, 1, SYSDATETIME()))
  PRINT 'Today is the last day of the year.';
ELSE
  PRINT 'Today is not the last day of the year.';
GO

 IF ELSE IF

-- IF ELSE IF
IF YEAR(SYSDATETIME()) <> YEAR(DATEADD(day, 1, SYSDATETIME()))
  PRINT 'Today is the last day of the year.';
ELSE
  IF MONTH(SYSDATETIME()) <> MONTH(DATEADD(day, 1, SYSDATETIME()))
    PRINT 'Today is the last day of the month but not the last day of the year.';
  ELSE 
    PRINT 'Today is not the last day of the month.';
GO

语句块

-- Statement Block
IF DAY(SYSDATETIME()) = 1
BEGIN
  PRINT 'Today is the first day of the month.';
  PRINT 'Starting first-of-month-day process.';
  /* ... process code goes here ... */
  PRINT 'Finished first-of-month-day database process.';
END
ELSE
BEGIN
  PRINT 'Today is not the first day of the month.';
  PRINT 'Starting non-first-of-month-day process.';
  /* ... process code goes here ... */
  PRINT 'Finished non-first-of-month-day process.';
END
GO

 WHILE

-- The WHILE Flow Element
DECLARE @i AS INT = 1;
WHILE @i <= 10
BEGIN
  PRINT @i;
  SET @i = @i + 1;
END;
GO

BREAK

-- BREAK
DECLARE @i AS INT = 1;
WHILE @i <= 10
BEGIN
  IF @i = 6 BREAK;
  PRINT @i;
  SET @i = @i + 1;
END;
GO

CONTINUE

-- CONTINUE
DECLARE @i AS INT = 0;
WHILE @i < 10
BEGIN
  SET @i = @i + 1;
  IF @i = 6 CONTINUE;
  PRINT @i;
END;
GO

An Example of Using IF and WHILE

-- An Example of Using IF and WHILE
SET NOCOUNT ON;
IF OBJECT_ID('dbo.Numbers', 'U') IS NOT NULL DROP TABLE dbo.Numbers;
CREATE TABLE dbo.Numbers(n INT NOT NULL PRIMARY KEY);
GO

DECLARE @i AS INT = 1;
WHILE @i <= 1000
BEGIN
  INSERT INTO dbo.Numbers(n) VALUES(@i);
  SET @i = @i + 1;
END
GO

 游标

-- Example: Running Aggregations
SET NOCOUNT ON;

DECLARE @Result TABLE
(
  custid     INT,
  ordermonth DATETIME,
  qty        INT, 
  runqty     INT,
  PRIMARY KEY(custid, ordermonth)
);

DECLARE
  @custid     AS INT,
  @prvcustid  AS INT,
  @ordermonth DATETIME,
  @qty        AS INT,
  @runqty     AS INT;

DECLARE C CURSOR FAST_FORWARD /* read only, forward only */ FOR
  SELECT custid, ordermonth, qty
  FROM Sales.CustOrders
  ORDER BY custid, ordermonth;

OPEN C;

FETCH NEXT FROM C INTO @custid, @ordermonth, @qty;

SELECT @prvcustid = @custid, @runqty = 0;

WHILE @@FETCH_STATUS = 0
BEGIN
  IF @custid <> @prvcustid
    SELECT @prvcustid = @custid, @runqty = 0;

  SET @runqty = @runqty + @qty;

  INSERT INTO @Result VALUES(@custid, @ordermonth, @qty, @runqty);
  
  FETCH NEXT FROM C INTO @custid, @ordermonth, @qty;
END

CLOSE C;

DEALLOCATE C;

SELECT 
  custid,
  CONVERT(VARCHAR(7), ordermonth, 121) AS ordermonth,
  qty,
  runqty
FROM @Result
ORDER BY custid, ordermonth;
GO

2012支持的增强开窗函数

SELECT custid, ordermonth, qty,
  SUM(qty) OVER(PARTITION BY custid
                ORDER BY ordermonth
                ROWS UNBOUNDED PRECEDING) AS runqty
FROM Sales.CustOrders
ORDER BY custid, ordermonth;