TSQL update 简单应用小总结

UPDATE 有两种基本的格式。一种是用静态数据来修改表，另一种是用其他表中的数据来修改表。下面是第一种格式：

 UPDATE #famousjaycees
    SET jc = 'Jhony cash',
        occupation = 'singer/songwrite',
        becamefamous = 1955,
        notes = 'began c'
  WHERE jc = 'Jhony caeer'

第二种格式如下：

 IF NOT EXISTS
       (SELECT *
          FROM sys.sysobjects
         WHERE [name] = 'semifamousjaycees')
    CREATE TABLE semifamousjaycees
    (
       jc             VARCHAR (15),
       occupation     VARCHAR (25),
       becamefamous   INT DEFAULT 0,
       notes          TEXT NULL
    )
 
 UPDATE f
    SET jc = s.jc,
        occupations = s.occupations,
        becamefamous = s.becamefamous,
        notes = s.notes
   FROM famousejaycees f
        JOIN semifamousjaycee ON (f.becamesou = s.becamefouse)

UPDATE 的另外一种用途：使用update 检测约束。

如果使用 bulk insert 或者其他大批量的载入工具来对有insett 触发器的表进行追加数据，你们你会发现触发器不能触发。而且，即使bulk insert 不妨碍约束，也会是操作变的非常的慢。如果在载入数据时忽略约束，那么就快的多了。所以，比较的好的方法是，载入数据结束后，马上在对表一个假的update 操作。这个假的修改操作只是简单地将列值为其身的值。这样就会触发触发器约束进行检测。如果其中有包含错数数据的行，那么update失败.例如：

 IF NOT EXISTS
       (SELECT *
          FROM sys.sysobjects
         WHERE [name] = 'famousejaycees')
    CREATE TABLE famousejaycees
    (
       jc             VARCHAR (15) CHECK (left (jc, 3) <> 'Joe'), -- establish a check constraint
       occupation     VARCHAR (25),
       becamefamous   INT DEFAULT 0,
       notes          TEXT NULL
    )
 go
 
 BULK INSERT famousejaycees
        FROM 'C:\famous.bcp'
        WITH (FIELDTERMINATOR = '|', ROWTERMINATOR = '\r\n')
 
 --check that the miscreant is in place
 SELECT * FROM famousejaycees
 
 --now do the faux update
 
 update famousejaycees
 set jc=jc, occupation = occupation, becamefamous = becamefamous, notes = notes

使用update 交换行列：

IF NOT EXISTS
      (SELECT *
         FROM sys.sysobjects
        WHERE [name] = 'sample')
   CREATE TABLE sample
   (
      k1      INT IDENTITY,
      samp1   FLOAT DEFAULT (rand () * 1000),
      samp2   FLOAT DEFAULT (rand () * 1000)
   )
 
SELECT * FROM sample;
 
DECLARE @swap   FLOAT
 
UPDATE sample
   SET @swap = samp1, samp1 = samp2, samp2 = @swap