數據庫中每一行到底占用多少空間，在這里，做個小測試~~~這里只做了堆表的計算，如果包含索引，按照文檔把索引的列也加上就OK啦~

建個測試表，然后用DBCC PAGE打印出Slot的信息

CREATE TABLE TstA( col1 CHAR(5) NULL, col2 CHAR(5) NULL, col3 VARCHAR(5) NULL, col4 VARCHAR(10) NULL, col5 VARCHAR(50) NULL)INSERT INTO TstA (col1,col2,col3,col4,col5) VALUES ('aa1','2222222222','joan2','aoaonfoen','1111111')dbcc ind(TestDB, Object_id('TstA'),-1) 

DBCC PAGE(TestDB,1,11957,1)

然后我就直接把slot的消息貼出來分析吧~~

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

Slot 0, Offset 0x60, Length 51, DumpStyle BYTE

Record Type = PRIMARY_RECORD Record Attributes = NULL_BITMAP VARIABLE_COLUMNS

Record Size = 51

Memory Dump @0x0A93C060

00000000: 30000e00 61613120 206a6f61 6e320500 †0...aa1 joan2..

00000010: 00030023 002c0033 00323232 32323232 †...#.,.3.2222222

00000020: 32323261 6f616f6e 666f656e 31313131 †222aoaonfoen1111

00000030: 313131†††††††††††††††††††††††††††††††111

4 8 12 16 20 24 28 32 36 40 44 48 52

30000e0061613120 206a6f61 6e32050000030023 002c0033 00323232 323232332323261 6f616f6e 666f656e31313131313131

1 2 3 4 5 6 7 8 9

1： 固定長度列結束位置

2： 固定長度第一列(col1)

3： 固定長度第二列(col3) --如果之后還有更多的列，繼續往后排

4： 行包含的欄位總數，本例為5

5： 空值維護：計算方式為 2+ (可為空列數+7)/8

6： 每一個可變列的結束位置。長度計算 2 + (可變列列數*2)

7+：變長列的每一個填充列

驗證了這一句話，每行的開銷

• ix bytes per row for status information and length information.
• One bit per fixed width column, rounding up to the nearest byte.
• If there are any variable length columns - four bytes for the first, plus two bytes for each additional variable length column
• An additional two bytes per row for the offset pointer located at the end of the page.

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

經過測試，無論列的順序怎么排，首先會先把定長的字段先排出來，然后再排變長字段~好吧~測試結束

小弟不才~歡迎大家指出不足

參考：

　　http://technet.microsoft.com/zh-cn/library/ms189124.aspx

PS：上面2個DBCC 的語法

dbcc page ( {'dbname' | dbid}, filenum, pagenum [, printopt={0|1|2|3} ])

The filenum and pagenum parameters are taken from the page IDs that come from various system tables and appear in DBCC or other system error messages. A page ID of, say, (1:354) has filenum = 1 and pagenum = 354.

The printopt parameter has the following meanings:

0 - print just the page header1 - page header plus per-row hex dumps and a dump of the page slot array (unless its a page that doesn't have one, like allocation bitmaps)2 - page header plus whole page hex dump3 - page header plus detailed per-row interpretation