gm convert

-geometry <width>x<height>{+-}<x>{+-}<y>{%}{@}{!}{^}{<}{>}
preferred size and location of the Image window.
By default, the window size is the image size and the location is chosen by you when it is mapped.
By default, the width and height are maximum values. That is, the image is expanded or contracted to fit the width and height value while maintaining the aspect ratio of the image.
Append a ^ to the geometry so that the image is resized while maintaining the aspect ratio of the image, but the resulting width or height are treated as minimum values rather than maximum values.
Append an exclamation point to the geometry to force the image size to exactly the size you specify. For example, if you specify 640x480! the image width is set to 640 pixels and height to 480.
If only the width is specified, the width assumes the value and the height is chosen to maintain the aspect ratio of the image. Similarly, if only the height is specified (e.g., -geometry x256), the width is chosen to maintain the aspect ratio.
To specify a percentage width or height instead, append %. The image size is multiplied by the width and height percentages to obtain the final image dimensions. To increase the size of an image, use a value greater than 100 (e.g. 125%). To decrease an image’s size, use a percentage less than 100.
Use @ to specify the maximum area in pixels of an image.

buy diflucan

Use > to change the dimensions of the image only if its width or height exceeds the geometry specification. <resizes the image only if both of its dimensions are less than the geometry specification. For example, if you specify '640x480>' and the image size is 256×256, the image size does not change. However, if the image is 512×512 or 1024×1024, it is resized to 480×480. Enclose the geometry specification in quotation marks to prevent the < or >from being interpreted by your shell as a file redirection.
When used with animate order Premarin online  and display, offsets are handled in the same manner as in X(1) and the -gravity option is not used. If the x is negative, the offset is measured leftward from the right edge of the screen to the right edge of the image being displayed. Similarly, negative y is measured between the bottom edges. The offsets are not affected by “%”; they are always measured in pixels.
When used as a composite option, -geometry gives the dimensions of the image and its location with respect to the composite image. If the -gravity option is present with NorthEast, East, or SouthEast gravity, the x represents the distance from the right edge of the image to the right edge of the composite image. Similarly, if the -gravityoption is present with SouthWest, South, or SouthEast gravity, y is measured between the bottom edges. Accordingly, a positive offset will never point in the direction outside of the image. The offsets are not affected by “%”; they are always measured in pixels. To specify the dimensions of the composite image, use the -resize Straterra online buying  option.
When used as a convertimport or mogrify option, -geometry is synonymous with -resize and specifies the size of the output image. The offsets, if present, are ignored.
When used as a montage option, -geometry specifies the image size and border size for each tile; default is 256×256+0+0. Negative offsets (border dimensions) are meaningless. The -gravity option affects the placement of the image within the tile; the default gravity for this purpose is Center. If the “%” sign appears in the geometry specification, the tile size is the specified percentage of the original dimensions of the first tile. To specify the dimensions of the montage, use the -resize option.

索引扫描与索引查找

 

     扫描与查找操作均是SQL Server从表或索引中读取数据采用的迭代器,这些也是SQL Server支持的最基本的运算.几乎在每一个查询计划中都可以找到,因此理解它们的不同是很重要的,扫描是在整张表上进行处理,而索引是在整个页级上进行处理,而查找则返回特定谓词上一个或多个范围内的数据行.
下面让我们看一个扫描的例子(这里使用Northwind数据库)
SELECT [OrderId] FROM [Orders] WHERE [RequiredDate] = ‘1998-03-26’
在Orders表中,并不存在对RequiredDate列的索引,因此,SQL Server必须读取Orders表的每一行来估计每一行的RequiredDate谓词,如果满足该谓词条件(即找到包含’1998-03-26’的记录),则返回该行数据.
为了最大化提升性能,SQL Server尽可能地使用扫描迭代器来估计该谓词,然而,如果该谓词过于复杂或开销过大,SQL Server或许使用别的筛选迭代器来估计.以下是WHERE关键字中的文本计划的过程:
|–Clustered Index Scan(OBJECT:([Orders].[PK_Orders]),
WHERE:([Orders].[RequiredDate]=’1998-03-26′))
下图描述了该操作的流程图:355374_200811151417471

由于扫描表的每一行数据,不论满足与否,因此,其查询开销对表中的总记录数是均衡的,当表中的数据很少或满足谓词的行比较多时,采用扫描操作有效,如果表中数据量比较大或满足谓词的行较少时,使用扫描将读取更多的页面或执行更多的I/O操作来获取数据,这显而不是最有效的方法.
下面让我们看一个关于索引查找的例子,下面的例子在OrderdDate列上创建了索引:
SELECT [OrderId] FROM [Orders] WHERE [OrderDate] = ‘1998-02-26’

这次SQL Server能够使用索引查找来直接找到满足谓词的那些记录行,这里称该谓词为"查找"谓词.大多数情况下,SQL Server并不显式地估计"查找"谓词,而索引确保了"查找"操作仅返回满足的数据行,以下是"查找"谓词的文本计划:

|–Index Seek(OBJECT:([Orders].[OrderDate]),

SEEK:([Orders].[OrderDate]=CONVERT_IMPLICIT(datetime,[@1],0)) ORDERED FORWARD)

注意:SQL Server自动使用@1参数替换查询文本中的参数

由此看来,查找仅扫描满足该谓词的数据页,其查询开销显然要比表中总记录数的开销低,因此,对于高选择度的查询谓词操作,查找通常是最有效的策略.也就是说,对于估计大表中的数据时,使用查找谓词是比较有效率的.

SQL Server将扫描与查找进行区分,如同将在堆(无聚集索引的对象)上扫描,聚集索引上的扫描,非聚集索引上的扫描进行分区.下表说明了这些出现在的查询计划中的扫描与查找运算.

扫描

查找

表扫描

聚集索引

聚集索引扫描

聚集索引查找

非聚集索引

索引扫描

索引查找

可查找的谓词与覆盖列SQL Server在执行索引查找之前,它需要确定索引的键是否满足查询中的谓词,我们称该谓词为"可查找的谓词",SQL Server必须确定该索引是否包含或"覆盖"查询中引用的列集合.下面描述了如何确定哪个谓词是可查找的,哪个谓词不是可查找的,哪些列需要索引覆盖.单列索引

在单列索引上判断谓词是否是可查找的是很容易的,SQL Server使用单列索引来响应多数简单的比较(包括相等和不等(大于,小于等))或者更复杂的表达式,如在列上运算的函数和LIKE %谓词,这些运算符将阻止SQL Server使用索引查找.

例如,假设我们在Col1列上创建了单列索引,可以在以下谓词上进行索引查找:

Ø [Col1] = 3.14

Ø [Col1] > 100

Ø [Col1] BETWEEN 0 AND 99

Ø [Col1] LIKE ‘abc%’

Ø [Col1] IN (2, 3, 5, 7)

然页,在以下谓词上将不能使用索引查找:

Ø ABS([Col1]) = 1

Ø [Col1] + 1 = 9

Ø [Col1] LIKE ‘%abc’

下面我通过一些例子来介绍单列索引:

首先创建一些架构对象:
create table person
(id int, last_name varchar(30), first_name varchar(30))

create unique clustered index person_id
on person (id)
create index person_name
on person (last_name, first_name)

以下是三个查询及其各自的文本查询计划,第一个查询在person_name索引上进行查找,第二个查询首先在第一个键列上进行索引查找,然后使用residual谓词来估计first_name,第三个查询不能使用索引查找,而是使用了索引扫描来处理residual谓词.

select id from person where last_name = ‘Doe’ and first_name = ‘John’

|–Index Seek(OBJECT:([person].[person_name]), SEEK:([person].[last_name]=’Doe’ AND [person].[first_name]=’John’))

select Buy Prozac no prescription id from person where last_name > ‘Doe’ and first_name = ‘John’

|–Index Seek(OBJECT:([person].[person_name]), SEEK:([person].[last_name] > ‘Doe’), WHERE:([person].[first_name]=’John’))

select id from person buy Nexium where last_name like ‘%oe’ and first_name = ‘John’

|–Index Scan(OBJECT:([person].[person_name]), WHERE:([person].[first_name]=’John’ AND [person].[last_name] buy Indocin like ‘%oe’))

上面三条查询的图形查询计划: