Microsoft SQL Server 2008 R2 Unleashed- P167 pdf

Now, if you run another update but only specify a value for Weightin the XML string, the Colorcolumn is set to NULL: Update Product_sparse set ProductInfo = ‘.10’ where productID = 5 SEL

Now, if you run another update but only specify a value for Weightin the XML string, the

Colorcolumn is set to NULL:

Update Product_sparse

set ProductInfo = ‘<Weight>.10</Weight>’

where productID = 5

SELECT productID, productName, Color, Weight, SEllEndDate

FROM Product_sparse

where productID = 5

go

productID productName Color Weight SEllEndDate

- -

-5 ValveStem NULL 0.10 NULL

However, if you reference the sparse columns explicitly in an UPDATEstatement, the other

values remain unchanged:

Update Product_sparse

set Color = ‘silver’

where ProductID = 5

SELECT productID, productName, Color, Weight, SEllEndDate

FROM Product_sparse

where productID = 5

go

productID productName Color Weight SEllEndDate

- -

-5 ValveStem silver 0.10 NULL

Column sets are most useful when you have many sparse columns in a table (for example,

hundreds) and operating on them individually is cumbersome Your client applications

may more easily and efficiently generate the appropriate XML string to populate the

column set rather than your having to build an UPDATEstatement dynamically to

deter-mine which of the sparse columns need to be included in the SETclause Applications

might actually see some performance improvement when they select, insert, or update

data by using column sets on tables that have lots of columns

Sparse Columns: Good or Bad?

There is some disagreement in the SQL Server community whether or not sparse columns

are appropriate A number of professionals are of the opinion that any table design that

requires sparse columns is a bad design that does not follow good relational design

guide-lines Sparse columns, by their nature, are heavily denormalized On the other hand,

many times you have to live in the real world and make the best of a bad database design

that you’ve inherited Sparse columns can help solve performance and storage issues in

databases that may have been poorly designed

Although sparse columns can solve certain kinds of problems with database design, you

should never use them as an alternative to proper database and table design As cool as

sparse columns are, they aren’t appropriate for every scenario, particularly when you’re

tempted to violate normalization rules to be able to cram more fields into a table

Spatial Data Types

SQL Server’s support of SQLCLR allows for very rich user-defined types to be utilized For

example, a developer could create a single object that contains multiple properties and

can also perform calculations internally (methods), yet still store it in a single column in a

single row in a database table This allows multiple complex types of data to be stored and

queried in the database, instead of just strings and numbers

SQL Server 2008 makes use of SQLCLR to support two new NET CLR data types for

storing spatial data: GEOMETRYandGEOGRAPHY These types support methods and properties

that allow for the creation, comparison, analysis, and retrieval of spatial data Spatial data

types provide a comprehensive, high-performance, and extensible data storage solution for

spatial data, enabling organizations of any scale to integrate geospatial features into their

applications and services

TheGEOMETRYdata type is a NET CLR data type that supports the planar model/data,

which assumes a flat projection and is therefore sometimes called flat earth Geometry

data represents information in a uniform two-dimensional plane as points, lines, and

polygons on a flat surface, such as maps and interior floor plans where the curvature of

the earth does not need to be taken into account For example, perhaps your user-defined

coordinate space is being used to represent a warehouse facility Within that coordinate

space, you can use theGEOMETRYdata type to define areas that represent storage bays

within the warehouse You can then store data in your database that tracks which

inven-tory is located in which area You could then query the data to determine which forklift

driver is closest to a certain type of item, for example

TheGEOGRAPHYdata type provides a storage structure for geodetic data, sometimes referred

to as round-earth data because it assumes a roughly spherical model of the world It

provides a storage structure for spatial data that is defined by latitude and longitude

coor-dinates using an industry standard ellipsoid such as WGS84, the projection method used

by Global Positioning System (GPS) applications The SQL Server GEOGRAPHYdata type uses

latitude and longitude angles to identify points on the earth Latitude measures how far

north (or south) of the equator a point is, while longitude measures how far east (or west)

of a prime meridian a point is Note that this coordinate system can be used to identify

points on any spherical object, be it a baseball, the earth, or even the moon

TheGEOMETRYandGEOGRAPHYdata types support seven instance types that you can create

and work with in a database:

POINT —A POINTis an exact location and is defined in terms of an X and Y pair of

coordinates, as well as optionally by Z (elevation) and M (measure) coordinates It

does not have a length or any area associated with it These instance types are used

as the fundamental building blocks of more complex spatial types

MULTIPOINT —A MULTIPOINTis a collection of zero or more points

LINESTRING —A LINESTRINGis the path between a sequence of points (that is, a series

of connected line segments) It is considered simple if it does not cross over itself and

is considered a ring if the starting point is the same as the ending point A

LINESTRINGis always considered to be a one-dimensional object; it has length but

does not have area (even if it is a ring)

MULTILINESTRING —A MULTILINESTRINGis a collection of zero or more GEOMETRYor

GEOGRAPHY LINESTRINGinstances

POLYGON —A POLYGONis a closed two-dimensional shape defined by a ring It has both

length and area and has at least three distinct points A POLYGONmay also have holes

in its interior (a hole is defined by another POLYGON) Area within a hole is

consid-ered to be exterior to the POLYGONitself

MULTIPOLYGON —A MULTIPOLYGONinstance is a collection of zero or more POLYGON

instances

GEOMETRYCOLLECTION —A GEOMETRYCOLLECTIONis a collection of zero or more

GEOMETRYorGEOGRAPHYinstances A GEOMETRYCOLLECTIONcan be empty This is

simi-lar to a list or an array in most programming languages The most generic type of

collection is the GEOMCOLLECTION, whose members can be of any type

Representing Spatial Data

The Open Geospatial Consortium, Inc (OGC) is a nonprofit, international, voluntary

consensus standards organization that is leading the development of standards for

geospatial and location-based services The OGC defines different ways to represent

geospatial information as bytes of data that can then be interpreted by theGEOMETRYor

GEOGRAPHYtypes as beingPOINTS,LINESTRINGS, and so on SQL Server 2008 supports three

such formats:

Well-Known Text (WKT)

Well-Known Binary (WKB)

Geography Markup Language (GML)

For the purposes of this chapter, we stick to WKT examples because they are both concise

and somewhat readable The syntax of WKT is not too difficult to understand, so let’s look

at some examples:

POINT(10 100)—Here, 10 and 100 represent X and Y values of the point

POINT(10 100 10 1)—This example shows Z and M values in addition to X and Y

LINESTRING(0 0, 10 100)—The first two values represent the starting point, and

the last two values represent the end point of the line

POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))—Each pair of numbers represents a

point on the edge of the polygon Note that the end point is the same as the starting

point

Working with Geometry Data

As mentioned previously, the geometrydata type is implemented as a common language

runtime (CLR) data type in SQL Server and is used to represent data in a Euclidean (flat)

coordinate system The GEOMETRYtype is predefined and available in each database Any

variable, parameter, or table column can be declared with the GEOMETRYdata type, and you

can operate on geometry data in the same manner as you would use other CLR types

using the built-in methods to create, validate, and query geometry data

NOTE

SQL Server provides a number of methods for theGEOMETRYandGEOGRAPHYdata types

Covering all the available methods is beyond the scope of this chapter The examples

provided here touch on some of the more common methods For more information on

otherGEOMETRYandGEOGRAPHYmethods, refer to SQL Server 2008 Books Online

To assign a value to a column or variable of typeGEOMETRY, you must use one of the

static methods to parse the representation of the data into the spatial data type For

example, to parse geometry data provided in a valid WKT syntax, you can use the

STGeomFromTextmethod:

Declare @geom GEOMETRY

Declare @geom2 GEOMETRY

SET @geom = geometry::STGeomFromText(‘LINESTRING (100 100, 20 180, 180 180)’, 0)

SET @geom2 = geometry::STGeomFromText

(‘POLYGON ((0 0, 150 0, 150 150, 0 150, 0 0))’, 0)

NOTE

The last parameter passed to the method is the spatial reference ID (SRID) parameter

The SRID is required SQL Server 2008 does not perform calculations on pieces of

spatial information that belong to separate spatial reference systems (for example, if

one system uses centimeters and another uses miles, SQL Server simply does not

have the means to automatically convert units) For the GEOMETRYtype, the default

SRID value is 0 The default SRID for GEOGRAPHYis 4326, which maps to the WGS 84

spatial reference system

If you are declaring a LINESTRINGspecifically, you can use the STLineFromTextstatic

method that accepts only valid LINESTRINGs as input:

Declare @geom GEOMETRY

SET @geom = geometry::STLineFromText(‘LINESTRING (100 100, 20 180, 180 180)’, 0)

TheGEOMETRYtype, like other SQLCLR UDTs, supports implicit conversion to and from a

string The string format supported by the GEOMETRYtype for implicit conversion is WKT

Due to this feature, all the following SETstatements are functionally equivalent (the last

twoSETstatements use an implicit SRID of 0):

DECLARE @geom GEOMETRY

SET @geom = geometry::STLineFromText(‘LINESTRING (100 100, 20 180, 180 180)’, 0)

set @geom = Geometry::Parse(‘LINESTRING (100 100, 20 180, 180 180)’)

set @geom = ‘LINESTRING (100 100, 20 180, 180 180)’

After defining a GEOMETRYinstance, you can use the CLR UDT dot notation to access other

properties and methods of the GEOGRAPHYinstance For example, the following code uses

theSTLength()method to return the length of the LINESTRING:

DECLARE @geom GEOMETRY

SET @geom = geometry::STLineFromText(‘LINESTRING (100 100, 20 180, 180 180)’, 0)

select @geom.STLength() as “Length”

go

Length

-273.137084989848

The following example uses the STIntersection()method to return the points where two

GEOMETRYinstances intersect:

DECLARE @geom1 GEOMETRY;

DECLARE @geom2 GEOMETRY;

DECLARE @result GEOMETRY;

SET @geom1 = geometry::STGeomFromText(‘LINESTRING (100 100, 20 180, 180 180)’, 0)

SET @geom2 = geometry::STGeomFromText(‘POLYGON ((0 0, 150 0, 150 150, 0 150, 0

0))’, 0)

SELECT @result = @geom1.STIntersection(@geom2);

SELECT @result.STAsText();

go

-LINESTRING (50 150, 100 100)

All the preceding examples use local variables in a batch You also can declare columns in

a table with the GEOMETRYtype, and you can use the instance properties and methods

against the columns as well:

CREATE TABLE #geom_demo

(

GeomID INT IDENTITY NOT NULL,

GeomCol GEOMETRY

)

INSERT INTO #geom_demo (GeomCol)

VALUES (‘LINESTRING (100 100, 20 180, 180 180)’),

(‘POLYGON ((0 0, 150 0, 150 150, 0 150, 0 0))’),

(‘POINT(10 10)’)

SELECT

GeomID,

GeomCol.ToString() AS WKT,

GeomCol.STLength() AS LENGTH,

GeomCol.STArea() as Area

FROM #geom_demo

drop table #geom_demo

go

GeomID WKT LENGTH Area

- -

-1 LINESTRING ( -100 -100, 20 -180, -180 -180) 273. -137084989848 0

2 POLYGON ((0 0, 150 0, 150 150, 0 150, 0 0)) 600 22500

3 POINT (10 10) 0 0

Working with Geography Data

TheGEOGRAPHYdata type is also implemented as a NET common language runtime data

type in SQL Server Unlike the GEOMETRYdata type in which locations are defined in terms

of X and Y coordinates that can conceivably extend to infinity, the GEOGRAPHYtype

repre-sents data in a round-earth coordinate system Whereas flat models do not “wrap around,”

the round-earth coordinate system does wrap around such that if you start at a point on

the globe and continue in one direction, you eventually return to the starting point

Because defining points on a ball using X and Y is not very practical, the GEOGRAPHYdata

type instead defines points using angles The SQL Server GEOGRAPHYdata type stores

ellip-soidal (round-earth) data as GPS latitude and longitude coordinates Longitude represents

the horizontal angle and ranges from -180 degrees to 180 degrees, and latitude represents

the vertical angle and ranges from -90 degrees to 90 degrees

TheGEOGRAPHYdata type provides similar built-in methods as the GEOMETRYdata type that

you can use to create, validate, and query geography instances

To assign a value to a geography column or variable, you can use the STGeogFromText

methods to parse the parse geometry data provided in a valid WKT syntax into a valid

geography value:

Declare @geog GEOGRAPHY

Declare @geog2 GEOGRAPHY

SET @geog =

geography::STGeomFromText(‘LINESTRING(-122.360 47.656,

-122.343 47.656)’, 4326) SET @geog2 =

geography::STGeomFromText(‘POLYGON((-122.358 47.653,

-122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))’, 4326)

As with the GEOMETRYdata type, you can also use the STLineFromTextstatic method that

accepts only valid LINESTRINGSas input, or you can take advantage of the support for

implicit conversion of WKT strings:

DECLARE @geog GEOGRAPHY

SET @geog = Geography::STLineFromText(‘LINESTRING (-122.360 47.656,

-122.343 47.656)’, 4326) set @geog = Geography::Parse(‘LINESTRING (-122.360 47.656,

-122.343 47.656)’) set @geog = ‘LINESTRING (-122.360 47.656, -122.343 47.656)’

The following code uses the STLength()andSTArea()methods to return the length of the

LINESTRING:

DECLARE @geom GEOMETRY

SET @geom = geometry::STLineFromText(‘LINESTRING (100 100, 20 180, 180 180)’, 0)

select @geom.STLength() as “Length”

go

Length

-273.137084989848

The preceding examples use local variables in a batch You also can declare columns in a

table using the geographydata type, and you can use the instance properties and methods

against the columns as well:

CREATE TABLE #geog

( id int IDENTITY (1,1),

GeogCol1 GEOGRAPHY,

GeogCol2 AS GeogCol1.STAsText() );

GO

INSERT INTO #geog (GeogCol1)

VALUES (geography::STGeomFromText

(‘LINESTRING(-122.360 47.656, -122.343 47.656)’, 4326));

INSERT INTO #geog (GeogCol1)

VALUES (geography::STGeomFromText

(‘POLYGON((-122.358 47.653,

-122.348 47.649, -122.348 47.658, -122.358 47.658, -122.358 47.653))’, 4326));

GO

DECLARE @geog1 GEOGRAPHY;

DECLARE @geog2 GEOGRAPHY;

DECLARE @result GEOGRAPHY;

SELECT @geog1 = GeogCol1 FROM #geog WHERE id = 1;

SELECT @geog2 = GeogCol1 FROM #geog WHERE id = 2;

SELECT @result = @geog1.STIntersection(@geog2);

SELECT Intersection = @result.STAsText();

go

Intersection

-

-LINESTRING (-122.3479999999668 47.656000260658459

, -122.35799999998773 47.656000130309728)

Spatial Data Support in SSMS

When querying spatial data in SSMS, you’ll find that SSMS has a built-in capability to plot

and display some basic maps of your spatial data

To demonstrate this, you can run the following query in the AdventureWorks2008R2or

AdventureWorks2008database in SSMS:

select SpatialLocation

from person.Address a

inner join

person.StateProvince sp

on a.StateProvinceID = sp.StateProvinceID

and sp.CountryRegionCode = ‘US’

After the query runs, you should see a Spatial Results tab next to the Results tab (see

Figure 42.3) Click on this tab, and the location points are plotted on a map Select the

Bonne Projection If you look closely, you can see that the geographical points plotted

roughly provide an outline of the United States If you mouse over one of the points,

SSMS displays the associated address information displayed in the Person.Addresstable

In addition to displaying maps of geography data values, SSMS can also display geometry

data, showing lines, points, and polygons in an X-Y grid For example, if you run the

following query and click on the Spatial Results tab, it should display a box like the one

shown in Figure 42.4:

declare @smallBox GEOMETRY = ‘polygon((0 0, 0 2, 2 2, 2 0, 0 0))’;

select @smallbox

If you want to display multiple polygons, points, or lines together at the same time, they

have to be returned as multiple rows in a single table If you return them as multiple

columns, SSMS displays only one column at a time in the Spatial Results tab For example,

if you run the following query, SSMS displays two boxes, the polygon defined by the

inter-section of the two boxes, as well as the overlapping line defined by the LineString, as

shown in Figure 42.5:

FIGURE 42.3 Displaying a map of Person.Address records in SSMS

FIGURE 42.4 Displaying a polygon in SSMS

FIGURE 42.5 Displaying intersecting polygons and an overlapping Line in SSMS