Microsoft SQL Server 2008 R2 Unleashed- P174 pot

Panteley Sylvia 100 White Johnson 100 Straight Dean 100 Locksley Charlene 100 Carson Cheryl 100 Blotchet-Halls Reginald 100 del Castillo Innes 100 Note that no real difference exists bet

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Panteley Sylvia 100

White Johnson 100

Straight Dean 100

Locksley Charlene 100

Carson Cheryl 100

Blotchet-Halls Reginald 100

del Castillo Innes 100

Note that no real difference exists between left and right outer joins except for specifying which table on which side of the join condition is to be the controlling, or outer, table For example, the previous query would provide the same result if you reversed the tables in the join clause and made it a right outer join: select au_lname, au_fname, avg(royaltyper) from dbo.titleauthor ta right outer join dbo.authors a on ta.au_id = a.au_id group by au_lname, au_fname order by 3 A full outer join returns all matching rows from both tables, along with all rows from each table, without a corresponding match in the other table: select a.au_fname, p.pub_name from dbo.authors a full outer join dbo.publishers p on a.state = p.state go au_fname pub_name -

-James A NULL Francine du Plessix Kumquat Technical Publishing Jean NULL E.L Nordome Titles Justin Algodata Infosystems April Sidney’s Books and More Ron Algodata Infosystems Jack NULL Matt NULL Josef NULL

Albert Ramona Publishers

NULL Gooseberry Titles

NULL Binnet & Hardley

NULL GGG&G

NULL Lucerne Publishing

NULL Tomato Books

NULL Significant Titles Company

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OUTER JOIN Versus WHERE Clause Matching

With the ANSI join syntax, you specify the join condition in the FROMclause Additional

search conditions can be specified in either the JOINclause or WHEREclause It’s important

to remember that in a left or right outer join, search conditions specified in the ONclause

work differently than search conditions in the WHEREclause:

Search conditions in the WHEREclause always exclude nonmatching rows.

Search conditions in the ONclause sometimes exclude rows and sometimes do not.

Needless to say, it can be somewhat confusing to figure out which rows and data values

will be returned To demonstrate the use of search conditions in the WHEREclause versus

theONclause, the examples presented in this section make use of the two views shown in

Listing 43.15.

LISTING 43.15 CREATE VIEW Statements for Outer Join Examples

CREATE VIEW dbo.STORES_V1 AS

SELECT STOR_ID, CITY FROM DBO.STORES WHERE STOR_ID BETWEEN ‘A001’ AND ‘A005’

go

CREATE VIEW dbo.STORES_V2 AS

SELECT STOR_ID, STATE FROM DBO.STORES WHERE STOR_ID BETWEEN ‘A002’ AND ‘A007’

UNION ALL

SELECT ‘A004’, ‘MA’

go

select * from dbo.stores_v1

select * from dbo.stores_v2

STOR_ID CITY

-

-A001 Dublin

A002 Oakland

A003 Bisbee

A004 White Plains

A005 Thomaston

(5 row(s) affected)

STOR_ID STATE

-A002 NJ

A003 AZ

A004 NY

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A005 GA

A006 CA

A007 CA

A004 MA

Listing 43.16 provides an example of a left outer join query that includes the search

condition in the ONclause All rows are returned from STORES_V1, and NULLvalues are

returned for STORES_V2where there isn’t a matching STOR_IDor where there is a matching

STOR_IDbutSTATEis not equal to ’GA’.

LISTING 43.16 Specifying the Search Condition in the ON Clause

SELECT * FROM DBO.STORES_V1 V1

LEFT OUTER JOIN DBO.STORES_V2 V2

ON V1.STOR_ID = V2.STOR_ID

AND V2.STATE <> ‘GA’

ORDER BY V1.STOR_ID ,V2.STATE

go

STOR_ID CITY STOR_ID STATE

-A001 Dublin NULL NULL

A002 Oakland A002 NJ

A003 Bisbee A003 AZ

A004 White Plains A004 MA

A004 White Plains A004 NY

A005 Thomaston NULL NULL

Now, if you put the search condition in the WHEREclause, as shown in Listing 43.17, the

nonmatching rows from STORES_V2are filtered out because the NULLvalue returned for

STATEdoes not match the WHEREclause search criteria WHERE V2.STATE <> ‘GA’.

(Remember that NULLvalues are neither equal to nor not equal to other values.)

LISTING 43.17 Specifying a Search Condition in a WHERE Clause

WHERE V2.STATE <> ‘GA’

go

-A002 Oakland -A002 NJ

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A003 Bisbee A003 AZ

To include the nonmatching rows from STORES_V2, you need to add a check for NULLto

theWHEREclause, as shown in Listing 43.18.

LISTING 43.18 Including Nonmatching Inner Table Rows That Do Not Match a WHERE Clause

Search Condition

WHERE (V2.STATE <> ‘GA’ or V2.STATE is NULL)

go

A003 Bisbee A003 AZ

Notice that the row whereSTOR_ID = ‘A005’is still not included in the result set The

query shown in Listing 43.18 also demonstrates another difference between specifying a

search condition in theWHEREclause and theONclause In this case, the outer join is

performed first, so that all rows and selected column values are returned from

STORES_V2, including the row whereSTOR_ID = ‘A005’, without considering theWHERE

clause condition:

go

A003 Bisbee A003 AZ

A005 Thomaston A005 GA

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After the join result is returned, because the STATEvalue is equal to ’GA’, the search

condi-tion in the WHEREclause (V2.STATE <> ‘GA’) filters out that row.

In a left or right outer join, a search condition in the ONclause also works differently,

depending on whether it refers to a field in the inner or outer table If the ONclause search

condition refers to a field in the outer table, it determines whether the related row finds a

match (The outer row is returned regardless.) For example, Listing 43.19 demonstrates a

search condition in the ONclause that restricts which rows in STORES_V1(the outer table)

join to STORES_V2 The join is performed only for those rows in STORES_V1whereCITYis

greater than N However, all rows from STORES_V1are still returned.

LISTING 43.19 Specifying an ON Clause Search Condition on the Outer Table

AND V1.CITY > ‘N’

go

A003 Bisbee NULL NULL

If theONclause search condition refers to a field in the inner table, it determines

whether the related row matches the join Listing 43.20 shows an example of specifying

theONclause search condition on the inner table Again, notice that all rows from

STORES_V1are returned, but only the matching rows are returned fromSTORES_V2, where

STOR_IDis less thanA004.

LISTING 43.20 Specifying an ON Clause Search Condition on the Inner Table

AND V2.STOR_ID < ‘A004’

go

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A001 Dublin NULL NULL

A003 Bisbee A003 AZ

A004 White Plains NULL NULL

A005 Thomaston NULL NULL

When you perform a left or right outer join, a search condition against the outer table in

theONclause works differently from the same search condition specified in the WHERE

clause As shown in Listing 43.19, when the search condition in the ONclause filters on a

field in the outer table, the outer row is returned, regardless, with no matching rows

returned from the inner table However, if the search condition on the OUTERtable is

spec-ified in the WHEREclause, the outer row is eliminated from the result set, as shown in

Listing 43.21.

LISTING 43.21 Specifying an Outer Table Search Condition in the WHERE Clause

WHERE V1.CITY > ‘N’

go

-A002 Oakland -A002 NJ

Nested Outer Joins

When using the ANSI JOINsyntax, you must be careful about mixing outer joins with

inner joins because the query may not generate the desired result if the outer join is not

continued down to the lowest level For example, consider the query shown in Listing

43.22 The intent of this query is to list all authors whose state equals NEand, for those

authors, display the titles of their associated books, if any.

LISTING 43.22 An Outer Join Nested in an Inner Join

select left(au_lname, 20) as au_lname, au_fname, left(title, 20) as title

from dbo.authors a

left join dbo.titleauthor ta on a.au_id = ta.au_id

join dbo.titles t on ta.title_id = t.title_id

where a.state = ‘NE’

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go

au_lname au_fname title

-Patterson Richard North The Lasko Tangent

Patterson Richard North The Outside Man

Patterson Richard North Private Screening

Patterson Richard North Eyes of a Child

Patterson Richard North Degree of Guilt

Patterson Richard North Escape the Night

However, because the outer join is not carried to the titlestable, the author with no

matching row in the titleauthortable ends up getting filtered from the result set The

reason is that when the outer join is performed between authorsandtitleauthor,

because no matching row is found, NULLis returned for title_id Because a normal inner

join is performed on the titlestable, the NULLvalue for title_iddoes not match any

rows in the titlestable, so the author with no matching rows in titleauthorends up

getting filtered out To see those authors, you need to modify the query in Listing 43.22 to

carry the outer join down to the join between titleauthorandauthors:

select left(au_lname, 20) as au_lname, au_fname, left(title, 20) as title

from dbo.authors a

left join dbo.titleauthor ta on a.au_id = ta.au_id

left join dbo.titles t on ta.title_id = t.title_id

where a.state = ‘NE’

go

au_lname au_fname title

-Patterson Richard North The Lasko Tangent

Patterson Richard North The Outside Man

Patterson Richard North Private Screening

Patterson Richard North Eyes of a Child

Patterson Richard North Degree of Guilt

Patterson Richard North Escape the Night

McBadden Heather NULL

Working with Full Outer Joins

A full outer join selects rows from both tables and joins those rows that match on the join

fields In addition to the matching rows, one copy of each nonmatching row from each

table is returned Listing 43.23 shows an example of a full outer join.

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LISTING 43.23 Full Outer Join Example

FULL OUTER JOIN DBO.STORES_V2 V2

ORDER BY V1.STOR_ID ,V2.STOR_ID ,V2.STATE

go

-NULL -NULL A006 CA

NULL NULL A007 CA

A003 Bisbee A003 AZ

As you can see from the results in Listing 43.23, all rows are returned from both

STORES_V1andSTORES_V2.

In a full outer join, a search condition in theONclause is handled differently from a search

condition in theWHEREclause in that it never results in a row being excluded from the result

set All it does is categorize the input row as being either matching or nonmatching In

Listing 43.24, a search condition (V1.STOR_ID > ‘A003’) is specified in theONclause As you

can see, any rows that do not meet that search condition are returned as nonmatching rows.

LISTING 43.24 Specifying a Search Condition in a Full Outer Join ON Clause

FULL OUTER JOIN DBO.STORES_V2 V2

AND V1.STOR_ID > ‘A003’

go

-NULL -NULL A002 NJ

NULL NULL A003 AZ

NULL NULL A006 CA

NULL NULL A007 CA

A002 Oakland NULL NULL

A003 Bisbee NULL NULL

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As you can see, when you work with full outer joins, search arguments in the ONclause

serve only to define which rows are used as matching rows for a join Search arguments

specified in the WHEREclause define which rows are returned It’s important to note that

theWHEREclause conditions behave as if the join is an inner join and are applied after the

join is done Listing 43.25 shows an example.

LISTING 43.25 Specifying a Search Condition in a Full Outer Join WHERE Clause

SELECT * FROM dbo.STORES_V1 V1

FULL OUTER JOIN dbo.STORES_V2 V2

WHERE V1.STOR_ID > ‘A003’

go

-A004 White Plains -A004 MA

Generating T-SQL Statements with T-SQL

The system catalogs in SQL Server 2008 contain a wealth of information you can use to

save a lot of time and effort when generating SQL statements that need to be run

repeat-edly on a large number of database objects or when trying to build a column list for a

query You can use T-SQL code to select information from the system catalogs, system

tables, and system views to generate SELECTstatements and the like For example, say you

want to grant EXECUTEpermission to the user fredon each stored procedure in the

bigpubs2008database This can be a tedious task to perform using SSMS because in the

Securables dialog for the user fred, you have to select each procedure, one at a time, and

click the Grant Execute check box If there were a large number of procedures, this could

be pretty time-consuming, and your mouse-clicking finger would probably get pretty tired.

The quicker and easier way would be to build the SQL statements necessary to grant

EXECUTEpermission to fredon all the stored procedures The following SELECTstatement

can be used to generate a SQL script with those commands:

select ‘grant execute on ‘ + name + ‘ to fred’

from sys.procedures

order by name

go

-grant execute on byroyalty to fred

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grant execute on cursor_proc to fred

grant execute on error_handler to fred

grant execute on find_books_by_type2 to fred

grant execute on gen_sequence to fred

grant execute on get_authors to fred

grant execute on get_next_item_from_queue to fred

grant execute on get_titles to fred

grant execute on p_explicit_cols to fred

grant execute on p_fetch_explicit_cols to fred

grant execute on p_insert_explicit_cols to fred

grant execute on reptq1 to fred

grant execute on SHOW_PARTS_LIST to fred

grant execute on title_authors to fred

grant execute on trantest to fred

grant execute on ytd_sales to fred

grant execute on ytd_sales2 to fred

You can copy and paste the output from this statement into a query window in SSMS and

execute it to grant the desired permissions When you get to know your system catalog

views, you can begin to automate the generation of a number of SQL operations in this

manner, freeing up your time to spend on more interesting projects.

When you are writing T-SQL code that needs to check for both errors and the number of

rows affected after your SQL statements, one of the common pitfalls is trying to get both

the error status and the number of rows after a SQL statement runs You have to

remem-ber that all SQL statements except the DECLAREstatement reset the value of @@ROWCOUNT

and@@ERRORto the status of the last command executed.

If after a SQL statement you check the value of @@ERROR, the statement used to check

@@ERRORresets@@ROWCOUNT If you check @@ROWCOUNTfirst, it resets the value of @@ERROR To

check both values, you need to use an assignment SELECTimmediately after the SQL

state-ment you are checking and capture both values into local variables Note that you cannot

accomplish this with the SETstatement because the SETstatement allows setting a value

to only a single variable at a time.

The example in Listing 43.26 provides a way to capture and check both @@ROWCOUNTand

@@ERRORafter an UPDATEstatement in a T-SQL batch.

LISTING 43.26 Capturing Both @@ROWCOUNT and @@ERROR After an UPDATE Statement

declare @rowcnt int,

@error int

UPDATE dbo.titles set price = price * 1.10

where type = ‘fiction’

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