barcode generator in vb.net 2005 Multitable Joins in Standard SQL in Software

Make QR Code in Software Multitable Joins in Standard SQL

Multitable Joins in Standard SQL
Scanning Denso QR Bar Code In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Quick Response Code Creator In None
Using Barcode generator for Software Control to generate, create QR Code ISO/IEC18004 image in Software applications.
An important advantage of the standard SQL notation is that it allows very clear specification of three-table or four-table joins. To build these more complex joins, any of the join expressions shown in Figure 7-13 and described in the preceding sections can be enclosed in parentheses. The resulting join expression can itself be used in another join expression, as if it were a simple table. Just as SQL allows you to combine mathematical operations (+, , *, and /) with parentheses and build more complex expressions, the SQL standard allows you to build more complex join expressions in the same way. To illustrate multitable joins, assume that a new PARENTS table has been added to the database containing the GIRLS and BOYS example we have been using. The PARENTS table has three columns:
QR Code 2d Barcode Recognizer In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
Paint QR Code JIS X 0510 In C#
Using Barcode drawer for Visual Studio .NET Control to generate, create QR image in Visual Studio .NET applications.
CHILD TYPE PNAME Matches the NAME column in the GIRLS or BOYS table Specifies FATHER or MOTHER First name of the parent
QR Code Generator In VS .NET
Using Barcode printer for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
Paint Quick Response Code In VS .NET
Using Barcode encoder for .NET Control to generate, create Quick Response Code image in .NET applications.
Full Outer Join Left Outer Join Right Outer Join
QR Code Generation In Visual Basic .NET
Using Barcode encoder for VS .NET Control to generate, create QR image in Visual Studio .NET applications.
Code 3 Of 9 Drawer In None
Using Barcode creator for Software Control to generate, create Code 39 Full ASCII image in Software applications.
PART II
Bar Code Generation In None
Using Barcode drawer for Software Control to generate, create bar code image in Software applications.
Barcode Creation In None
Using Barcode drawer for Software Control to generate, create barcode image in Software applications.
Matched TBL1 rows with NULL values for TBL2 columns
Code 128A Drawer In None
Using Barcode maker for Software Control to generate, create Code128 image in Software applications.
Paint UPC A In None
Using Barcode generation for Software Control to generate, create UPC Code image in Software applications.
Matched TBL1/TBL2 row pairs Inner Join
Painting Leitcode In None
Using Barcode maker for Software Control to generate, create Leitcode image in Software applications.
GS1 RSS Creator In Java
Using Barcode creator for Java Control to generate, create GS1 DataBar Stacked image in Java applications.
Matched TBL2 rows with NULL values for TBL1 columns
Bar Code Creator In Java
Using Barcode creation for Eclipse BIRT Control to generate, create barcode image in BIRT reports applications.
Draw Bar Code In None
Using Barcode printer for Office Excel Control to generate, create barcode image in Microsoft Excel applications.
Unmatched TBL1 rows with NULL values for TBL2 columns
Data Matrix 2d Barcode Creator In Java
Using Barcode encoder for Eclipse BIRT Control to generate, create Data Matrix 2d barcode image in BIRT reports applications.
DataMatrix Recognizer In VB.NET
Using Barcode scanner for .NET Control to read, scan read, scan image in .NET applications.
Unmatched TBL1/TBL2 row pairs Cross Join Union Join
Encode Universal Product Code Version A In Objective-C
Using Barcode generator for iPhone Control to generate, create UCC - 12 image in iPhone applications.
Bar Code Drawer In None
Using Barcode creation for Microsoft Word Control to generate, create barcode image in Word applications.
Unmatched TBL2 rows with NULL values for TBL1 columns
TBL1, NULL-extended (m rows)
All TBL1 TBL2 pairs (m n rows)
TBL2, NULL-extended (n rows)
FIGURE 7-14
Relationships among join types
Part II:
Retrieving Data
A row in the GIRLS or BOYS table can have two matching rows in the PARENTS table, one specifying a MOTHER and one a FATHER, or it can have only one of these rows, or it can have no matching rows if no data on the child s parents is available. The GIRLS, BOYS, and PARENTS tables together provide a rich set of data for some multitable join examples. Suppose you wanted to make a list of all of the girls, along with the names of their mothers and the names of the boys who live in the same city. Here is one query that produces the list:
SELECT FROM ON JOIN ON WHERE GIRLS.NAME, PNAME, BOYS.NAME ((GIRLS JOIN PARENTS PARENTS.CHILD = NAME) BOYS (GIRLS.CITY = BOYS.CITY)) TYPE = 'MOTHER';
Because both of these joins are inner joins, any girl who does not have a boy living in the same city or any girl who does not have a mother in the database will not show up in the query results. This may or may not be the desired result. To include those girls without a matching mother in the database, you would change the join between the GIRLS and the PARENTS table to a left outer join, like this:
SELECT FROM ON JOIN ON WHERE GIRLS.NAME, PNAME, BOYS.NAME ((GIRLS LEFT JOIN PARENTS PARENTS.CHILD = NAME) BOYS (GIRLS.CITY = BOYS.CITY)) (TYPE = 'MOTHER') OR (TYPE IS NULL);
This query will include all of the girl/boy pairs, regardless of whether the girls have a mother in the database, but it will still omit girls who do not live in a city with any of the boys. To include these girls as well, the second join must also be converted to a left outer join:
SELECT FROM ON LEFT ON WHERE GIRLS.NAME, PNAME, BOYS.NAME ((GIRLS LEFT JOIN PARENTS PARENTS.CHILD = NAME) JOIN BOYS (GIRLS.CITY = BOYS.CITY)) (TYPE = 'MOTHER') OR (TYPE IS NULL);
Note that the NULL-extension of the GIRLS rows by the outer join with their mothers also creates some additional complication in the WHERE clause. The girls without matching mothers will generate rows with not only a NULL mother s name (PNAME) column, but also a NULL value in the TYPE column. The simple selection criterion
WHERE (TYPE = 'MOTHER')
would generate an unknown result for these rows, and they will not be included in the query results. But the entire reason for using the left outer join was to make certain they were included! To solve this problem, the WHERE clause is expanded to also test for, and allow, rows where the parent type is NULL.
7:
Multitable Queries (Joins)
As one final example, suppose you want to generate a girl/boy listing again, but this time you want to include the name of the boy s father and the girl s mother in the query results. This query requires a four-table join (BOYS, GIRLS, and two copies of the PARENTS table, one for joining to the boys information to get father names and one for joining to the girls information to obtain mother names). Again the potential for unmatched rows in the joins means there are several possible right answers to the query. Suppose, as before, that you want to include all girls and boys in the boy/girl pairing, even if the boy or girl does not have a matching row in the PARENTS table. You need to use outer joins for the (BOYS join PARENTS) and (GIRLS join PARENTS) parts of the query, but an inner join for the (BOYS join GIRLS) part of the query. This query yields the desired results:
SELECT FROM ON JOIN ON GIRLS.NAME, MOTHERS.PNAME, BOYS.NAME, FATHERS.PNAME GIRLS LEFT JOIN PARENTS AS MOTHERS ((MOTHERS.CHILD = GIRLS.NAME) AND (MOTHERS.TYPE = 'MOTHER')) BOYS ON (GIRLS.CITY = BOYS.CITY) LEFT JOIN PARENTS AS FATHERS ((FATHERS.CHILD = BOYS.NAME) AND (FATHERS.TYPE = 'FATHER'));
Copyright © OnBarcode.com . All rights reserved.