free barcode generator using vb.net Nancy NULL NULL in Software

Draw QR-Code in Software Nancy NULL NULL

Nancy NULL NULL
Read QR Code In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Painting QR Code 2d Barcode In None
Using Barcode encoder for Software Control to generate, create QR image in Software applications.
NULL NULL NULL
Decoding QR In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
Encode QR Code ISO/IEC18004 In Visual C#.NET
Using Barcode printer for .NET Control to generate, create Quick Response Code image in Visual Studio .NET applications.
NULL James George
QR Code Generation In Visual Studio .NET
Using Barcode generation for ASP.NET Control to generate, create QR-Code image in ASP.NET applications.
Denso QR Bar Code Generator In VS .NET
Using Barcode encoder for .NET framework Control to generate, create QR Code image in Visual Studio .NET applications.
NULL Dallas NULL
Making QR Code JIS X 0510 In VB.NET
Using Barcode drawer for Visual Studio .NET Control to generate, create Denso QR Bar Code image in VS .NET applications.
USS-128 Drawer In None
Using Barcode drawer for Software Control to generate, create EAN 128 image in Software applications.
The outer join of the two tables contains eight rows. Four of the rows are identical to those of the inner join between the two tables. Two other rows, for Anne and Nancy, come from the unmatched rows of the GIRLS table. These rows have been NULLextended by matching them to an imaginary row of all NULLs in the BOYS table, and added to the query results. The final two rows, for James and George, come from the unmatched rows of the BOYS table. These rows have also been NULL-extended by matching them to an imaginary row of all NULLs in the GIRLS table and added to the query results. As this example shows, the outer join is an "information-preserving" join. Every row of the BOYS table is represented in the query results (some more than once). Similarly, every row of the GIRLS table is represented in the query results (again, some more than once).
Generate UPC-A In None
Using Barcode creation for Software Control to generate, create UPC Symbol image in Software applications.
Printing Code128 In None
Using Barcode generation for Software Control to generate, create Code128 image in Software applications.
Left and Right Outer Joins *
Bar Code Generator In None
Using Barcode creation for Software Control to generate, create barcode image in Software applications.
Code 39 Full ASCII Creator In None
Using Barcode maker for Software Control to generate, create Code39 image in Software applications.
Technically, the outer join produced by the previous query is called the full outer join of the two tables. Both tables are treated symmetrically in the full outer join. Two other welldefined outer joins do not treat the two tables symmetrically. The left outer join between two tables is produced by following Step 1 and Step 2 in the previous numbered list but omitting Step 3. The left outer join thus includes NULLextended copies of the unmatched rows from the first (left) table but does not include any unmatched rows from the second (right) table. Here is a left outer join between the GIRLS and BOYS tables: List girls and boys in the same city and any unmatched girls. SELECT * FROM GIRLS, BOYS WHERE GIRLS.CITY *= BOYS.CITY GIRLS.NAME ---------Mary Mary Susan Betty Anne Nancy GIRLS.CITY ---------Boston Boston Chicago Chicago Denver NULL BOYS.NAME --------John Henry Sam Sam NULL NULL BOYS.CITY --------Boston Boston Chicago Chicago NULL NULL
EAN8 Creator In None
Using Barcode creator for Software Control to generate, create European Article Number 8 image in Software applications.
Matrix 2D Barcode Encoder In VB.NET
Using Barcode generation for Visual Studio .NET Control to generate, create Matrix 2D Barcode image in VS .NET applications.
The query produces six rows of query results, showing the matched girl/boy pairs and the unmatched girls. The unmatched boys are missing from the results. Similarly, the right outer join between two tables is produced by following Step 1 and Step 3 in the previous numbered list but omitting Step 2. The right outer join thus includes NULL-extended copies of the unmatched rows from the second (right) table but does not include the unmatched rows of the first (left) table. Here is a right outer join between the GIRLS and BOYS tables: List girls and boys in the same city and any unmatched boys. SELECT *
Data Matrix Creation In .NET
Using Barcode printer for ASP.NET Control to generate, create Data Matrix image in ASP.NET applications.
Draw Barcode In None
Using Barcode drawer for Office Word Control to generate, create barcode image in Office Word applications.
- 123 -
ECC200 Creator In None
Using Barcode printer for Font Control to generate, create Data Matrix ECC200 image in Font applications.
Recognize Bar Code In VB.NET
Using Barcode Control SDK for VS .NET Control to generate, create, read, scan barcode image in Visual Studio .NET applications.
FROM GIRLS, BOYS WHERE GIRLS.CITY =* BOYS.CITY GIRLS.NAME ---------Mary Mary Susan Betty NULL NULL GIRLS.CITY ---------Boston Boston Chicago Chicago NULL NULL BOYS.NAME --------John Henry Sam Sam James George BOYS.CITY --------Boston Boston Chicago Chicago Dallas NULL
Create Data Matrix ECC200 In Objective-C
Using Barcode maker for iPad Control to generate, create Data Matrix image in iPad applications.
GS1-128 Generation In None
Using Barcode generator for Office Word Control to generate, create UCC - 12 image in Office Word applications.
This query also produces six rows of query results, showing the matched girl/boy pairs and the unmatched boys. This time the unmatched girls are missing from the results. As noted before, the left and right outer joins do not treat the two joined tables symmetrically. It is often useful to think about one of the tables being the "major" table (the one whose rows are all represented in the query results) and the other table being the "minor" table (the one whose columns contain NULL values in the joined query results). In a left outer join, the left (first-mentioned) table is the major table, and the right (later-named) table is the minor table. The roles are reversed in a right outer join (right table is major, left table is minor). In practice, the left and right outer joins are more useful than the full outer join, especially when joining data from two tables using a parent/child (primary key/foreign key) relationship. To illustrate, consider once again the sample database. We have already seen one example involving the SALESREPS and OFFICES table. The REP_OFFICE column in the SALESREPS table is a foreign key to the OFFICES table; it tells the office where each salesperson works, and it is allowed to have a NULL value for a new salesperson who has not yet been assigned to an office. Tom Snyder is such a salesperson in the sample database. Any join that exercises this SALESREPS-toOFFICES relationship and expects to include data for Tom Snyder must be an outer join, with the SALESREPS table as the major table. Here is the example used earlier: List the salespeople and the cities where they work. SELECT NAME, CITY FROM SALESREPS, OFFICES WHERE REP_OFFICE *= OFFICE NAME ------------Tom Snyder Mary Jones Sam Clark Bob Smith Paul Cruz Dan Roberts Bill Adams Sue Smith Larry Fitch Nancy Angelli CITY -------NULL New York New York Chicago Chicago Chicago Atlanta Los Angeles Los Angeles Denver
Note in this case (a left outer join), the "child" table (SALESREPS, the table with the foreign key) is the major table in the outer join, and the "parent" table (OFFICES) is the
- 124 -
minor table. The objective is to retain rows containing NULL foreign key values (like Tom Snyder's) from the child table in the query results, so the child table becomes the major table in the outer join. It doesn't matter whether the query is actually expressed as a left outer join (as it was previously) or as a right outer join like this: List the salespeople and the cities where they work. SELECT NAME, CITY FROM SALESREPS, OFFICES WHERE OFFICE =* REP_OFFICE NAME ------------Tom Snyder Mary Jones Sam Clark Bob Smith Paul Cruz Dan Roberts Bill Adams Sue Smith Larry Fitch Nancy Angelli CITY --------NULL New York New York Chicago Chicago Chicago Atlanta Los Angeles Los Angeles Denver
What matters is that the child table is the major table in the outer join. There are also useful joined queries where the parent is the major table and the child table is the minor table. For example, suppose the company in the sample database opens a new sales office in Dallas, but initially the office has no salespeople assigned to it. If you want to generate a report listing all of the offices and the names of the salespeople who work there, you might want to include a row representing the Dallas office. Here is the outer join query that produces those results: List the offices and the salespeople who work in each one. SELECT CITY, NAME FROM OFFICES, SALESREPS WHERE OFFICE *= REP_OFFICE CITY ----------New York New York Chicago Chicago Chicago Atlanta Los Angeles Los Angeles Denver Dallas NAME ---------Mary Jones Sam Clark Bob Smith Paul Cruz Dan Roberts Bill Adams Sue Smith Larry Fitch Nancy Angelli NULL
In this case, the parent table (OFFICES) is the major table in the outer join, and the child table (SALESREPS) is the minor table. The objective is to insure that all rows from the
- 125 -
OFFICES table are represented in the query results, so it plays the role of major table. The roles of the two tables are precisely reversed from the previous example. Of course, the row for Tom Snyder, which was included in the query results for the earlier example (when SALESREPS was the major table), is missing from this set of query results because SALESREPS is now the minor table.
Outer Join Notation *
Because the outer join was not part of the SQL1 standard and was not implemented in early IBM SQL products, the DBMS vendors who support the outer join have used various notations in their SQL dialects. The "*=*" notation used in the earlier examples of this section is used by SQL Server. This notation indicates an outer join by appending an asterisk (*) to the comparison test in the WHERE clause that defines the join condition. To indicate the full outer join between two tables, TBL1 and TBL2, on columns COL1 and COL2, an asterisk (*) is placed before and after the standard join operator. The resulting full outer join comparison test looks like this: WHERE COL1 *=* COL2 To indicate a left outer join of TBL1 to TBL2, only the leading asterisk is specified, giving a comparison test like this: WHERE COL1 *= COL2 To indicate a right outer join of TBL1 to TBL2, only the trailing asterisk is specified, giving a comparison test like this: WHERE COL1 =* COL2 An outer join can be used with any of the comparison operators using the same notation. For example, a left outer join of TBL1 to TBL2 using a greater than or equal (>=) comparison would produce a comparison test like this: WHERE COL1 *>= COL2 Oracle also supports the outer join operation but uses a different notation. This notation indicates the outer join in the WHERE clause by including a parenthesized plus sign following the column whose table is to have the imaginary NULL row added (that is, the minor table in the outer join). The left outer join of TBL1 to TBL2 produces a search condition that looks like this: WHERE COL1 = COL2 (+) and the right outer join of TBL1 to TBL2 produces a search condition that looks like this: WHERE COL1 (+) = COL2 Note that the plus sign appears on the opposite side of the comparison from where the asterisk appears in the SQL Server notation. Oracle does not support a full outer join, but as indicated earlier, this does not diminish the practical usefulness of the Oracle outer join capability. Although both of these outer join notations are relatively convenient, they're also somewhat deceiving. Recall that the rules for multi-table SQL query processing begin by examining the FROM clause of a query and conceptually building the product of the two (or more) tables. Only after the product table is constructed does the DBMS start eliminating rows that do not meet the WHERE clause search condition. But with the SQL
- 126 -
Server or Oracle notation, the FROM clause doesn't tell the DBMS whether to build a product table that is only the inner join or one that includes the NULL-extended rows of an outer join. To determine this, the DBMS must "look ahead" to the WHERE clause. A more serious problem is that a join between two tables may involve more than one pair of matching columns, and it's not clear how the notation should be used when there are two or three matching column pairs. Other problems with the outer join notation arise when it is extended to three or more tables. It's easy to extend the notion of an outer join to three tables: TBL1 OUTER-JOIN TBL2 OUTER-JOIN TBL3 This is a perfectly legitimate set of database operations according to the theory of relational databases. But the result depends upon the order in which the outer join operations are performed. The results of: (TBL1 OUTER-JOIN TBL2) OUTER-JOIN TBL3 will in general be different from the results of: TBL1 OUTER-JOIN (TBL2 OUTER-JOIN TBL3) Using either the SQL Server or Oracle notations, it's impossible to specify the evaluation order of the outer joins. Because of this, the results produced by the outer join of three or more tables depend upon the specifics of the DBMS implementation.
Copyright © OnBarcode.com . All rights reserved.