free barcode generator in vb.net Qualified Column Names in Software

Generate ANSI/AIM Code 128 in Software Qualified Column Names

Qualified Column Names
Recognizing Code-128 In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Printing Code 128 Code Set C In None
Using Barcode printer for Software Control to generate, create Code 128 Code Set C image in Software applications.
The sample database includes several instances where two tables contain columns with the same name. The OFFICES table and the SALESREPS table, for example, both have a column named SALES. The column in the OFFICES table contains year-to-date sales for each office; the one in the SALESREPS table contains year-to-date sales for each salesperson. Normally, there is no confusion between the two columns, because the FROM clause determines which of them is appropriate in any given query, as in these examples:
Read Code 128 Code Set B In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
Paint Code 128C In Visual C#
Using Barcode maker for .NET Control to generate, create ANSI/AIM Code 128 image in VS .NET applications.
7:
Draw Code 128 In .NET
Using Barcode generator for ASP.NET Control to generate, create Code 128C image in ASP.NET applications.
Code-128 Encoder In VS .NET
Using Barcode drawer for .NET framework Control to generate, create Code 128 Code Set B image in VS .NET applications.
Multitable Queries (Joins)
Generating ANSI/AIM Code 128 In VB.NET
Using Barcode creation for VS .NET Control to generate, create Code 128B image in Visual Studio .NET applications.
Code 39 Full ASCII Maker In None
Using Barcode creation for Software Control to generate, create Code-39 image in Software applications.
Show the cities where sales exceed target.
Make UPCA In None
Using Barcode encoder for Software Control to generate, create Universal Product Code version A image in Software applications.
EAN13 Encoder In None
Using Barcode generator for Software Control to generate, create European Article Number 13 image in Software applications.
SELECT CITY, SALES FROM OFFICES WHERE SALES > TARGET
Painting Bar Code In None
Using Barcode creation for Software Control to generate, create barcode image in Software applications.
UCC.EAN - 128 Creator In None
Using Barcode creation for Software Control to generate, create EAN / UCC - 14 image in Software applications.
Show all salespeople with sales over $350,000.
Drawing Delivery Point Barcode (DPBC) In None
Using Barcode generator for Software Control to generate, create Postnet 3 of 5 image in Software applications.
Barcode Decoder In Java
Using Barcode Control SDK for BIRT reports Control to generate, create, read, scan barcode image in BIRT applications.
SELECT NAME, SALES FROM SALESREPS WHERE SALES > 350000.00
Painting Code 128 In VB.NET
Using Barcode creator for VS .NET Control to generate, create ANSI/AIM Code 128 image in Visual Studio .NET applications.
Barcode Printer In C#.NET
Using Barcode printer for .NET Control to generate, create barcode image in .NET framework applications.
RETRIEVING DATA
Create Code 128 Code Set A In Java
Using Barcode drawer for Android Control to generate, create Code 128A image in Android applications.
Drawing EAN13 In None
Using Barcode creation for Font Control to generate, create EAN / UCC - 13 image in Font applications.
However, here is a query where the duplicate names cause a problem: Show the name, sales, and office for each salesperson.
Drawing Code-39 In Visual Studio .NET
Using Barcode generator for Reporting Service Control to generate, create Code 39 Extended image in Reporting Service applications.
Drawing UPC - 13 In VS .NET
Using Barcode creator for VS .NET Control to generate, create EAN 13 image in .NET framework applications.
SELECT NAME, SALES, CITY FROM SALESREPS, OFFICES WHERE REP_OFFICE = OFFICE Error: Ambiguous column name "SALES"
Although the English description of the query implies that you want the SALES column in the SALESREPS table, the SQL query is ambiguous. The DBMS has no way of knowing whether you want the SALES column from the SALESREPS table or the one from the OFFICES table, since both are contributing data to the query results. To eliminate the ambiguity, you must use a qualified column name to identify the column. Recall from 5 that a qualified column name specifies the name of a column and the table containing the column. The qualified names of the two SALES columns in the sample database are:
OFFICES.SALES and SALESREPS.SALES
A qualified column name can be used in a SELECT statement anywhere that a column name is permitted. The table specified in the qualified column name must, of course, match one of the tables specified in the FROM list. Here is a corrected version of the previous query that uses a qualified column name: Show the name, sales, and office for each salesperson.
SELECT NAME, SALESREPS.SALES, CITY FROM SALESREPS, OFFICES WHERE REP_OFFICE = OFFICE
SQL: The Complete Reference
NAME SALESREPS.SALES CITY -------------- ---------------- -----------Mary Jones $392,725.00 New York Sam Clark $299,912.00 New York Bob Smith $142,594.00 Chicago Paul Cruz $286,775.00 Chicago Dan Roberts $305,673.00 Chicago Bill Adams $367,911.00 Atlanta Sue Smith $474,050.00 Los Angeles Larry Fitch $361,865.00 Los Angeles Nancy Angelli $186,042.00 Denver
Using qualified column names in a multitable query is always a good idea. The disadvantage, of course, is that they make the query text longer. When using interactive SQL, you may want to first try a query with unqualified column names and let SQL find any ambiguous columns. If SQL reports an error, you can edit your query to qualify the ambiguous columns.
All-Column Selections
As discussed in 6, SELECT * can be used to select all columns of the table named in the FROM clause. In a multitable query, the asterisk selects all columns of all tables in the FROM clause. The following query, for example, would produce fifteen columns of query results the nine columns from the SALESREPS table followed by the six columns from the OFFICES table: Tell me all about salespeople and the offices where they work.
SELECT * FROM SALESREPS, OFFICES WHERE REP_OFFICE = OFFICE
Obviously, the SELECT * form of a query becomes much less practical when there are two, three, or more tables in the FROM clause. Many SQL dialects treat the asterisk as a special kind of wildcard column name that is expanded into a list of columns. In these dialects, the asterisk can be qualified with a table name, just like a qualified column reference. In the following query, the select item SALESREPS.* is expanded into a list containing only the columns found in the SALESREPS table: Tell me all about salespeople and the places where they work.
7:
Multitable Queries (Joins)
SELECT SALESREPS.*, CITY, REGION FROM SALESREPS, OFFICES WHERE REP_OFFICE = OFFICE
The query would produce eleven columns of query results the nine columns of the SALESREPS table, followed by the two other columns explicitly requested from the OFFICES table. This type of qualified all-columns select item is supported in many, but not all brands of SQL-based DBMS. It was not allowed by the SQL1 standard but is part of the ANSI/ISO SQL2 specification.
Copyright © OnBarcode.com . All rights reserved.