barcode maker vb.net Subqueries and Query Expressions in Software

Printing ANSI/AIM Code 128 in Software Subqueries and Query Expressions

Subqueries and Query Expressions
Code128 Scanner In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Code 128C Drawer In None
Using Barcode generator for Software Control to generate, create Code128 image in Software applications.
that return a full table of results. One useful role for table-valued subqueries is within the WHERE or HAVING clause, where it is combined with extended forms of the subquery tests. For example, suppose you wanted to list the descriptions and prices of all products with orders exceeding $20,000 in the sample database. Perhaps the most straightforward way to express this request is in this SQL2 statement that uses a table-valued subquery: List the description and price of all products with individual orders over $20,000.
Code 128 Scanner In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
Creating Code 128 Code Set A In Visual C#.NET
Using Barcode maker for .NET Control to generate, create Code 128 Code Set C image in .NET applications.
SELECT DESCRIPTION, PRICE FROM PRODUCTS WHERE (MFR_ID,PRODUCT_ID) IN (SELECT MFR, PRODUCT FROM ORDERS WHERE AMOUNT > 20000.00)
Draw Code 128 Code Set C In VS .NET
Using Barcode printer for ASP.NET Control to generate, create ANSI/AIM Code 128 image in ASP.NET applications.
Printing ANSI/AIM Code 128 In .NET
Using Barcode generation for VS .NET Control to generate, create Code 128B image in .NET applications.
RETRIEVING DATA
Code 128 Code Set B Creation In VB.NET
Using Barcode generation for .NET framework Control to generate, create Code 128 image in Visual Studio .NET applications.
Paint GS1 - 12 In None
Using Barcode printer for Software Control to generate, create UPC Symbol image in Software applications.
The top-level query is a straightforward statement of the English-language request it asks for the description and price of those products whose identification (as in previous examples, a manufacturer-ID/product-ID pair) matches some set of products. This is expressed as a subquery set membership test in the WHERE clause. The subquery generates a two-column table of subquery results, which are the identifications of the products that meet the stated order size criterion. It s certainly possible to express this query in other ways. From the discussion in 7, you probably recognize that it can be stated as a join of the PRODUCTS and ORDERS tables with a compound search condition: List the description and price of all products with individual orders over $20,000.
Encoding Barcode In None
Using Barcode creator for Software Control to generate, create bar code image in Software applications.
UPC - 13 Maker In None
Using Barcode generator for Software Control to generate, create EAN 13 image in Software applications.
SELECT FROM WHERE AND AND DESCRIPTION, PRICE PRODUCTS, ORDERS (MFR_ID = MFR) (PRODUCT_ID = PRODUCT) (AMOUNT > 20000.00)
Paint DataMatrix In None
Using Barcode generation for Software Control to generate, create ECC200 image in Software applications.
Paint EAN / UCC - 14 In None
Using Barcode drawer for Software Control to generate, create UCC.EAN - 128 image in Software applications.
This is an equally valid statement of the query, but it s a lot further removed from the English-language request, and therefore more difficult to understand for most people. As queries become more complex, the ability to use table-valued subqueries becomes even more useful to simplify and clarify SQL requests.
Creating Leitcode In None
Using Barcode drawer for Software Control to generate, create Leitcode image in Software applications.
Reading Universal Product Code Version A In Visual C#
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in VS .NET applications.
The SQL2 Query Specification
Bar Code Reader In VB.NET
Using Barcode decoder for .NET framework Control to read, scan read, scan image in .NET framework applications.
Bar Code Drawer In None
Using Barcode creator for Font Control to generate, create bar code image in Font applications.
The SQL2 standard formalizes the definition of what we have loosely been calling a SELECT statement or a query in the last three chapters into a basic building block called a query specification. For a complete understanding of the SQL2 table expression capabilities in the next section, it s useful to understand this formal definition. The
Bar Code Printer In None
Using Barcode maker for Font Control to generate, create barcode image in Font applications.
Code 128B Creation In None
Using Barcode maker for Online Control to generate, create Code 128 image in Online applications.
SQL: The Complete Reference
Encoding EAN13 In Visual Basic .NET
Using Barcode encoder for VS .NET Control to generate, create EAN 13 image in Visual Studio .NET applications.
Create EAN-13 In .NET
Using Barcode maker for VS .NET Control to generate, create EAN13 image in Visual Studio .NET applications.
form of a SQL2 query specification is shown in Figure 9-16. Its components should be familiar from the earlier chapters: I A select list specifies the columns of query results. Each column is specified by an expression that tells the DBMS how to calculate its value. The column can be assigned an optional alias with the AS clause. I The keywords ALL or UNIQUE control duplicate row elimination in the query results. I The FROM clause specifies the tables that contribute to the query results. I The WHERE clause describes how the DBMS should determine which rows are included in the query results and which should be discarded. I The GROUP BY and HAVING clauses together control the grouping of individual query results rows in a grouped query, and the selection of row groups for inclusion or exclusion in the final results. The query specification is the basic query building block in the SQL2 standard. Conceptually, it describes the process of combining data from the tables in the FROM clause into a row/column table of query results. The value of the query specification is a table of data. In the simplest case, a SQL2 query consists of a simple query specification. In a slightly more complex case, a query specification is used to describe a subquery, which appears within another (higher-level) query specification. Finally, query specifications can be combined using table-valued operations to form general-purpose query expressions, as described in the next section.
Figure 9-16.
SQL2 query specification: formal definition
9:
Subqueries and Query Expressions
Query Expressions (SQL2)
The SQL2 standard defines a query expression as the full, general-purpose way that you can specify a table of query results in the SQL2 language. The basic building blocks you can use to create a query expression are the following: I A query specification, as described in the preceding section (SELECT FROM ). Its value is a table of query results. I A table-value constructor, as previously described (VALUES ). Its value is a table of constructed values. I An explicit table reference (TABLE tblname). Its value is the contents of the named table. Using these building blocks, SQL2 lets you combine their table values using the following operations: I JOIN. SQL2 provides explicit support for full cross-product joins (cross joins), natural joins, inner joins, and all types of outer joins (left, right, and full), as described in 7. A JOIN operation takes two tables as its input and produces a table of combined query results according to the join specification. I UNION. The SQL2 UNION operation provides explicit support for merging the rows of two compatible tables (that is, two tables having the same number of columns and with corresponding columns having the same data types). The UNION operation takes two tables as its input and produces a single merged table of query results. I DIFFERENCE. The SQL2 EXCEPT operation takes two tables as its input and produces as its output a table containing the rows that appear in the first table but that do not appear in another table that is, the rows that are missing from the second table. Conceptually, the EXCEPT operation is like table subtraction. The rows of the second table are taken away from the rows of the first table, and the answer is the remaining rows of the first table. I INTERSECT. The SQL2 INTERSECT operation takes two tables as its input and produces as its output a table containing the rows that appear in both input tables.
Copyright © OnBarcode.com . All rights reserved.