qr code scanner java app Figure A.1 Example tables with example data in Java

Print QR Code in Java Figure A.1 Example tables with example data

Figure A.1 Example tables with example data
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APPENDIX A
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An SQL update modifies an existing row:
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update ITEM set PRICE = 47.0 where ITEM_ID = 4
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A deletion removes a row:
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delete from ITEM where ITEM_ID = 4
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The real power of SQL lies in querying data. A single query may perform many relational operations on several tables. Let s look at the basic operations. Restriction is the operation of choosing rows of a table that match a particular criterion. In SQL, this criterion is the expression that occurs in the where clause:
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select * from ITEM where NAME like 'F%'
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Projection is the operation of choosing columns of a table and eliminating duplicate rows from the result. In SQL, the columns to be included are listed in the select clause. You can eliminate duplicate rows by specifying the distinct keyword:
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select distinct NAME from ITEM
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A Cartesian product (also called cross join) produces a new table consisting of all possible combinations of rows of two existing tables. In SQL, you express a Cartesian product by listing tables in the from clause:
select * from ITEM i, BID b
A relational join produces a new table by combining the rows of two tables. For each pair of rows for which a join condition is true, the new table contains a row with all field values from both joined rows. In ANSI SQL, the join clause specifies a table join; the join condition follows the on keyword. For example, to retrieve all items that have bids, you join the ITEM and the BID table on their common ITEM_ ID attribute:
select * from ITEM i inner join BID b on i.ITEM_ID = b.ITEM_ID
A join is equivalent to a Cartesian product followed by a restriction. So, joins are often instead expressed in theta style, with a product in the from clause and the join condition in the where clause. This SQL theta-style join is equivalent to the previous ANSI-style join:
select * from ITEM i, BID b where i.ITEM_ID = b.ITEM_ID
Along with these basic operations, relational databases define operations for aggregating rows (GROUP BY) and ordering rows (ORDER BY):
APPENDIX A
select b.ITEM_ID, max(b.AMOUNT) from BID b group by b.ITEM_ID having max(b.AMOUNT) > 15 order by b.ITEM_ID asc
SQL was called a structured query language in reference to a feature called subse-
lects. Because each relational operation produces a new table from an existing table or tables, an SQL query may operate on the result table of a previous query. SQL lets you express this using a single query, by nesting the first query inside the second:
select * from ( select b.ITEM_ID as ITEM, max(b.AMOUNT) as AMOUNT from BID b group by b.ITEM_ID ) where AMOUNT > 15 order by ITEM asc
The result of this query is equivalent to the previous one. A subselect may appear anywhere in an SQL statement; the case of a subselect in the where clause is the most interesting:
select * from BID b where b.AMOUNT >= (select max(c.AMOUNT) from BID c)
This query returns the largest bids in the database. Where clause subselects are often combined with quantification. The following query is equivalent:
select * from BID b where b.AMOUNT >= all(select c.AMOUNT from BID c)
An SQL restriction criterion is expressed in a sophisticated expression language that supports mathematical expressions, function calls, string matching, and perhaps even more sophisticated features such as full-text search:
select * from ITEM i where lower(i.DESCRIPTION) like '%gc%' or lower(i.DESCRIPTION) like '%excellent%'
appendix B: Mapping quick reference
APPENDIX B
Many Hibernate books list all possible XML mapping elements and mapping annotations in an appendix. The usefulness of doing so is questionable. First, this information is already available in a convenient form; you only need to know how to get it. Second, any reference we might add here would be outdated in a matter of months, maybe even weeks. The core Hibernate mapping strategies don t change that often, but little details, options, and attributes are always modified in the process of improving Hibernate. And isn t the main reason you want a mapping reference so you have an upto-date list of all options
You can get a list of all XML mapping elements and attributes bundled with Hibernate in hibernate-mapping-3.0.dtd. Open this file in any text editor, and you ll see that it s fully documented and very readable. You can print it out as a quick reference if you work with XML mapping files. If the syntax of the DTD bothers you, do a few quick search/replace operations on a copy of this file to replace the DTD tags with something you prefer in your printed output. You can get a list of all mapping annotations by reading the Javadoc for the javax.persistence and org.hibernate.annotations packages. The Javadoc is bundled with the Hibernate Annotations package. For example, to get a clickable, up-to-date reference for all Hibernate extension annotations, open api/org/hibernate/annotations/package-summary.html.
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