83 lines
4.9 KiB
HTML
83 lines
4.9 KiB
HTML
<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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<meta name="dc.date" scheme="iso8601" content="2005-09-19" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="keywords" content="description, alias" />
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<title>Aliases</title>
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<script language = "Javascript" src = "../rzahg/synch.js" type="text/javascript"></script>
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<a name="ch2alias"></a>
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<h2 id="ch2alias"><a href="rbafzmst02.htm#ToC_94">Aliases</a></h2><a id="idx300" name="idx300"></a>
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<p>An <span class="italic">alias</span> can be thought of as an alternative name
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for a table, partition of a table, view, or member of a database file. A table
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or view in an SQL statement can be referenced by its name or by an alias.
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An alias can only refer to a table, partition of a table, view, or database
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file member within the same relational database.</p>
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<p>An alias can be used wherever a table or view name can be used, except:</p>
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<ul>
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<li>Do not use an alias name where a new table or view name is expected, such
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as in the CREATE TABLE or CREATE VIEW statements. For example, if an alias
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name of PERSONNEL is created, then a subsequent statement such as CREATE TABLE
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PERSONNEL will cause an error.</li>
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<li>An alias that refers to an individual partition of a table or member of
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a database file can only be used in a select statement, CREATE INDEX, DELETE,
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INSERT, SELECT INTO, SET variable, UPDATE, or VALUES INTO statement.</li></ul>
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<p>Aliases can also help avoid using file overrides. Not only does an alias
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perform better than an override, but an alias is also a permanent object that
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only need be created once.</p>
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<p>An alias can be created even though the object that the alias refers to
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does not exist. However, the object must exist when a statement that references
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the alias is executed. A warning is returned if the object does not exist
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when the alias is created. An alias cannot refer to another alias. An alias
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can only refer to a table, partition of a table, view, or database file member
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within the same relational database.</p>
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<p>The option of referring to a table, partition of a table, view, or database
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file member by an alias name is not explicitly shown in the syntax diagrams
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or mentioned in the description of the SQL statements.</p>
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<p>A new alias cannot have the same fully-qualified name as an existing table,
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view, index, file, or alias.</p>
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<p>The effect of using an alias in an SQL statement is similar to that of
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text substitution. The alias, which must be defined before the SQL statement
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is executed, is replaced by the qualified base table, partition of a table,
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view, or database file member name. For example, if PBIRD.SALES is an alias
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for DSPN014.DIST4_SALES_148, then at statement run time:</p>
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<pre class="xmp"> <span class="bold">SELECT * FROM</span> PBIRD.SALES
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</pre>
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<p>effectively becomes</p>
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<pre class="xmp"> <span class="bold">SELECT * FROM</span> DSPN014.DIST4_SALES_148
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</pre>
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<p>The effect of dropping an alias and recreating it to refer to another table
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depends on the statement that references the alias. </p>
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<ul>
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<li>SQL Data or SQL Data Change statements that refer to that alias will be
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implicitly rebound when they are next run.</li>
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<li>If a CREATE VIEW or CREATE INDEX statement refers to an alias, dropping
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and re-creating the alias has no effect on the view or index.</li></ul>
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<p>For syntax toleration of existing DB2 UDB for z/OS applications, SYNONYM can be
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used in place of ALIAS in the CREATE ALIAS and DROP ALIAS statements.</p>
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<hr /><br />
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[ <a href="#Top_Of_Page">Top of Page</a> | <a href="rbafzmstch2nam.htm">Previous Page</a> | <a href="rbafzmstch2auth.htm">Next Page</a> | <a href="rbafzmst02.htm#wq1">Contents</a> |
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