73 lines
5.0 KiB
HTML
73 lines
5.0 KiB
HTML
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<meta name="DC.Title" content="Change a table definition" />
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<meta name="abstract" content="Changing the definition of a table allows you to add new columns, change an existing column definition (change its length, default value, and so on), drop existing columns, and add and remove constraints." />
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<meta name="description" content="Changing the definition of a table allows you to add new columns, change an existing column definition (change its length, default value, and so on), drop existing columns, and add and remove constraints." />
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<title>Change a table definition</title>
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<body id="rbafyalter"><a name="rbafyalter"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Change a table definition</h1>
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<div><p>Changing the definition of a table allows you to add new columns,
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change an existing column definition (change its length, default value, and
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so on), drop existing columns, and add and remove constraints.</p>
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<div class="section"><p>Table definitions are changed using the SQL ALTER TABLE statement.</p>
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</div>
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<div class="section"><p>You can add, change, or drop columns and add or remove constraints
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all with one ALTER TABLE statement. However, a single column can be referenced
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only once in the ADD COLUMN, ALTER COLUMN, and DROP COLUMN clauses. That is,
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you cannot add a column and then alter that column in the same ALTER TABLE
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statement.</p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rbafyaddcol.htm">Add a column</a></strong><br />
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When you add a new column to a table, the column is initialized with its default value for all existing rows. If NOT NULL is specified, a default value must also be specified.</li>
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<li class="ulchildlink"><strong><a href="rbafychgcol.htm">Change a column</a></strong><br />
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You can change a column definition in a table using the ALTER COLUMN clause of the ALTER TABLE statement.</li>
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<li class="ulchildlink"><strong><a href="rbafyallowable.htm">Allowable conversions</a></strong><br />
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When you change the data type of an existing column, the old and new attributes must be compatible.</li>
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<li class="ulchildlink"><strong><a href="rbafydelcol.htm">Delete a column</a></strong><br />
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You can delete a column using the DROP COLUMN clause of the ALTER TABLE statement.</li>
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<li class="ulchildlink"><strong><a href="rbafyorderop.htm">Order of operations for ALTER TABLE statement</a></strong><br />
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An ALTER TABLE statement is performed as this set of steps shows.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafysqltech.htm" title="Data definition language (DDL) describes the portion of SQL that allows you to create, alter, and destroy database objects. These database objects include schemas, tables, views, sequences, catalogs, indexes, and aliases.">Data definition language (DDL)</a></div>
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</div>
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<div class="relinfo"><strong>Related information</strong><br />
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<div><a href="../db2/rbafzmstatabl.htm">ALTER TABLE</a></div>
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</div>
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</div>
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</body>
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