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<h1 align="center">SQL As Understood By SQLite</h1><p><a href="lang.html">[Top]</a></p><h2>ALTER TABLE</h2><h4><a href="syntaxdiagrams.html#alter-table-stmt">alter-table-stmt:</a></h4><blockquote> <img alt="syntax diagram alter-table-stmt" src="images/syntax/alter-table-stmt.gif"></img> </blockquote>
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<p>SQLite supports a limited subset of ALTER TABLE.
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The ALTER TABLE command in SQLite allows the user to rename a table
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or to add a new column to an existing table. It is not possible
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to rename a column, remove a column, or add or remove constraints from a table.
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<p> The RENAME TO syntax is used to rename the table identified by
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<i>[database-name.]table-name</i> to <i>new-table-name</i>.
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cannot be used to move a table between attached databases, only to rename
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a table within the same database.</p>
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<p> If the table being renamed has triggers or indices, then these remain
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attached to the table after it has been renamed. However, if there are
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any view definitions, or statements executed by triggers that refer to
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the table being renamed, these are not automatically modified to use the new
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table name. If this is required, the triggers or view definitions must be
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dropped and recreated to use the new table name by hand.
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<p>If <a href="foreignkeys.html">foreign key constraints</a> are
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<a href="pragma.html#pragma_foreign_keys">enabled</a> when a table is renamed, then any
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<a href="syntaxdiagrams.html#foreign-key-clause">REFERENCES clauses</a> in any table (either the
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table being renamed or some other table)
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that refer to the table being renamed are modified to refer
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to the renamed table by its new name.
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<p> The ADD COLUMN syntax
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is used to add a new column to an existing table.
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The new column is always appended to the end of the list of existing columns.
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The <a href="syntaxdiagrams.html#column-def">column-def</a> rule defines the characteristics of the new column.
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The new column may take any of the forms permissible in a <a href="lang_createtable.html">CREATE TABLE</a>
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statement, with the following restrictions:
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<li>The column may not have a PRIMARY KEY or UNIQUE constraint.</li>
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<li>The column may not have a default value of CURRENT_TIME, CURRENT_DATE,
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CURRENT_TIMESTAMP, or an expression in parentheses.</li>
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<li>If a NOT NULL constraint is specified, then the column must have a
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default value other than NULL.
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<li>If <a href="foreignkeys.html">foreign key constraints</a> are <a href="pragma.html#pragma_foreign_keys">enabled</a> and
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a column with a <a href="syntaxdiagrams.html#foreign-key-clause">REFERENCES clause</a>
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is added, the column must have a default value of NULL.
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<p>Note also that when adding a <a href="lang_createtable.html#ckconst">CHECK constraint</a>, the CHECK constraint
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is not tested against preexisting rows of the table.
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This can result in a table that contains data that
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is in violation of the CHECK constraint. Future versions of SQLite might
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change to validate CHECK constraints as they are added.</p>
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<p> The execution time of the ALTER TABLE command is independent of
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the amount of data in the table. The ALTER TABLE command runs as quickly
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on a table with 10 million rows as it does on a table with 1 row.
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<p>After ADD COLUMN has been run on a database, that database will not
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be readable by SQLite version 3.1.3 and earlier.</p>
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