Documentation Source Text

is used to add a new column to an existing table.
^The new column is always appended to the end of the list of existing columns.
The [column-def] rule defines the characteristics of the new column.
^(The new column may take any of the forms permissable in a [CREATE TABLE]
statement, with the following restrictions:)^
<ul>
<li>^The column may not have a PRIMARY KEY or UNIQUE constraint.</li>
<li>^The column may not have a default value of CURRENT_TIME, CURRENT_DATE 
    or CURRENT_TIMESTAMP.</li>
<li>^If a NOT NULL constraint is specified, then the column must have a
    default value other than NULL.
<li>^If [foreign key constraints] are [foreign_keys pragma | enabled] and
    a column with a [foreign-key-clause | REFERENCES clause]
    is added, the column must have a default value of NULL.
</ul>

<p>^Note also that when adding a CHECK constraint, the CHECK constraint
is not tested against preexisting rows of the table.
^This can result in a table that contains data that
is in violation of the CHECK constraint.  Future versions of SQLite might
change to validate CHECK constraints as they are added.</p>

<p> ^The execution time of the ALTER TABLE command is independent of
the amount of data in the table.  The ALTER TABLE command runs as quickly
on a table with 10 million rows as it does on a table with 1 row.
</p>

<p>After ADD COLUMN has been run on a database, that database will not
be readable by SQLite version 3.1.3 and earlier.</p>

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