|The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 454 pages
RRP £14.95 ($19.95)
Sales of this book support the PostgreSQL project! Get a printed copy>>>
3.5.6 Changing a Column's Data Type
To convert a column to a different data type, use a command like:
ALTER TABLE products ALTER COLUMN price TYPE numeric(10,2);
This will succeed only if each existing entry in the column can be
converted to the new type by an implicit cast. If a more complex
conversion is needed, you can add a
USING clause that
specifies how to compute the new values from the old.
PostgreSQL will attempt to convert the column's default value (if any) to the new type, as well as any constraints that involve the column. But these conversions might fail, or might produce surprising results. It's often best to drop any constraints on the column before altering its type, and then add back suitably modified constraints afterwards.
|ISBN 9781906966041||The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference||See the print edition|