|PostgreSQL Reference Manual - Volume 1 - SQL Language Reference|
by The PostgreSQL Global Development Group
Paperback (6"x9"), 716 pages
RRP £32.00 ($49.95)
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3.5.6 Changing a Column's Data Type
To convert a column to a different data type, use a command like this:
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 may fail, or may 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 0954612027||PostgreSQL Reference Manual - Volume 1 - SQL Language Reference||See the print edition|