This section is from the "Practical PostgreSQL" book, by John Worsley and Joshua Drake. Also available from Amazon: Practical PostgreSQL.
Most mature RDBMSs offer methods by which you may alter the properties of existing tables via the ALTER keyword. The PostgreSQL implementation of ALTER TABLE allows for six total types of table modifications as of version 7.1.x:
Adding columns
Setting and removing default column values
Re-naming the table
Re-naming columns
Adding constraints
Changing ownership
 
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