Here after ALTER TABLE, specify name of table to which you want to modify column, then. Keep in mind however that the default value must satisfy the given constraints, or the ADD will fail. Use ALTER TABLE ALTER COLUMN statement to change data type of column. In fact all the options that can be applied to a column description in CREATE TABLE can be used here. You can: Add columns Remove columns Add constraints Remove constraints Change default values Change column data types Rename columns Rename tables All these actions are performed using the ALTER TABLE command, whose reference page contains details beyond those given here. You can also define constraints on the column at the same time, using the usual syntax:ĪLTER TABLE products ADD COLUMN description text CHECK (description '')
#Postgres alter column data type update#
To avoid a potentially lengthy update operation, particularly if you intend to fill the column with mostly nondefault values anyway, it may be preferable to add the column with no default, insert the correct values using UPDATE, and then add any desired default as described below. However, if the default value is volatile (e.g., clock_timestamp()) each row will need to be updated with the value calculated at the time ALTER TABLE is executed.
Instead, the default value will be returned the next time the row is accessed, and applied when the table is rewritten, making the ALTER TABLE very fast even on large tables.
From PostgreSQL 11, adding a column with a constant default value no longer means that each row of the table needs to be updated when the ALTER TABLE statement is executed.
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