8/17/2023 0 Comments Psql add column![]() ![]() The ALTER TABLE statement is also used to add and drop various constraints on an existing table. The ALTER TABLE statement is used to add, delete, or modify columns in an existing table. Alternatively, you can add constraints later (see below) after you've filled in the new column correctly. To add a column to an existing table, we have to use the ALTER TABLE statement. This works for both regular and distributed hypertables. Keep in mind however that the default value must satisfy the given constraints, or the ADD will fail. You can alter a hypertable, for example to add a column, by using the PostgreSQL ALTER TABLE command. ![]() In fact all the options that can be applied to a column description in CREATE TABLE can be used 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 '') 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. The syntax of the RETURNING list is identical to that of the output list of SELECT. ![]() The new (post-update) values of the table's columns are used. 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. Any expression using the table's columns, and/or columns of other tables mentioned in FROM, can be computed. 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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