AWS Redshift - Add IDENTITY column to existing table

问题

In AWS Redshift, when attempting to add an IDENTITY column to an existing table using the command

ALTER TABLE table_name ADD COLUMN id bigint IDENTITY(1,1);

I get the following error

ERROR: ALTER TABLE ADD COLUMN does not support columns with type IDENTITY

Which obviously implies that this simply isn't allowed in Redshift. Will I need to drop and recreate the table? Or is there some workaround solution to get this done in Redshift?

回答1:

While you can't do it directly, you can accomplish this in a few steps. If we have existing table t1 defined as:

CREATE TABLE t1 (
c1 vachar(MAX),
c2 int
);

First, create a new table that has the same columns as t1, but with the addition of the identity column that you want to add:

CREATE TABLE t2 (
id bigint IDENTITY(1,1),
c1 varchar(MAX),
c2 int
);

Then, insert all of the rows of t1 into t2, filling every column other than the identity column:

INSERT INTO t2 (c1, c2)
(SELECT * FROM t1);

Now we can drop the original table:

DROP TABLE t1

And finally rename the new table to original table:

ALTER TABLE t2
RENAME TO t1;

回答2:

You must add IDENTITY column during table declaration. And you can't add it later.

Docs: You cannot use an ALTER TABLE ADD COLUMN command to modify the following table and column attributes:
    UNIQUE

    PRIMARY KEY

    REFERENCES (foreign key)

    IDENTITY

回答3:

If all you want to do is add a unique column to an existing table, the following might be useful:

CREATE TABLE tableWithId AS 
(SELECT ROW_NUMBER() OVER () AS id, * FROM originalTable)

It is important to note that this workaround is only valid for adding identity column to existing data. It won't autoincrement when new rows are added.

来源：https://stackoverflow.com/questions/30377165/aws-redshift-add-identity-column-to-existing-table

标签

sql

amazon-redshift