sql - Alter Column datatype with primary key

Question

I have a ReferenceID varchar(6) column in over 80 different tables. I need to extend this to a varchar(8) throughout the db following a change implemented by the government organisation that assigns the IDs.

I was hoping to declare a cursor to get the table names as follows:

DECLARE @TableName AS VARCHAR(200)
DECLARE TableCursor CURSOR LOCAL READ_ONLY FOR
SELECT t.name AS TableName
    FROM sys.columns c
        JOIN sys.tables t ON c.object_id = t.object_id
    WHERE c.name = 'ReferenceID'

OPEN TableCursor
    FETCH NEXT FROM TableCursor 
    INTO @TableName

and then edit the type as follows:

ALTER TABLE @TableName ALTER COLUMN ReferenceID VARCHAR(8)

This fails because the column is part of the Primary Key in some of the tables (and the columns included in the PK vary from table to table).

I really don't want to have to drop and recreate each PK manually for each table.

Within the cursor, is there a way either to disable the PK before altering the datatype and then re-enable it, or to drop and recreate the PK either side of altering the datatype, bearing in mind that the PK will depend on which table we're currently looking at?

Answer 1

You need to specify NOT NULL explicitly in an ALTER TABLE ... ALTER COLUMN otherwise it defaults to allowing NULL. This is not permitted in a PK column.

The following works fine.

CREATE TABLE p
(
ReferenceID VARCHAR(6) NOT NULL PRIMARY KEY
)

INSERT INTO p VALUES ('AAAAAA')

ALTER TABLE p ALTER COLUMN ReferenceID VARCHAR(8) NOT NULL

when the NOT NULL is omitted it gives the following error

Msg 5074, Level 16, State 1, Line 1
The object 'PK__p__E1A99A792180FB33' is dependent on column 'ReferenceID'.
Msg 4922, Level 16, State 9, Line 1
ALTER TABLE ALTER COLUMN ReferenceID failed because one or more objects access this column.

A couple of things to consider in your programmatic approach is that you would need to drop any foreign keys referencing the ReferenceID columns temporarily and also make sure you don't include the NOT NULL for (Non PK) ReferenceID columns that currently are nullable.