I am using following query:
ALTER TABLE presales ALTER COLUMN code TYPE numeric(10,0);
to change the datatype of a column from character(20) to numeric(10,0) but I am getting the error:
column "code" cannot be cast to type numeric
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3 Answers
You can try using USING:
The optional
USINGclause specifies how to compute the new column value from the old; if omitted, the default conversion is the same as an assignment cast from old data type to new. AUSINGclause must be provided if there is no implicit or assignment cast from old to new type.
So this might work (depending on your data):
alter table presales alter column code type numeric(10,0) using code::numeric;
-- Or if you prefer standard casting...
alter table presales alter column code type numeric(10,0) using cast(code as numeric);
This will fail if you have anything in code that cannot be cast to numeric; if the USING fails, you'll have to clean up the non-numeric data by hand before changing the column type.
7 Comments
Rishi Bharadwaj
this column is used as a foreign key in another table, i guess i will have to change the datatype of that too?
mu is too short
@user728630: You'll have to drop the FK, change both columns, and then add the FK back. You do have a test database to play with and a backup of the production database, right?
Rishi Bharadwaj
i deleted the foreign key constraint , changed the datatype but after that unable to add the FK. Getting the following error ERROR: insert or update on table "invoices" violates foreign key constraint "invoice_presale_fk" DETAIL: Key (sale,cpf_cnpj)=(4,05943560000101) is not present in table "presales".
mu is too short
@funwhilelost That's a type cast. The linked ALTER TABLE docs cover what you can use with USING.
funwhilelost
@muistooshort I see from the docs it's actually an expression. That makes more sense. The type cast caught me off guard. I ended up with
TYPE varchar(255) USING (substring(formertextcolumn from 1 for 255)) |
If your VARCHAR column contains empty strings (which are not the same as NULL for PostgreSQL as you might recall) you will have to use something in the line of the following to set a default:
ALTER TABLE presales ALTER COLUMN code TYPE NUMERIC(10,0)
USING COALESCE(NULLIF(code, '')::NUMERIC, 0);
(found with the help of this answer)
Comments
Step 1: Add new column with integer or numeric as per your requirement
Step 2: Populate data from varchar column to numeric column
Step 3: drop varchar column
Step 4: change new numeric column name as per old varchar column
