alter-table

I have a column with the type of Varchar in my Postgres database which I meant to be integers... and now I want to change them, unfortunately this doesn't seem to work using my rails migration. change_column :table1, :columnB, :integer Which seems to output this SQL: ALTER TABLE table1 ALTER COLUMN columnB TYPE integer So I tried doing this: execute 'ALTER TABLE table1 ALTER COLUMN columnB TYPE integer USING CAST(columnB AS INTEGER)' but cast doesn't work in this instance because some of the column are null... any ideas? Error: PGError: ERROR: invalid input syntax for integer: "" : ALTER TABLE

How to alter an existing table in MySQL, setting foreign key to another table, using the command line? You have to drop existing foreign key and create another one. For example like this: ALTER TABLE my_table DROP FOREIGN KEY my_key; ALTER TABLE my_table ADD CONSTRAINT my_key FOREIGN KEY ('some_id') REFERENCES some_new_table ('some_other_id') ON UPDATE CASCADE ON DELETE CASCADE; Execute help alter table at mysql command prompt and the output is very much self explanatory. Look for add constraint with foreign key clause and apply it on your table. mysql> help alter table Name: 'ALTER TABLE'

I am trying to create a new column in an existing table, and using a select statement to do division to create the data I want to insert into my new column. Several of the statements I have written out will work as separate queries but I have not been able to string together the statements into one single query. I am still learning SQL and using it with mySQL and PostgreSQL. I took a class last month on SQL and now I am trying to do my own projects to keep my skills sharp. I am doing some work with elections results from 2012 in MN to use in my tables, to understand data I am working with. I

This is the schema of my table: create table LPCG(ID integer primary key, PCG text, Desc text, test text); I wish to drop the column "test", and hence use the command: alter table LPCG drop column test; This is the error message I get: Error: near "drop": syntax error Can someone please help me correct my error? An additional question is: I understand that ID is the primary key attribute. Would I be able to drop that column? If not, is there a workaround which anyone has used? Thanks in advance for any help. SQLite does not fully support ALTER TABLE statements . You can only rename table, or

I think I read somewhere that running an ALTER TABLE foo ADD COLUMN baz text on a postgres database will not cause a read or write lock. Setting a default value causes locking, but allowing a null default prevents a lock. I can't find this in the documentation, though. Can anyone point to a place that says, definitively, if this is true or not? The different sorts of locks and when they're used are mentioned in the doc in Table-level Locks . For instance, Postgres 11's ALTER TABLE may acquire a SHARE UPDATE EXCLUSIVE , SHARE ROW EXCLUSIVE , or ACCESS EXCLUSIVE lock. Postgres 9.1 through 9.3