Is it possible to add multiple columns to a table in a single query execution, using alter table in exasol?
example:
Alter table Employee add column phone_number varchar(256), add column address varchar(256)
It is not possible in one command in Exasol, but in Exasol DDL commands do not auto-commit, so you can put them in the same transaction. You could do:
set autocommit off;
alter table t1 add column c1 varchar(100);
alter table t1 add column c2 varchar(100);
alter table t1 add column c3 varchar(100);
commit;
set autocommit on;
No. According to the documentation it is impossible.
Related
I have a Snowflake stored procedure and I want to use "insert into" without hard coding column names.
INSERT INTO MEMBERS_TARGET (ID, NAME)
SELECT ID, NAME
FROM MEMBERS_STREAM;
This is what I have and column names are hardcoded. The query should copy data from MEMBERS_STREAM to MEMBERS_TARGET. The stream has more columns such as
METADATA$ACTION | METADATA$ISUPDATE | METADATA$ROW_ID
which I am not intending to copy.
I don't know of a way to not copy the METADATA columns if not hardcoding. However if you don't want the data maybe the easiest thing to do is to add them to your target, INSERT using a SELECT * and later in the sp set them to NULL.
Alternatively, earlier in your sp, run an ALTER TABLE ADD COLUMN to add the columns, INSERT using SELECT * and then after that run an ALTER TABLE DROP COLUMN to remove the columns? That way your table structure stays the same, albeit briefly it will have some extra columns.
A SELECT * is not usually recommended but it's the easiest alternative I can think of
Suppose I have following schema.
create table tb1
(col1 Integer,
col2 varchar(50)
) in dbspace1 extent size 1000 next 500 lock mode row;
and I want to change the dbspace of above table to dbspace2 . After doing my alteration table schema should be look like as follows .
create table tb1
(col1 Integer,
col2 varchar(50)
) in dbspace2 extent size 1000 next 500 lock mode row;
Is it possible to do? If it is possible what is the command?
On the face of it, the ALTER FRAGMENT statement and the INIT clause allows you to write:
ALTER FRAGMENT ON TABLE tb1 INIT IN dbspace2;
The keyword TABLE is required; you could specify an index instead.
I've not actually experimented to prove that it works, but the syntax diagram certainly allows it.
I have downloaded sqlite manager app in Firefox browser and open sqlite manager app.
1) Created database named DBSQLTEST.
2) Created table named SQLTEST contain has threes fields are SLNO, NAME and AGE
3) Inserted new records
But i want remove a ‘AGE’ column in sqltest table
i using sql command like below
ALTER TABLE SQLTEST DROP COLUMN AGE
SQLiteManager message says
SQLiteManager: Likely SQL syntax error: ALTER TABLE SQLTEST DROP COLUMN AGE [ near "DROP": syntax error ]
Exception Name: NS_ERROR_FAILURE
Exception Message: Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [mozIStorageConnection.createStatement]
What is error that?
sqlite does not support DROP COLUMN in ALTER TABLE. You can only rename tables and add columns.
Reference: http://www.sqlite.org/lang_altertable.html
If you need to remove columns, create a new table, copy the data there, drop the old table and rename the table to its intented name.
SQLite does not fully support ALTER TABLE statements. You can only rename table, or add columns.
If you want to drop a column, your best option is to create a new table without the column, and to drop the old table in order to rename the new one.
For example, suppose you have a table named "t1" with columns names "a", "b", and "c" and that you want to delete column "c" from this table. The following steps illustrate how this could be done:
BEGIN TRANSACTION;
CREATE TEMPORARY TABLE t1_backup(a,b);
INSERT INTO t1_backup SELECT a,b FROM t1;
DROP TABLE t1;
CREATE TABLE t1(a,b);
INSERT INTO t1 SELECT a,b FROM t1_backup;
DROP TABLE t1_backup;
COMMIT;
Credits to Benoit.
Create a table
CREATE TABLE SQLTEST ("SLNO" INTEGER PRIMARY KEY ,"NAME" TEXT,AGE INTEGER)
If want to remove a column
ALTER TABLE SQLTEST RENAME TO SQLTESTCOPY
CREATE TABLE SQLTEST ("SLNO" INTEGER PRIMARY KEY ,"NAME" TEXT)
INSERT INTO SQLTEST"SELECT "SLNO","NAME" FROM SQLTESTCOPY
DROP TABLE SQLTESTCOPY
easy.
I have a database I would like to convert to use UUID's as the primary key in postgresql.
I have roughly 30 tables with deep multi-level associations. Is there an 'easy' way to convert all current ID's to UUID?
From this: https://coderwall.com/p/n_0awq, I can see that I could alter the table in migration. I was thinking something like this:
for client in Client.all
# Retrieve children
underwritings = client.underwritings
# Change primary key
execute 'ALTER TABLE clients ALTER COLUMN id TYPE uuid;'
execute 'ALTER TABLE clients ALTER COLUMN id SET DEFAULT uuid_generate_v1();'
# Get new id - is this already generated?
client_id = client.id
for underwriting in underwritings
locations = underwriting.locations
other_record = underwriting.other_records...
execute 'ALTER TABLE underwritings ALTER COLUMN id TYPE uuid;'
execute 'ALTER TABLE underwritings ALTER COLUMN id SET DEFAULT uuid_generate_v1();'
underwriting.client_id = client_id
underwriting.saved
underwriting_id = underwriting.id
for location in locations
buildings = location.buildings
execute 'ALTER TABLE locations ALTER COLUMN id TYPE uuid;'
execute 'ALTER TABLE locations ALTER COLUMN id SET DEFAULT uuid_generate_v1();'
location.undewriting_id = underwriting_id
location.save
location_id = location.id
for building in buildings
...
end
end
for other_record in other_records
...
end
...
...
end
end
Questions:
Will this work?
Is there an easier way to do this?
Will child records be retrieved properly as long as they are retrieved before the primary key is changed?
Will the new primary key be already generated as soon as the alter table is called?
Thanks very much for any help or tips in doing this.
I found these to be quite tedious. It is possible to use direct queries to PostgreSQL to convert table with existing data.
For primary key:
ALTER TABLE students
ALTER COLUMN id DROP DEFAULT,
ALTER COLUMN id SET DATA TYPE UUID USING (uuid(lpad(replace(text(id),'-',''), 32, '0'))),
ALTER COLUMN id SET DEFAULT uuid_generate_v4()
For other references:
ALTER TABLE students
ALTER COLUMN city_id SET DATA TYPE UUID USING (uuid(lpad(replace(text(city_id),'-',''), 32, '0')))
The above left pads the integer value with zeros and converts to a UUID. This approach does not require id mapping and if needed old id could be retrieved.
As there is no data copying, this approach works quite fast.
To handle these and more complicated case of polymorphic associations please use https://github.com/kreatio-sw/webdack-uuid_migration. This gem adds additional helpers to ActiveRecord::Migration to ease these migrations.
I think trying to do something like this through Rails would just complicate matters. I'd ignore the Rails side of things completely and just do it in SQL.
Your first step is grab a complete backup of your database. Then restore that backup into another database to:
Make sure that your backup works.
Give you a realistic playpen where you can make mistakes without consequence.
First you'd want to clean up your data by adding real foreign keys to match all your Rails associations. There's a good chance that some of your FKs will fail, if they do you'll have to clean up your broken references.
Now that you have clean data, rename all your tables to make room for the new UUID versions. For a table t, we'll refer to the renamed table as t_tmp. For each t_tmp, create another table to hold the mapping from the old integer ids to the new UUID ids, something like this:
create table t_id_map (
old_id integer not null,
new_id uuid not null default uuid_generate_v1()
)
and then populate it:
insert into t_id_map (old_id)
select id from t_tmp
And you'll probably want to index t_id_map.old_id while you're here.
This gives us the old tables with integer ids and a lookup table for each t_tmp that maps the old id to the new one.
Now create the new tables with UUIDs replacing all the old integer and serial columns that held ids; I'd add real foreign keys at this point as well; you should be paranoid about your data: broken code is temporary, broken data is usually forever.
Populating the new tables is pretty easy at this point: simply use insert into ... select ... from constructs and JOIN to the appropriate t_id_map tables to map the old ids to the new ones. Once the data has been mapped and copied, you'll want to do some sanity checking to make sure everything still makes sense. Then you can drop your t_tmp and t_id_map tables and get on with your life.
Practice that process on a copy of your database, script it up, and away you go.
You would of course want to shut down any applications that access your database while you're doing this work.
Didn't want to add foreign keys, and wanted to to use a rails migration. Anyways, here is what I did if others are looking to do this (example for 2 tables, I did 32 total):
def change
execute 'CREATE EXTENSION "uuid-ossp";'
execute <<-SQL
ALTER TABLE buildings ADD COLUMN guid uuid DEFAULT uuid_generate_v1() NOT NULL;
ALTER TABLE buildings ALTER COLUMN guid SET DEFAULT uuid_generate_v1();
ALTER TABLE buildings ADD COLUMN location_guid uuid;
ALTER TABLE clients ADD COLUMN guid uuid DEFAULT uuid_generate_v1() NOT NULL;
ALTER TABLE clients ALTER COLUMN guid SET DEFAULT uuid_generate_v1();
ALTER TABLE clients ADD COLUMN agency_guid uuid;
ALTER TABLE clients ADD COLUMN account_executive_guid uuid;
ALTER TABLE clients ADD COLUMN account_representative_guid uuid;
SQL
for record in Building.all
location = record.location
record.location_guid = location.guid
record.save
end
for record in Client.all
agency = record.agency
record.agency_guid = agency.guid
account_executive = record.account_executive
record.account_executive_guid = account_executive.guid unless account_executive.blank?
account_representative = record.account_representative
record.account_representative_guid = account_representative.guid unless account_representative.blank?
record.save
end
execute <<-SQL
ALTER TABLE buildings DROP CONSTRAINT buildings_pkey;
ALTER TABLE buildings DROP COLUMN id;
ALTER TABLE buildings RENAME COLUMN guid TO id;
ALTER TABLE buildings ADD PRIMARY KEY (id);
ALTER TABLE buildings DROP COLUMN location_id;
ALTER TABLE buildings RENAME COLUMN location_guid TO location_id;
ALTER TABLE clients DROP CONSTRAINT clients_pkey;
ALTER TABLE clients DROP COLUMN id;
ALTER TABLE clients RENAME COLUMN guid TO id;
ALTER TABLE clients ADD PRIMARY KEY (id);
ALTER TABLE clients DROP COLUMN agency_id;
ALTER TABLE clients RENAME COLUMN agency_guid TO agency_id;
ALTER TABLE clients DROP COLUMN account_executive_id;
ALTER TABLE clients RENAME COLUMN account_executive_guid TO account_executive_id;
ALTER TABLE clients DROP COLUMN account_representative_id;
ALTER TABLE clients RENAME COLUMN account_representative_guid TO account_representative_id;
SQL
end
I have to back up a table, which can change number of column. When my etl script starts it doesn't know the number of column. How can I create INSERT INTO table VALUES (?1, ?2, ...) script on the fly?
Regards,
Jacek
Depending on the database, one can use CREATE TABLE FROM SELECT (or similar) to back up the table. Example:
CREATE TABLE new_table AS (SELECT * FROM old_table);