How to add new column and update its value from another table's column with conditions ?
I'm having two tables named user
id: integer
name: string
preferred_communication_channel_id: integer // stores the id of communication_channel
and table communication_channel stores different communication channels like Email,Telephone,etc.. of user
id: integer
user_id: integer
type: string
Now I need to add new column communication_mode in the user table
And update the column communication_mode value from communication_channel.type with some constraints
Here goes the mysql version of the update
update user as p
join communication_channel as cc
on p.preferred_communication_channel_id = cc.id and p.id=cc.user_id and cc.type="Telephone"
set p.communication_mode=3
I've created a migration to add new column but how to implement this query in rails migration ?
Please correct me if I missed anything
In migrations you can just write execute "SELECT * FROM bananas" and the SQL will be executed!
Related
I am working on a Ruby on Rails app. We are using a PostgreSQL database.
There is a table named scores with the following columns:
Column | Type
--------------+-----------------------
id | integer
value | double precision
ran_at | timestamp
active | boolean
build_id | bigint
metric_id | integer
platform_id | integer
mode_id | integer
machine_id | integer
higher_better | boolean
job_id | integer
variation_id | integer
step | character varying(255)
I need to add a sequence to job_id (note: there is no model for job).
How do I create this sequence?
Use CREATE SEQUENCE:
CREATE SEQUENCE scores_job_id_seq; -- = default name for plain a serial
Then add a column default to scores.job_id:
ALTER TABLE scores ALTER COLUMN job_id SET DEFAULT nextval('scores_job_id_seq');
If you want to bind the sequence to the column (so it is deleted when the column is deleted), also run:
ALTER SEQUENCE scores_job_id_seq OWNED BY scores.job_id;
All of this can be replaced with using the pseudo data type serial for the column job_id to begin with:
Safely and cleanly rename tables that use serial primary key columns in Postgres?
If your table already has rows, you may want to set the SEQUENCE to the next highest value and fill in missing serial values in the table:
SELECT setval('scores_job_id_seq', COALESCE(max(job_id), 1)) FROM scores;
Optionally:
UPDATE scores
SET job_id = nextval('scores_job_id_seq')
WHERE job_id IS NULL;
How to check a sequence efficiently for used and unused values in PostgreSQL
Postgres manually alter sequence
How to reset postgres' primary key sequence when it falls out of sync?
The only remaining difference, a serial column is also set to NOT NULL. You may or may not want that, too:
ALTER TABLE scores ALTER COLUMN job_id SET NOT NULL;
But you cannot just alter the type of an existing integer:
ALTER TABLE scores ALTER job_id TYPE serial;
serial is not an actual data type. It's just a notational convenience feature for CREATE TABLE.
In Postgres 10 or later consider an IDENTITY column:
Auto increment table column
So I figured out how to do this using ActiveRecord migrations on Ruby on Rails. I basically used Erwin's commands and help from this page and put them in the migration files. These are the steps:
1.
In the terminal, type:
rails g migration CreateJobIdSequence
rails g migration AddJobIdSequenceToScores
2.
Edit the migration files as follows:
20140709181616_create_job_id_sequence.rb :
class CreateJobIdSequence < ActiveRecord::Migration
def up
execute <<-SQL
CREATE SEQUENCE job_id_seq;
SQL
end
def down
execute <<-SQL
DROP SEQUENCE job_id_seq;
SQL
end
end
20140709182313_add_job_id_sequence_to_scores.rb :
class AddJobIdSequenceToScores < ActiveRecord::Migration
def up
execute <<-SQL
ALTER SEQUENCE job_id_seq OWNED BY scores.job_id;
ALTER TABLE scores ALTER COLUMN job_id SET DEFAULT nextval('job_id_seq');
SQL
end
def down
execute <<-SQL
ALTER SEQUENCE job_id_seq OWNED BY NONE;
ALTER TABLE scores ALTER COLUMN job_id SET NOT NULL;
SQL
end
end
3.
Migrate the database. In the terminal type:
rake db:migrate
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
Im using sqlite db in a sample rails application. From my users table, i have cleared all records using User.delete_all. But now whenever i insert a new record in the table using User.create, the id is starting at a value which is one more than the id of the last record which was there in the table. For example, if my table had 5 records and i cleared all, then when i do User.create, its starting at id 6.
Is there any way i can make the id start from 1 again ?
Thank You
Similar question : How to reset a single table in rails? . We can run the following at rails console to reset id column to 1 for a sqlite table
ActiveRecord::Base.connection.execute("DELETE from sqlite_sequence where name = '<table_name>'")
You seem to have autoincrement turned on for the id column.
Sqlite handles these values in an internal table called sqlite_sequence. You could reset the id for a particular autoincrement-enabled table by querying:
UPDATE "sqlite_sequence" SET "seq" = 0 WHERE "name" = $YOURTABLENAME
However, this is not a good idea because the autoincrement functionality is intended to be used in a way that the user does not influence its algorithm. Ideally, you should not care about the actual value of your id but consider it only as a unique identifier for a record.
I'm writing a migration to convert a non-rails app into the right format for rails - one of the tables for some reason does not have auto increment set on the id column. Is there a quick way to turn it on while in a migration, maybe with change_column or something?
You need to execute an SQL statement.
statement = "ALTER TABLE `users` CHANGE `id` `id` SMALLINT( 5 ) UNSIGNED NOT NULL AUTO_INCREMENT"
ActiveRecord::Base.connection.execute(statement)
Note this is just an example. The final SQL statement syntax depends on the database.
If you're on postgesql, a single request won't make it. You'll need to create a new sequence in the database.
create sequence users_id_seq;
Then add the id column to your table
alter table users
add id INT UNIQUE;
Then set the default value for the id
alter table users
alter column id
set default nextval('users_id_seq');
Then populate the id column. This may be quite long if the table has many rows
update users
set id = nextval('users_id_seq');
Hope this helps postgresql users...
The Postgres answer by #jlfenaux misses out on the serial type, which does all of it for you automatically:
ALTER TABLE tbl add tbl_id serial;
More details in this related answer.