We have a very large table (1 Million records) in some cases and we need to add boolean fields to it which have default values.
If we add only column it takes 3 minutes and we add 3 columns in the same statement it takes same time.
$ALTER TABLE Job ADD COLUMN test BOOLEAN NOT NULL default false;
ALTER TABLE
Time: 186506.603 ms
$ALTER TABLE Job ADD COLUMN test BOOLEAN NOT NULL default false ,
ADD COLUMN test1 BOOLEAN NOT NULL default false,
ADD COLUMN test2 BOOLEAN NOT NULL default false;
ALTER TABLE
Time: 179055.546 ms
We are on Postgres 9.1 . Is there a postgres feature allows to add multiple boolean fields with default values in one shot? This is for a database change management /upgrade solution . Is it better than using temp table to copy and insert to add multiple boolean fields with default values to a table ? The temp table approach is described in this blog:
http://blog.codacy.com/2015/05/14/how-to-update-large-tables-in-postgresql/
You've already shown the best (simple) way - a compound ALTER TABLE statement that adds them all at once.
To do it without a long lock, you have to do it in multiple steps. Add the column as nullable without the default. Add the default but leave it nullable. UPDATE all existing rows to add the new value, preferably in batches. Then finally alter the table to add the not null constraint.
Related
Does CockroachDB support default values for columns in its tables? Does it allow default values to be function values (e.g. current_date())?
You can set DEFAULT values using the DEFAULT constraint, which CockroachDB has documented here.
It also supports setting the default value as a function, e.g. to insert the date that a write occurred.
You would create a table with such a default column like:
CREATE TABLE purchase_log (
id INT PRIMARY KEY,
date_purchased DATE DEFAULT current_date()
);
Then all inserts to the table that don't specify the date_purchased column will have the column automatically populated with the return value of current_date() at the time of the insert.
I created a table named- books and have a column in that by the title 'color' . Initially I have null values in the column 'color'. Now, when I run the following query :
alter table books modify color default 'blue';
schema is formed but on doing select *from books , all the values in column color are still null. What would be the correct query to fire?
here is the link:
http://sqlfiddle.com/#!4/f4210/1
Of course. Alter table just changes the table structure but not the content. New entries will get the default.
To update the existing values run a sql-update query like:
update books set color='blue' where colore is null;
If you now inserting into table then only will come with default values. This statement don't know about previous contents of this table. In non technical language, you are telling oracle to do so now on-wards. This statement will not perform check to old values.
alter is ok for the next values to be inserted: try to insert lines without specifying a value for column color, value should be blue.
But this does not work for existing values, for which you just need an update:
update books set color = 'blue';
Hi this query will be used to add column with default value in existing table in oracle.
alter table <table_name> add <column_name> <contraint> default <default_value> not null;
example:
alter table books add record_status number(1,0) default 1 not null;
alter table books add color varchar(20) default 'blue' not null;
I have a column with REAL data type, and I'm trying to write a statement to change the default value to 4. However, when I use the select * statement to double check, the column is still empty.
ALTER TABLE recipes
MODIFY NumberOfServings DEFAULT '4';
The DEFAULT value is used at INSERT time. It gives a default value to be inserted when you do not provide a value for the column in the INSERT statement.
You may want to update the table, so that all NULL values are replaced by a given value:
UPDATE recipes SET NumberOfServings=4 WHERE NumberOfServings IS NULL;
You can also specify a value to use when the column is NULL at QUERY time.
This can be done by using the NVL function:
SELECT NVL(NumberOfServings,4) FROM recipes;
http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions105.htm
The default value applies only when you insert new records into the table. It does not update any existing values in the table. Why do you enclose a numeric value in quotes?
why I am getting this error ?
In the table DDL I only have 2 columns , id (number) and name (varchar)
ALTER TABLE mytable ADD SUSPEND date NOT NULL
ORA-01758: table must be empty to add mandatory (NOT NULL) column
ORA-06512: at line 7
ORA-01758: table must be empty to add mandatory (NOT NULL) column ORA-06512: at line 7
And is your table empty? I think not.
There's probably a way around this involving adding the column as nullable, then populating every row with a non-NULL value, the altering the column to be not null.
Alternatively, since the problem is that these current rows will be given NULL as a default value, and the column is not allowed to be NULL, you can also get around it with a default value. From the Oracle docs:
However, a column with a NOT NULL constraint can be added to an existing table if you give a default value; otherwise, an exception is thrown when the ALTER TABLE statement is executed.
Here is a fiddle, how you could do it
Would a date in the future be acceptable as a temporary default? If so, this would work:
ALTER TABLE MYTABLE ADD (SUSPEND_DATE DATE DEFAULT(TO_DATE('21000101', 'YYYYMMDD'))
CONSTRAINT SUSPEND_DATE_NOT_NULL NOT NULL);
If table already contain the records then table won't allowes to add "Not null" column.
If you need same then set default value for the column or truncate the table then try.
I have that query :
INSERT INTO GOST (ASSORTMENTID, ROZMIAR, GOST)
VALUES ( 54,'S','MjgwMzktODkgMTc0LTk2')
I want insert new row in table GOST, but I don't want to specify column with primary key - GOSTID. I want that database set next id value.
When I run this code I have that error:
validation error for column GOSTID, value "* null *"
I understand that I should set GOSTID column in INSERT query, yes ?
It is possible to run this without this parameter ?
I think a sample script worths more than 1000 words:
Go to a shell interface in the firebird server machine, cd to a folder where you have read/write permissions, start isql or isql-fb (depends on your system and firebird version) and run this script:
create database 'netmajor.fdb' user 'sysdba' password 'masterkey';
set autoddl off;
create table netmajor_example (
netmajor_id integer not null
, str_data varchar(200)
, int_data integer
, constraint pk_netmajor_example
primary key (netmajor_id)
);
create generator netmajor_gen;
set term ^;
create trigger netmajor_pkassign
for netmajor_example
active before insert position 1
AS
begin
if (new.netmajor_id is null) then
new.netmajor_id = gen_id(netmajor_gen, 1);
end
^
commit work^
set term ; ^
insert into netmajor_example (str_data, int_data) values ('one', 1);
insert into netmajor_example (str_data, int_data) values ('twenty', 20);
commit work;
select * from netmajor_example;
Take a look at the results, which in my machine are:
; NETMAJOR_ID STR_DATA INT_DATA
;============ ============================ ============
; 1 one 1
; 2 twenty 20
IF you have questions, don't hesitate to contact. Best regards.
Obviously, your primary key is a NOT NULL column, which means, it's always required. You cannot insert a row without giving a value for the primary key (unless it were an "auto-number" column which gets automatically set by the database system).
Use "before insert" trigger to set value for primary key. Firebird doesn't have "auto-increment" field type, so you need take care of it by yourself.
See http://www.firebirdfaq.org/faq29/ for tutorial how to do this. Some DB applications (eg Database Workbench) can create the trigger and generator automatically.