How to select the default values of a table? - sql-server

Question

In my app, when letting the user enter a new record, I want to preselect the database's default values.
Let's for example take this table:
CREATE TABLE pet (
ID INT NOT NULL,
name VARCHAR(255) DEFAULT 'noname',
age INT DEFAULT 1
)
I would like to do something like this:
SELECT DEFAULT VALUES FROM pet -- NOT WORKING
And it should return:
ID | name | age
--------------------
NULL | noname | 1
I would then let the user fill in the remaining fields, or let her change one of the defaults, before she clicks on "save".
How can I select the default values of a sql server table using tsql?

Answer 1

You don't "SELECT" the Default values, only insert them. A SELECT returns the rows from a table, you can't SELECT the DEFAULT VALUES as there's no such row inside the table.
You could do something silly, like use a TRANSACTION and roll it back, but as ID doesn't have a default value, and you don't define a value for it with DEFAULT VALUES, it'll fail in your scenario:
CREATE TABLE pet (
ID INT NOT NULL,
name VARCHAR(255) DEFAULT 'noname',
age INT DEFAULT 1
)
GO
BEGIN TRANSACTION;
INSERT INTO dbo.pet
OUTPUT inserted.*
DEFAULT VALUES;
ROLLBACK;
Msg 515, Level 16, State 2, Line 13
Cannot insert the value NULL into column 'ID', table 'Sandbox.dbo.pet'; column does not allow nulls. INSERT fails.
You can, therefore, just supply the values for your non-NULL columns:
BEGIN TRANSACTION;
INSERT INTO dbo.pet (ID)
OUTPUT inserted.*
VALUES(1);
ROLLBACK;
Which will output the "default" values:
ID|name |age
--|------|---
1|noname|1

Answer 2

Selecting the default values of all columns is not very straight-forward, and as Heinzi wrote in his comment - does require a level of permissions you normally don't want your users to have.
That being said, a simple workaround would be to insert a record, select it back and display to the user, let the user decide what they want to change (if anything) and then when they submit the record - update the record (or delete the previous record and insert a new one).
That would require you to have some indication if the record was actually reviewed and updated by the user, but that's easy enough to accomplish by simply adding a bit column and setting it to 1 when updating the data.

Answer 3

As I have commented before. There is no need for this query since you can press alt + f1 on any table in your editor in Management Studio and provide you every information you need for the table.
select sys1.name 'Name',replace(replace(
case
when object_definition(sys1.default_object_id) is null then 'No Default Value'
else object_definition(sys1.default_object_id)
end ,'(',''),')','') 'Default value',
information_schema.columns.data_type 'Data type'
from sys.columns as sys1
left join information_schema.columns on sys1.name = information_schema.columns.column_name
where
object_id = object_id('table_name')
and information_schema.columns.table_name = 'table_name'

Answer 4

It seems like this might be solution:
SELECT * FROM (
SELECT
sys1.name AS COLUMN_NAME,
replace(replace(object_definition(sys1.default_object_id),'(',''),')','') AS DEFAULT_VALUE
FROM sys.columns AS sys1
LEFT JOIN information_schema.columns ON sys1.name = information_schema.columns.column_name
WHERE object_id = object_id('pet')
AND information_schema.columns.table_name = 'pet'
) AS SourceTable PIVOT(MAX(DEFAULT_VALUE) FOR COLUMN_NAME IN(ID, name, age)) AS PivotTable;
It returns:
ID |name |age
----|------|---
NULL|noname|1
Probably the column types are incorrect - but maybe I can live with that.
Thanks for #Nissus to provide an intermediate step to this.