pg_dumpall -g now only dumps role- and tablespace-related attributes. Now pg_dump -create and pg_restore -create will restore these database properties in addition to the objects within the database. Previously, attributes of the database itself, such as database-level GRANT/ REVOKE permissions and ALTER DATABASE SET variable settings, were only dumped by pg_dumpall. We have created a column on a table, which holds UNIQUE values and also multiple NULL values using Primary key values, computed column and UNIQUE constraint on the computed column.Make pg_dump dump the properties of a database, not just its contents (Haribabu Kommi) Now let’s try to insert another row without Social Security Number as shown below.
Now try to insert one row without Social Security Number: Insert into Emp (, Let’s try to insert some data as shown below. Now let’s add the UNIQUE constraint to the computed column: Alter table Emp Add constraint ssn_unique UNIQUE ( ) Is NULL then convert(varchar(12),) else end Let’s create the computed column for Social Security Number as shown below. If the Social Security Number column is a varchar column then we can create the computed column and the constraint as shown below in order to achieve the same goal of having unqiueness with multiple NULL values. Try to insert another row without Social Security Number: Insert into Emp (, Let’s try to insert one row without Social Security Number as shown below. Alter table Emp Add constraint ssn_unique UNIQUE ( ) Now let us add the UNIQUE constraint to the computed column as shown below. USE Īlter table Emp Add MySSN as case when Now let us recreate the database from the scratch, only this time we will add a computed column as shown below. This can be achieved using a computed column and adding a contraint to the computed column instead of on the actual Social Security Number column. We want the column to accept unique values and also accept multiple NULL values. However, that is not the behaviour we want for this column. It allows one row of data with NULL values. This is the normal behaviour of UNIQUE constrain on a NULL column. Violation of UNIQUE KEY constraint ‘ssn_unique’.Ĭannot insert duplicate key in object ‘dbo.Emp’. Now let us try to insert another row without Social Security Number as shown below. Now let us try to insert one row without Social Security Number as shown below. However, in situations of people entering this country using a work visa, it would take sometime for them to get a social security number. Values(4,’Sonia’,’Keira’,’Sony’,131413426)Īs we know, social security number is unique.
Now let us try to insert some data as shown below. Alter table Emp Add constraint ssn_unique UNIQUE We know social security number is unique, so let us add UNIQUE constraint to the column. ( int not NULL constraint Emp_pk primary key clustered, IF EXISTS (SELECT name FROM sys.databases WHERE name = N’Employee’) Let us assume that we have a database, MyDB, and we want to create a table that holds social security numbers, as shown below.
Postgresql alter table allow null how to#
In this article, I am going to illustrate how to maintain uniqueness on a column and also allow multiple NULL values. However, there are situations when we need more than one NULL value in the column but still have to maintain uniqueness, ignoring all those NULL values. As you know, when you create a UNIQUE constraint on a nullable column, SQL Server allows only one NULL value, thereby maintaining the UNIQUEness.
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