That means even in the presence of a unique constraint it is possible to store duplicate rows that contain a null value in at least one of the constrained columns. When the WHERE clause is present, a partial index is created.A partial index is an index that contains entries for only a portion of a table, usually a portion that is more useful for indexing than the rest of the table.The table has four fields with data types of decimal that I need to convert to double data types once I’ve written the Is it possible to alter multiple columns in one statement in MS SQL?I am trying to add default values to a group of columns, but I get a syntax error when I combine them all into one statement like this: ALTER TABLE drawinglist ADD CONSTRAINT ISOKEYPLAN_DWGTITLEPREFIX SQL Alter: add multiple FKs?ALTER TABLE dbo.doc_exb DROP COLUMN column_b ; GO -- Remove multiple columns.
Transaction History Archive WITH NOCHECK ADD CONSTRAINT PK_Transaction History Archive_Transaction ID PRIMARY KEY CLUSTERED (Transaction ID) WITH (FILLFACTOR = 75, ONLINE = ON, PAD_INDEX = ON); GO CREATE TABLE dbo.doc_exb (column_a INT ,column_b VARCHAR(20) NULL ,column_c datetime ,column_d int) ; GO -- Remove a single column.Contact Backup DROP CONSTRAINT FK_Contact Bacup_Contact ; GO DROP TABLE Person.Contact Backup ; IF OBJECT_ID ( 'dbo.doc_exy', 'U' ) IS NOT NULL DROP TABLE dbo.doc_exy; GO -- Create a two-column table with a unique index on the varchar column.Remove two constraints and one column -- The keyword CONSTRAINT is optional. ALTER TABLE dbo.doc_exc DROP CONSTRAINT CONSTRAINT my_constraint, my_pk_constraint, COLUMN column_b ; GO CREATE TABLE Person.Contact Backup (Contact ID int) ; GO ALTER TABLE Person.I think part of the confusion (yours and mine) is that UNIQUE is both a constraint and an index.You can include a WHERE when you create it as an index but not when you create it as a constraint. column_c INT NULL CONSTRAINT column_c_fk REFERENCES doc_exe(column_a), -- Add a column with a constraint to enforce that -- nonnull data is in a valid telephone number format.column_d VARCHAR(16) NULL CONSTRAINT column_d_chk CHECK (column_d LIKE '[0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]' OR column_d LIKE '([0-9][0-9][0-9]) [0-9][0-9][0-9]-[0-9][0-9][0-9][0-9]'), -- Add a nonnull column with a default.In general, a unique constraint is violated when there is more than one row in the table where the values of all of the columns included in the constraint are equal.However, two null values are not considered equal in this comparison.[...] Another possible application is to use WHERE with UNIQUE to enforce uniqueness over a subset of a table. So if your intent is too limit the uniqueness to non-NULL values then you don't need your partial index; but, if you just want to avoid indexing NULL values then you could do it through CREATE INDEX (but not ALTER TABLE).I don't know if leaving NULLs out of your index would have any noticeable effect though.CREATE TABLE dbo.doc_exz ( column_a INT, column_b INT) ; GO INSERT INTO dbo.doc_exz (column_a)VALUES ( 7 ) ; GO ALTER TABLE dbo.doc_exz ADD CONSTRAINT col_b_def DEFAULT 50 FOR column_b ; GO INSERT INTO dbo.doc_exz (column_a) VALUES ( 10 ) ; GO SELECT * FROM dbo.doc_exz ; GO DROP TABLE dbo.doc_exz ; GO CREATE TABLE dbo.doc_exe ( column_a INT CONSTRAINT column_a_un UNIQUE) ; GO ALTER TABLE dbo.doc_exe ADD -- Add a PRIMARY KEY identity column.