unique-key

I need to remove a unique key from my mysql table. How can remove that using mysql query. I tried this but it is not working alter table tbl_quiz_attempt_master drop unique key; Please help me Thanks All keys are named, you should use something like this - ALTER TABLE tbl_quiz_attempt_master DROP INDEX index_name; To drop primary key use this one - ALTER TABLE tbl_quiz_attempt_master DROP INDEX `PRIMARY`; ALTER TABLE Syntax . Narendran Parivallal First you need to know the exact name of the INDEX (Unique key in this case) to delete or update it. INDEX names are usually same as column names. In

Possible Duplicate: The proper way to implement unique constraint that allows multiple NULL values in SQL Server I have a column in my table where all the values must either be unique, or NULL. I tried adding a Unique Key to the table for this column, but this seems to mean I can only have 1 NULL value? How can I set a constraint so that all the values are unique, unless they are NULL? SQL Server 2008 has filtered indexes that allow this but they are not available in 2005. In SQL Server 2005 you can create an indexed view with definition CREATE VIEW dbo.Foo WITH SCHEMABINDING AS SELECT bar

Using Schema First , I have a database structure, as so ExternalDataItems --- edataitem_id PK -- surrogate auto-increment - NOT for FK relation here datahash UX -- Candidate Key / Unique Index (binary(20)) ExternalMaps --- emap_id PK ext_datahash FK on ExternalDataItems.datahash - NOT referencing the surrogate PK and after generating the SSDL/CSDL 1 has this <Association Name="FK_ExtMaps_ExtDataItems"> <End Multiplicity="1" Role="ExternalDataItems" Type="Store.ExternalDataItems" /> <End Multiplicity="*" Role="ExternalMaps" Type="Store.ExternalMaps" /> <ReferentialConstraint> <!-- error on this

I want to retrieve the unique ID of a machine. Like others I also did a lot of research, and found none of the process of Unique ID generation works perfectly. For Motherboard Serial Number (ID): It is Unique; it can't be changed. However, it may not be found in some machines if Manufacturers didn't put information on Memory Location. Then I found it gives no Unique Id .. lol Similarly for "Processor ID", "BIOS ID". Afraid to use other hardware information of PC. MAC and Windows Product ID can be changed by a software. And is "Windows Product ID" unique? One option is there to combine those

I was told by a friend: What unique key do you use? I hope you are not saving the entire user name --- this will use up too much table space! Assign an unique userID to each (unique) userNAME and save this userID (should be INTEGER UNSIGNED auto_increment or BIGINT UNSIGNED auto_increment). Don't forget to create a reference FOREIGN KEY ( userID ) REFERENCES usertable ( userID ) in all tables using the userID. Is the above statement correct? Why or why not? I think he is right ( for the wrong reason) because primary key cannot change, but username can change. So you should use userid because

I'm trying to create a relation where any of four different parts may be included, but any collection of the same parts should be handled as unique. Example: An assignment must have an assigned company, may optionally have an assigned location, workgroup and program. An assignment may not have a workgroup without a location. Let's assume we have companies A, B, C; locations X, Y, Z; workgroups I, J, K and programs 1, 2, 3. So valid relations could include A - X - I - 1 A - Z - 2 B - Y C C - 3 B - Z - K But invalid relations would include A - K (Workgroup without location) Y - K - 1 (No company