Db2 Create Unique Index

[Olowookere Devost]

Thistopic describes how to create a unique index on a table in SQL Server by using SQL Server Management Studio or Transact-SQL. A unique index guarantees that the index key contains no duplicate values and therefore every row in the table is in some way unique. There are no significant differences between creating a UNIQUE constraint and creating a unique index that is independent of a constraint. Data validation occurs in the same manner, and the query optimizer does not differentiate between a unique index created by a constraint or manually created. However, creating a UNIQUE constraint on the column makes the objective of the index clear. For more information on UNIQUE constraints, see Unique Constraints and Check Constraints.

When you create a unique index, you can set an option to ignore duplicate keys. If this option is set to Yes and you attempt to create duplicate keys by adding data that affects multiple rows (with the INSERT statement), the row containing a duplicate is not added. If it is set to No, the entire insert operation fails and all the data is rolled back.

You cannot create a unique index on a single column if that column contains NULL in more than one row. Similarly, you cannot create a unique index on multiple columns if the combination of columns contains NULL in more than one row. These are treated as duplicate values for indexing purposes.

Multicolumn unique indexes guarantee that each combination of values in the index key is unique. For example, if a unique index is created on a combination of LastName, FirstName, and MiddleName columns, no two rows in the table could have the same combination of values for these columns.

When you create a PRIMARY KEY constraint, a unique clustered index on the column or columns is automatically created if a clustered index on the table does not already exist and you do not specify a unique nonclustered index. The primary key column cannot allow NULL values.

When you create a UNIQUE constraint, a unique nonclustered index is created to enforce a UNIQUE constraint by default. You can specify a unique clustered index if a clustered index on the table does not already exist.

To create an indexed view, a unique clustered index is defined on one or more view columns. The view is executed and the result set is stored in the leaf level of the index in the same way table data is stored in a clustered index. For more information, see Create Indexed Views.

Requires ALTER permission on the table or view. User must be a member of the sysadmin fixed server role or the db_ddladmin and db_owner fixed database roles.

In the Index Columns dialog box, under Column Name, select the columns you want to index. You can select up to 16 columns. For optimal performance, select only one or two columns per index. For each column you select, indicate whether the index arranges values of this column in ascending or descending order.

Optional: In the main grid, under Table Designer, select Ignore Duplicate Keys and then choose Yes from the list. Do this if you want to ignore attempts to add data that would create a duplicate key in the unique index.

Note: Updating a table with indexes takes more time than updating a table without (because the indexes also need an update).So, only create indexes on columns that will be frequently searched against.

So this is where we decided to take a couple of steps back. Could we just get the forums up and running again and put it in read only mode while we figure out this backup business. We managed to do this by fixing some permission issues for both postgres and redis and the forums got back up online on the old version. Not everything works, ie going to admin -> user -> groups gets us this error:

So we started a new EC2 instance, run the discourse_docker getting started instructions and started our import. Then we run into a weird issue: it could not create an index because the data did not match the uniqueness requirements of the index:

Once all indexes worked, we were able to make a backup and import it correctly in the new instance. Migrations ran as expected, we swapped instances and we got up and running Cheers to the resilience of Discourse

One last tip for people debugging data corruption issues. Initially when our import failed on duplicate data I jumped into the Rails console and searched by the data that caused the index to fail to be created.

However, by querying using the indexed fields, Postgres was using the broken index to generate the results! So my initial query showed 1 result, and later when deleting that entry it showed 0 results.

So I then follow the advice here Tool Reference 003340 , but the add unique index radio button isnt honored. This happens on newly created file geodatabase and existing ones as well.

Anyone else seeing this behavior? I submitted a ticket to tech support.

Yes, I'm glad @JacobMouw found this post for me because I didn't realize my Global ID attribute index was not unique, since I was checking the box for it. I've been very frustrated that the Append Tool fails when using the preserve Global ID's environment setting.

I've been taking data from ArcGIS Online, working with it offline in a file geodatabase to clean it up, load data, make structure changes, etc. and re-publish, and thus I want to preserve my Global ID's to maintain continuity between the datasets. I've had the issue multiple times now.

I thought that it did have a unique attribute index on the Global ID field because when I run the attribute index gp tool, it runs successfully, and I don't get a warning that the index is not unique.

I would like the ability to have a unique index on a Global ID field on a file geodatabase so that I can append data from feature class to feature class and maintain global id's. This helps us keep historical records. We are not allowed access to the enterprise environment in our organization for this work and it's impractical to do all of our work online with feature layers.

I'm having the EXACT same issue. I want to be able to download data from AGO, clean it up and load into a new template file GDB, then publish new hosted feature layers. I can do workarounds, but a file GDB should be able to handle this so I can do offline cleanup/reorganization.

When an index is declared unique, multiple table rows with equal indexed values are not allowed. By default, null values in a unique column are not considered equal, allowing multiple nulls in the column. The NULLS NOT DISTINCT option modifies this and causes the index to treat nulls as equal. A multicolumn unique index will only reject cases where all indexed columns are equal in multiple rows.

PostgreSQL automatically creates a unique index when a unique constraint or primary key is defined for a table. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the mechanism that enforces the constraint.

If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.

I get a duplicate index error trying to replicate your problem, involving the primary key, but not the specific error you describe. Does the table already have data in it? Are you using an unsigned integer? I think Base has trouble with unsigned. Are you creating a primary key? Please describe the exact sequence of inputs, as on my setup it repeatedly prompts for saves; do you save? Finally, what version of LO.

I tried to replicate the error in a brand new database and there was no error. But I need to work with this particular database. As I mentioned in my edited post, it was created as a result of connecting accdb database. So, maybe this is a problem. I noticed for example, that available data types are different in this database and in the new database (e.g. Integer [Long] instead of Integer [INTEGER]).

The link you reference offers three different ways to connect. Consider trying the other ways, ADO and ODBC. Your problem rhymes the the one I encountered using a MySQL backend, where Base or connectors failed to recognize the extended range of UNSIGNED integers, meaning the -x to 0 range that should have been added to the normal signed range. If it helps here is that discussion.

I disagree. I stated that I can create a new table in an Access database connected to Base, create a Primary Key and enter data in the Access database. The difference is that I am using LO 4.4.1.2 whereas @aloe is using LO 4.4.4.3.

That said, I suspect that Access would sneak in a primary key when done through ythat system and even though this command will add a UNIQUE constraint successfully, it will not allow you to enter new data through the Base front-end, which peterwt also appears to confirm is a limitation of the Base interface, although a mild one considering that adding a PRIMARY key is easy to do.

I have a table in Postgres with records of type [event_id, user_id, status]. The user is scoped per event, so I have a unique index on [event_id, user_id] so that a user has a unique status. The status is an enum type.

Ok thanks for the information. On your database before the migration, could you verify that the table live_measures contain a unique index named live_measures_component on the columns component_uuid & metric_id ?

You can use a unique index on a hypertable to enforce constraints. You do notneed to have a unique index on your hypertables. When you create a unique index,it must contain all the partitioning columns of the hypertable.

This article provides two different options for creating a u","articleBody":"How to create unique index for a field of a table

DescriptionThis article provides two different options for creating a unique index for a field of a table. See below for additional information and steps to follow.

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