unique-index

问题 When I run this query ALTER TABLE "dbo"."ROOM" DROP INDEX "UNIQUE"; I got this message: Error 1018: Incorrect syntax near 'INDEX'. If this is intended as a part of a table hint, A WITH keyword and parenthesis are now required. See SQL Server Books Online for proper syntax. The name of the unique index is, justly, UNIQUE . I think that is the problem, and it's an autogenerated name (for the SQL Server client that was used to create this index). This is the create table sentence: CREATE TABLE

问题 When I run this query ALTER TABLE "dbo"."ROOM" DROP INDEX "UNIQUE"; I got this message: Error 1018: Incorrect syntax near 'INDEX'. If this is intended as a part of a table hint, A WITH keyword and parenthesis are now required. See SQL Server Books Online for proper syntax. The name of the unique index is, justly, UNIQUE . I think that is the problem, and it's an autogenerated name (for the SQL Server client that was used to create this index). This is the create table sentence: CREATE TABLE

问题 I've tried to search through Mongo documentation, but can't really find any details on whether queries on unique indexes will be faster than queries on non-unique indexes (given the same data) So I understand that a unique index will have high selectivity and good performance. But, given two fields whose concatenation is unique, would a non-unique compound index perform slower than a unique compound index? I am assuming that unique indexes can slow down inserts as the uniqueness must be

问题 I have an error with arithmetic overflow inserting values into a lookup table with a row-id set as TINYINT datatype. This IS NOT a case where the number of unique records exceeds 255 values. This is a bit more unusual and did not occur during the first tests of this setup. The production version of the code below actually only has 66 unique values, but it is possible that new values could be added (slowly and in very small numbers) over time... 255 available slots should be more than enough

问题 I created a unique index (case description should be unique if IsDelete != 1) CREATE UNIQUE NONCLUSTERED INDEX [UniqueCaseDescription] ON [tblCases] ([fldCaseDescription] ASC) WHERE [IsDeleted] = CAST(0 AS varbinary(1)) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] Then when I run the following procedure it throws 'UPDATE failed because the following

问题 I want to create a unique id but uniqid() is giving something like '492607b0ee414' . What i would like is something similar to what tinyurl gives: '64k8ra' . The shorter, the better. The only requirements are that it should not have an obvious order and that it should look prettier than a seemingly random sequence of numbers. Letters are preferred over numbers and ideally it would not be mixed case. As the number of entries will not be that many (up to 10000 or so) the risk of collision isn't

问题 I have a table which has amongst many other fields one hstore db/schema.rb create_table "requests", force: true do |t| t.hstore "parameters" end Some of the records have a field parameters["company_id"] but not all of them. What I need to do is to make sure that only one Request object is created with a given parameters["company_id"] . There might be multiple attempts trying to save a record at the same time - thus the race condition. I am looking for unique company_id values inside the

问题 I am using Zend Framework 2 and I have created a User Entity. Now I am trying to make the username field unique. However the following error is coming up. [Semantical Error] The annotation "@UniqueEntity" in class User\Entity\User was never imported. Did you maybe forget to add a "use" statement for this annotation? I have added this code for uniqueness check @UniqueEntity("email") I can see that it is a method used in Symfony. How can I use it for Zend Framework 2? This is the Entity I am

问题 Why does INDEX creation statement have UNIQUE argument? As I understand, the non-clustered index contains a bookmark, a pointer to a row, which should be unique to distinguish even non-unique rows, so insuring non-clustered index to be unique ? Correct? So, do I understand that no-unique index can be only on clustered table? since "A clustered index on a view must be unique" [1] Since "The bottom, or leaf, level of the clustered index contains the actual data rows of the table" [1], do I

问题 Given the following schema: CREATE TABLE identifiers ( id TEXT PRIMARY KEY ); CREATE TABLE days ( day DATE PRIMARY KEY ); CREATE TABLE data ( id TEXT REFERENCES identifiers , day DATE REFERENCES days , values NUMERIC[] ); CREATE INDEX ON data (id, day); What is the best way to count all distinct days between two timestamps? I've tried the following two methods: EXPLAIN ANALYZE SELECT COUNT(DISTINCT day) FROM data WHERE day BETWEEN '2010-01-01' AND '2011-01-01'; QUERY PLAN --------------------