unique

问题 I want to know whether is it a good idea to catch exception based on unique index of sql in java. i want to catch an exception like 'duplicate entry for 1-0' if so then handle exception otherwise insert properly in database table? 回答1: I say you don't do that, for two reasons: the error messages are a bit unclear: ERROR 1062 (23000): Duplicate entry 'xxx' for key 1 . Are you always 100% sure which key is 1? it locks in you to a specific database vendor I find it simpler to transactionally :

问题 I am working through an iOS swift Tetris tutorial* and have it completed and working. But I am puzzled about one particular aspect - the Hashable protocol. The function: class Block: Hashable, Printable { [...] var hashValue: Int { return self.column ^ self.row } Rows go 0..9, and Columns 0..20. The notes says of this function "We return the exclusive-or of our row and column properties to generate a unique integer for each Block.". But my understanding is that 0^1 would be the same as 1^0,

问题 I want to make unique constraint in cassandra . As i want to all the value in my column be unique in my column family ex: name-rahul phone-123 address-abc now i want that i this row no values equal to rahul ,123 and abc get inserted again on seraching on datastax i found that i can achieve it by doing query on partition key as IF NOT EXIST ,but not getting the solution for getting all the 3 values uniques means if name- jacob phone-123 address-qwe this should also be not inserted into my

问题 I have a sqlite table: for example CREATE TABLE TEST (id integer primary key, number integer unique, name text); However, i need to make REPLACE without autoincrementing the id field when it updates. For example : THE TABLE IS EMPTY REPLACE INTO TEST (null, 23, 'Bill'); REPLACE INTO TEST (null, 52, 'Jack'); When I execute the query, SELECT * FROM TEST; I get... 1|23|Bill 2|52|Jack if I do... REPLACE INTO TEST VALUES (null, 52, 'John'); from the query SELECT * FROM TEST; i get.. 1|23|Bill 3|52

问题 In this code, I have an Entity Framework 4 model with a single "Thing" entity that has an Id and a Name(string) column. I would like to ensure that when I call FindOrCreateThing(name) from multiple threads, only one row in the Things table will ever be created with the given name. Currently, I'm using locks to accomplish this, and it seems to work... but, what are some better ways? How is this common scenario handled in other projects? Thanks! class Program { private static string[] names =

问题 You guys are amazing. I've posted here twice in the past couple of days - a new user - and I've been blown away by the help. So, I figured I'd take the slowest query I've got in my software and see if anyone can help me speed it up. I use this query as a view, so it's important that it be fast (and it isn't!). First, I have a Contacts Table that store my company's customers. In the table is a JobTitle column which contains an ID which is defined in the Contacts_Def_JobFunctions table. There

问题 I am facing a problem on how to set a new column to unique using Oracle 11g. I try to use this code but it getting error: ALTER TABLE QAS_ASSIGNED_STATE ADD UNIQUE (cuid); 回答1: You should define column's type. Like this: alter table QAS_ASSIGNED_STATE add cuid number NULL; and then add constraint: ALTER TABLE QAS_ASSIGNED_STATE ADD CONSTRAINT constraint_cuid UNIQUE (cuid ); 来源： https://stackoverflow.com/questions/36030261/oracle-11g-add-new-column-and-set-as-unique

问题 So i'm practicing some sql coding for a test and I can't get a foreign key to reference a primary key. Here's the table that doesn't work: CREATE TABLE ASSIGNMENT( ASSIGN_ID NUMBER(2) NOT NULL, START_DATE DATE, END_DATE DATE, BUDGET NUMBER (10,2), MANAGER_ID NUMBER(2), PRIMARY KEY (ASSIGN_ID,MANAGER_ID), FOREIGN KEY (MANAGER_ID) REFERENCES EMPLOYEE(EMP_ID) ); Here's the table it is referencing: CREATE TABLE EMPLOYEE( EMP_ID NUMBER(2) NOT NULL, NAME VARCHAR(40), OFFICE VARCHAR(20), EXPERT_ID

问题 in my mysql table I made look like this one ControlNum|Title |NumOfEpis|Description| 001 |naruto |500 |some text | 002 |conan |700 |some text | now I made a user control in C# where in the user is allowed to update all columns except the primary"ControlNum". so assuming each column has its own textboxes in that said user control so in order to avoid duplication in the title column like for example if the user edit the row 2 title and put it "naruto" also it would be duplicated..so I create

问题 I am working with a multi-dimensional array. How can I remove duplicates by value? In the following array, [0], [2] and [5] have the same [ID]. Is there a function that will remove any duplicate arrays based on a particular value? In this case, I would like to remove array [2] and array [5], as they have the same [ID] as array [0]. Thank you for any information you may have. Array ( [0] => stdClass Object ( [d] => 2010-10-18 03:30:04 [ID] => 9 ) [1] => stdClass Object ( [d] => 2010-10-18 03