unique

问题 I am trying to migrate an Oracle merge query to PostgreSql. As described in this article, Postgres UPSERT syntax supports a "where clause" to identify conditions of conflict. Unfortunately, that webpage does not provide an example with the "where clause". I tried searching for it elsewhere but could not find it. Hence this question. Following the same example in the above given webpage, here is an example setup: CREATE TABLE customers ( customer_id serial PRIMARY KEY, name VARCHAR UNIQUE,

问题 I'm using dlopen / dlclose to load lib with glibc 2.21. Is there a C++ call to check a lib as a DF_1_NODELETE flag set ? readelf seems to be able to do it. or at least if a lib has unique symbol defined in it ? nm is definitely able to do it. ideally i would like something like : CloseLib( libHandle lib) { if( checkIfLibIsClosable(lib) ) { dlclose(lib) } } This is in order to avoid calling dlclose on lib with DF_1_NODELETE flag, as calling it will fails with an assert error : Inconsistency

问题 I'm using dlopen / dlclose to load lib with glibc 2.21. Is there a C++ call to check a lib as a DF_1_NODELETE flag set ? readelf seems to be able to do it. or at least if a lib has unique symbol defined in it ? nm is definitely able to do it. ideally i would like something like : CloseLib( libHandle lib) { if( checkIfLibIsClosable(lib) ) { dlclose(lib) } } This is in order to avoid calling dlclose on lib with DF_1_NODELETE flag, as calling it will fails with an assert error : Inconsistency

问题 I've created a salt using; md5(rand(0,10000000)); (there is probably a better way?) There doesn't seem to be possible to make a text field unique in MYSQL. So how do I check if the salt has already been used for a previous user? Or should I generate the salt based on the current date/time? as it is impossible for 2 users to register at exactly the same time correct? 回答1: For a salt, uniqueness is more important than length and predictability. You assume the attacker has the salt. A

问题 I write websocket chat. How to generate unique id for user? now i use this code: id = new DateTime.now().millisecondsSinceEpoch; is there any more neat solution? 回答1: 1. There is a UUID pub package: http://pub.dartlang.org/packages/uuid example usage: // Generate a v1 (time-based) id uuid.v1(); // -> '6c84fb90-12c4-11e1-840d-7b25c5ee775a' // Generate a v4 (random) id uuid.v4(); // -> '110ec58a-a0f2-4ac4-8393-c866d813b8d1' // Generate a v5 (namespace-name-sha1-based) id uuid.v5(uuid.NAMESPACE

问题 Are indices (indexes) defined as UNIQUE case sensitive in MySQL? 回答1: It depends on the collation of the field - if it's ci (case insensitive) or cs (case sensitive). The unique index would apply accordingly. 回答2: You can make a column case-sensitive by using this syntaxis. the unique index also will be case-sensitive. ALTER TABLE tbl_name MODIFY col_name column_definition [CHARACTER SET charset_name] [COLLATE collation_name] Example: ALTER TABLE `tablename` MODIFY `column` VARCHAR(100)

问题 Are indices (indexes) defined as UNIQUE case sensitive in MySQL? 回答1: It depends on the collation of the field - if it's ci (case insensitive) or cs (case sensitive). The unique index would apply accordingly. 回答2: You can make a column case-sensitive by using this syntaxis. the unique index also will be case-sensitive. ALTER TABLE tbl_name MODIFY col_name column_definition [CHARACTER SET charset_name] [COLLATE collation_name] Example: ALTER TABLE `tablename` MODIFY `column` VARCHAR(100)

问题 I got a very common question when I was using Spring JDBCTemplate, I want to get the ID value after I inserted a new data record into database, this ID value will be referred to another related table. I tried the following way to insert it, but I always return 1 rather than its real unique ID. (I use MySQL as the database) public int insert(BasicModel entity) { String insertIntoSql = QueryUtil.getInsertIntoSqlStatement(entity); log.info("SQL Statement for inserting into: " + insertIntoSql);

问题 I got a very common question when I was using Spring JDBCTemplate, I want to get the ID value after I inserted a new data record into database, this ID value will be referred to another related table. I tried the following way to insert it, but I always return 1 rather than its real unique ID. (I use MySQL as the database) public int insert(BasicModel entity) { String insertIntoSql = QueryUtil.getInsertIntoSqlStatement(entity); log.info("SQL Statement for inserting into: " + insertIntoSql);

问题 I have an object with a String that holds a unique id . (such as "ocx7gf" or "67hfs8") I need to supply it an implementation of int hascode() which will be unique obviously. how do i cast a string to a unique int in the easiest/fastest way? 10x. Edit - OK. I already know that String.hashcode is possible. But it is not recommended in any place. Actually' if any other method is not recommended - Should I use it or not if I have my object in a collection and I need the hashcode. should I concat