mysql

问题 I wanted to increment a number to a filename if the filename already exists in the database (based on the records too). for example if I add file with filename DOC it will check if DOC exist since DOC exist on the example below and the latest increment is 1 (DOC-1) then the filename would be DOC-2. If I add DOC again and the latest increment is 2 so the new filename would be DOC-3.so on and so forth. Any idea guys ? thank you. Sounds like what I want is to always create a new filename (by

问题 I need to execute a multiple MySql Queries and Multiple MongoDB queries. If the execution of one of the queries fails (SQL or Mongo) I must rollback all the executed queries. Is that possible? 回答1: You might want to check out Spring Transactions. This is one of the solutions I am aware of. Another solution might be to do it manually: store the current documents/rows try to update them and roll back if necessary. It might help to take a step back and ask yourself whether it really makes sense

问题 I'd like to select some data from my database using variables. Here is a short version of my code: // $a is either null or something like [1, 2] if ($a) { $debug = implode(',', $a); } else { $debug = [0-9]; } $sql = "SELECT id FROM user WHERE id IN ($debug)" How can I achieve that I get only user 1 and 2 (= value in $a ) if $a is set and all user if $a is not set? 回答1: First : be aware when you directly inject string inside queries, because you can be target of a SQL Injection Second : change

问题 I need to execute a multiple MySql Queries and Multiple MongoDB queries. If the execution of one of the queries fails (SQL or Mongo) I must rollback all the executed queries. Is that possible? 回答1: You might want to check out Spring Transactions. This is one of the solutions I am aware of. Another solution might be to do it manually: store the current documents/rows try to update them and roll back if necessary. It might help to take a step back and ask yourself whether it really makes sense

问题 Begin transaction Tx1 Tx1 performs a SELECT Commit Tx1 Begin transaction Tx2 in a different session, using a different connection Tx2 performs a SELECT Update rows in Tx2 Commit Tx2 Begin a new transaction, Tx1 Perform select - get results from step 2(??) Commit Tx1 Begin transaction Tx1 Perform select - get CORRECT results, i.e. the committed updates from Tx2 Very confused... How can this happen? It is happening reliably and consistently. 回答1: Turns out this can happen if the transaction

问题 Begin transaction Tx1 Tx1 performs a SELECT Commit Tx1 Begin transaction Tx2 in a different session, using a different connection Tx2 performs a SELECT Update rows in Tx2 Commit Tx2 Begin a new transaction, Tx1 Perform select - get results from step 2(??) Commit Tx1 Begin transaction Tx1 Perform select - get CORRECT results, i.e. the committed updates from Tx2 Very confused... How can this happen? It is happening reliably and consistently. 回答1: Turns out this can happen if the transaction

问题 I need to have bitmask in database. 64 bit is enough. Most use cases SELECT ... WHERE ... AND mask & value > 0 ... There are exist special datatype: BIT(64) for my case. But MySQL can make bit logical operations with BIGINT too. What I understand at this moment about BIT : Pros: Better visual representation 0b10010000 better 144 (but I can make CONV(144,10,2) with integer and get same representation) Cons: Worse support of type (I had some problem in golang, and wrote own type to work with it

问题 After migrating from .NET Core 2.x to .NET Core 5.0, we are facing this problem. Error: (Added as a CODE for better readability) The LINQ expression 'OUTER APPLY Projection Mapping: ( SELECT e0.Id, e0.FirstName, e0.MiddleName, e0.LastName FROM Employees AS e0 WHERE (((e0.Status != 4) && EXISTS ( Projection Mapping: SELECT 1 FROM FunctionRoles AS f0 WHERE t.Id == f0.SchoolId)) && (e0.FunctionRoleId == (Projection Mapping: EmptyProjectionMember -> 0 SELECT TOP(1) f1.Id FROM FunctionRoles AS f1

问题 I'm working on a distributed system that uses distributed transactions, which means that I may have a transaction that needs to edit multiple databases (on multiple servers) at the same time. In my system there is a controller to manage the distribution. the scenario that I want to satisfy is: server A wants to initiate a distributed transaction. the participants are server A and server B. so server A sends a request to the controller to initiate a distributed transaction. the controller

问题 I'm working on a distributed system that uses distributed transactions, which means that I may have a transaction that needs to edit multiple databases (on multiple servers) at the same time. In my system there is a controller to manage the distribution. the scenario that I want to satisfy is: server A wants to initiate a distributed transaction. the participants are server A and server B. so server A sends a request to the controller to initiate a distributed transaction. the controller