sql

问题 I'm having trouble with slow delete queries. I have a schema ,say "target" containing tables that all have an equivalent table (identical columns & primary keys) in another one, say "delta". I now want to delete all rows that appear in the delta schema from the target schema. I have tried this using the DELETE FROM WHERE EXISTS approach, but that seems incredibly slow. Here's an example query: DELETE FROM "target".name2phoneme WHERE EXISTS( SELECT 1 FROM delta.name2phoneme d WHERE

问题 How can I replace D:\temp\test.xls with filePath in OleDbConnection statement. I can get the exactly filePath (with OpenFileDialog, then I can located my .xls file conveniently, no more hardcoded), but when I insert the variable filePath as Style2, it doesn't work. How can I fix this ? Thanks. Style1 OleDbConnection dbConnection = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\temp\test.xls;Extended Properties=""Excel 8.0;HDR=Yes;"""); Style2 OleDbConnection

问题 This question already has answers here : SQL select only rows with max value on a column [duplicate] (27 answers) Closed 7 months ago . Suppose having query SELECT c_id, id, max(date) as max_date FROM table GROUP BY c_id,updated And following result: c_id, id, max_date 1 5 2017-12-28 16:09:20 1 6 2019-12-28 16:09:20 2 7 2017-12-28 16:09:20 2 8 2019-12-28 16:09:20 I expect to get: c_id, id, max_date 1 6 2019-12-28 16:09:20 2 8 2019-12-28 16:09:20 How to achieve that in mysql 5.7? 回答1: Use a

问题 This question already has answers here : SQL select only rows with max value on a column [duplicate] (27 answers) Closed 7 months ago . Suppose having query SELECT c_id, id, max(date) as max_date FROM table GROUP BY c_id,updated And following result: c_id, id, max_date 1 5 2017-12-28 16:09:20 1 6 2019-12-28 16:09:20 2 7 2017-12-28 16:09:20 2 8 2019-12-28 16:09:20 I expect to get: c_id, id, max_date 1 6 2019-12-28 16:09:20 2 8 2019-12-28 16:09:20 How to achieve that in mysql 5.7? 回答1: Use a

问题 I have SQL Server Database which is present on some web server.I made a WPF or Windows form Desktop application using C# .Net.I want to retrieve data from sql server database in my desktop application as per end user requirements on its own local PC.Give me best way and best solution regarding security and accessing data. 回答1: You have 2 options. 1. Write the business logic layer which resides on the web-server and communicates with DB to serve the required data based on requests coming from

问题 I have SQL Server Database which is present on some web server.I made a WPF or Windows form Desktop application using C# .Net.I want to retrieve data from sql server database in my desktop application as per end user requirements on its own local PC.Give me best way and best solution regarding security and accessing data. 回答1: You have 2 options. 1. Write the business logic layer which resides on the web-server and communicates with DB to serve the required data based on requests coming from

问题 I would like to get and provide the total total_record_count, page_number, page_size, total_pages, has_more information in the response and being able to paginate through the result since I LIMIT the query to 100. What's the best way to do this? That's my current setup: router.get('/?', function(req, res, next) { const sql = "SELECT * from users "; const existingParams = ["title", "active"].filter(field => req.query[field]); if (existingParams.length) { sql += " WHERE "; sql += existingParams

问题 I would like to get and provide the total total_record_count, page_number, page_size, total_pages, has_more information in the response and being able to paginate through the result since I LIMIT the query to 100. What's the best way to do this? That's my current setup: router.get('/?', function(req, res, next) { const sql = "SELECT * from users "; const existingParams = ["title", "active"].filter(field => req.query[field]); if (existingParams.length) { sql += " WHERE "; sql += existingParams

问题 I want to notify users of changes on a site. Users are subscribed to different kinds of changes so I don't send all changes to all users. Here's what I am thinking: at t=0 (i.e. an if statement that checks that some table is empty) I basically have an SQL query that fetches the appropriate changes and mails to the appropriate users. I then populate a user_changes table which essentially stores what changes have been mailed to what users. Mailing is done with the php mail function Then at t>0

问题 I have a requirement like below. There are 70 tables and I have to build 70 queries from those 70 different tables depending on some condition. Let us say the table names are TAB_1,TAB_2,TAB_3.....,TAB_70 .The number of columns and data type of the columns are different in each table. I will get user input and I have to pass that value to an Oracle PL/SQL function or procedure GET_RESULT() and get the output in tabular format(same as we get when we run a query). Also, I have to show the