sql if exists return true

Summary:Exists (the result set returned by SQL is true) not exists (the result set returned by SQL is true) is as follows: Table A ID name 1 A1 2 A2 Exists (the result set returned by SQL is true)Not exists (SQL does not return true result sets)As

Transferred from Https://www.cnblogs.com/liyasong/p/sql_in_exists.html and http://blog.csdn.net/lick4050312/article/details/4476333Table ShowThe two tables involved in the query, a user and an order table, are the following:User table:　　　　Order

For example, there is a query in the Northwind database thatSELECT C.customerid,companyname from Customers CWHERE EXISTS (SELECT OrderID from Orders o WHERE o.customerid=c.customerid)How does this exists work? The subquery returns the OrderID field,

SQL query in the in, exists, not in, not exists usage and difference, sqlexists 1. in and exists In connects the External table to the internal table as a hash (Dictionary set), while exists loops the External table and queries the internal table

Usage and difference of in, exists, not in, and not exists in SQL queries 1. in and exists In connects the External table to the internal table as a hash (Dictionary set), while exists loops the External table and queries the internal table after

Content from online:53090467The data of the main query is placed in the subquery for conditional validation, depending on the validation result (TRUE or FALSE) to determine whether the data results of the main query are retained.Here's an example of

Source of the blog post (exists and not EXISTS usage in Oracle): http://chenshuai365-163-com.iteye.com/blog/1003247Bowen Source (in VS. exists statement efficiency issues): http://www.cnblogs.com/iceword/archive/2011/02/15/1955337.htmlAexists (SQL

exists summary of database SQL statements SQL exists in learningFirst to compare the following syntax:--deals= Trading tables, areas= regional tables, such as Hong Kong; Our purpose: To view the regions with transactionsSELECT * from areas where ID

EXISTS (SQL returns the result set as true)Not EXISTS (SQL does not return result set is true)As follows:Table AID NAME1 A12 A23 A3Table BID AID NAME1 1 B12 2 B23 2 B3Table A and table B are 1-to-many relationships a.id = B.aidSelect Id,name from A

Text: The exists in the SQL drip 35-sql statementFor example, in the Northwind database there is a query for select C.customerid,companyname from Customers C where EXISTS (select OrderID from Orders o where O . Customerid=c.customerid) How does this