You use a self join when a table references data in itself. E.g., an Employee table may have a SupervisorID column that points to the employee that is the boss of the current employee. To query the data and get information for both people in one row, you could self join like this:
If you found the exact error “The wait operation timed out” then it is likely you have a database call that took longer than expected. This could be due to any number of things: Transient network problem High SQL server load Problem with SAN, RAID, or storage device Deadlock or other form of multiprocess contention … Read more
You can do the following (I guessed on table fields,etc) Based on your request for multiple halls you could do it this way. You just join on your Hall table multiple times for each room pref id:
Try using different quotes for “y” as the identifier quote character is the backtick (“`”). Otherwise MySQL “thinks” that you point to a column named “y”. See also MySQL 5 Documentation
Try using different quotes for “y” as the identifier quote character is the backtick (“`”). Otherwise MySQL “thinks” that you point to a column named “y”. See also MySQL 5 Documentation
The SQL WITH clause was introduced by Oracle in the Oracle 9i release 2 database. The SQL WITH clause allows you to give a sub-query block a name (a process also called sub-query refactoring), which can be referenced in several places within the main SQL query. The name assigned to the sub-query is treated as … Read more
Your problem is those pernicious double quotes. Oracle SQL allows us to ignore the case of database object names provided we either create them with names all in upper case, or without using double quotes. If we use mixed case or lower case in the script and wrapped the identifiers in double quotes we are … Read more
An nvarchar column can store any Unicode data. A varchar column is restricted to an 8-bit codepage. Some people think that varchar should be used because it takes up less space. I believe this is not the correct answer. Codepage incompatabilities are a pain, and Unicode is the cure for codepage problems. With cheap disk … Read more
Stored procedures are a batch of SQL statements that can be executed in a couple of ways. Most major DBMs support stored procedures; however, not all do. You will need to verify with your particular DBMS help documentation for specifics. As I am most familiar with SQL Server I will use that as my samples. … Read more
I have an SQL statement that has a CASE from SELECT and I just can’t get it right. Can you guys show me an example of CASE where the cases are the conditions and the results are from the cases. For example: where the results show