SQL Inner-join with 3 tables?
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:
SQL
Unknown column in ‘field list’ error on MySQL Update query
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
Unknown column in ‘field list’ error on MySQL Update query
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
SQL WITH clause example [duplicate]
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
ORA-00904: invalid identifier
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
What is the difference between varchar and nvarchar?
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
What is a stored procedure?
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
Case in Select Statement
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
Selecting COUNT(*) with DISTINCT
Count all the DISTINCT program names by program type and push number DISTINCT COUNT(*) will return a row for each unique count. What you want is COUNT(DISTINCT <expression>): evaluates expression for each row in a group and returns the number of unique, non-null values.
What is the difference between UNION and UNION ALL?
UNION removes duplicate records (where all columns in the results are the same), UNION ALL does not. There is a performance hit when using UNION instead of UNION ALL, since the database server must do additional work to remove the duplicate rows, but usually you do not want the duplicates (especially when developing reports). UNION Example: Result: UNION ALL example: Result: