Selecting data from two different tables without using joins
You can do like this..
Database
Database sharding vs partitioning
Partitioning is more a generic term for dividing data across tables or databases. Sharding is one specific type of partitioning, part of what is called horizontal partitioning. Here you replicate the schema across (typically) multiple instances or servers, using some kind of logic or identifier to know which instance or server to look for the … Read more
mysql Foreign key constraint is incorrectly formed error
I ran into this same problem with HeidiSQL. The error you receive is very cryptic. My problem ended up being that the foreign key column and the referencing column were not of the same type or length. The foreign key column was SMALLINT(5) UNSIGNED and the referenced column was INT(10) UNSIGNED. Once I made them both the same … Read more
Can’t connect to local MySQL server through socket ‘/tmp/mysql.sock’ (2)
I have installed MySQL server and trying to connect to it, but getting the error: I have checked my /tmp directory and there is no mysql.sock. I can’t find mysql.sock anywhere. I read that it might be in But I checked there as well and there is even no mysql directory, only some postfix thing … Read more
SQL – HAVING vs. WHERE
WHERE clause introduces a condition on individual rows; HAVING clause introduces a condition on aggregations, i.e. results of selection where a single result, such as count, average, min, max, or sum, has been produced from multiple rows. Your query calls for a second kind of condition (i.e. a condition on an aggregation) hence HAVING works correctly. As a rule of thumb, use WHERE before GROUP BY and HAVING after GROUP BY. … Read more
Each GROUP BY expression must contain at least one column that is not an outer reference
To start with you can’t do this: The HAVING clause can only contain things which are attributes of the aggregate groups. In addition, 1, 2, 3 is not valid in GROUP BY in SQL Server – I think that’s only valid in ORDER BY. Can you explain why this isn’t what you are looking for:
What is the difference between Scope_Identity(), Identity(), @@Identity, and Ident_Current()?
The @@identity function returns the last identity created in the same session. The scope_identity() function returns the last identity created in the same session and the same scope. The ident_current(name) returns the last identity created for a specific table or view in any session. The identity() function is not used to get an identity, it’s used to create an identity in a select…into query. The … Read more
CREATE DATABASE permission denied in database ‘master’ (EF code-first)
Permission denied is a security so you need to add a “User” permission.. Right click you database(which is .mdf file) and then properties Go to security tab Click Continue button Click Add button Click Advance button Another window will show, then you click the “Find Now” button on the right side. On the fields below, … Read more
How to get size of mysql database?
Run this query and you’ll probably get what you’re looking for: This query comes from the mysql forums, where there are more comprehensive instructions available.
Warning: Null value is eliminated by an aggregate or other SET operation in Aqua Data Studio
You would mostly be using COUNT to summarize over a UID. Therefore COUNT([uid]) will produce the warning: Warning: Null value is eliminated by an aggregate or other SET operation. whilst being used with a left join, where the counted object does not exist. Using COUNT(*) in this case would also render incorrect results, as you would then be counting the … Read more