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:
SQL Server databases use two files – an MDF file, known as the primary database file, which contains the schema and data, and a LDF file, which contains the logs. See wikipedia. A database may also use secondary database file, which normally uses a .ndf extension. As John S. indicates, these file extensions are purely convention …
Assuming you’re joining on columns with no duplicates, which is a very common case: An inner join of A and B gives the result of A intersect B, i.e. the inner part of a Venn diagram intersection. An outer join of A and B gives the results of A union B, i.e. the outer parts of a …
Assuming you’re joining on columns with no duplicates, which is a very common case: An inner join of A and B gives the result of A intersect B, i.e. the inner part of a Venn diagram intersection. An outer join of A and B gives the results of A union B, i.e. the outer parts of a …
Open & Edit /etc/my.cnf or /etc/mysql/my.cnf, depending on your distro. Add skip-grant-tables under [mysqld] Restart Mysql You should be able to login to mysql now using the below command mysql -u root -p Run mysql> flush privileges; Set new password by ALTER USER ‘root’@’localhost’ IDENTIFIED BY ‘NewPassword’; Go back to /etc/my.cnf and remove/comment skip-grant-tables Restart Mysql Now you will be able to login with the new …
4 I take an index on the barcode column as a given. You could save space if you stored the codes as numbers. Space is time as less bytes can be read faster. Also, the lookup should be faster on numbers. The leading zeros can be reconstructed when needed as UPC-A is a fixed-length code.
Open & Edit /etc/my.cnf or /etc/mysql/my.cnf, depending on your distro. Add skip-grant-tables under [mysqld] Restart Mysql You should be able to login to mysql now using the below command mysql -u root -p Run mysql> flush privileges; Set new password by ALTER USER ‘root’@’localhost’ IDENTIFIED BY ‘NewPassword’; Go back to /etc/my.cnf and remove/comment skip-grant-tables Restart Mysql Now you will be able to login with the new …
The second (assuming you means CONTAINS, and actually put it in a valid query) should be faster, because it can use some form of index (in this case, a full text index). Of course, this form of query is only available if the column is in a full text index. If it isn’t, then only the first form is available. …
192 MySQL is an example of a relational database – you would use an ORM to translate between your objects in code and the relational representation of the data. Examples of ORMs are nHibernate, Entity Framework, Dapper and more… MongoDB is an example of a document database – you would use an ODM to translate …
Introduction Object-Relational Mapping (ORM) is a technique that lets you query and manipulate data from a database using an object-oriented paradigm. When talking about ORM, most people are referring to a library that implements the Object-Relational Mapping technique, hence the phrase “an ORM”. An ORM library is a completely ordinary library written in your language …