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.
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 … Read more
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 … Read more
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 … Read more
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 … Read more
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.
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. … Read more