MySQL Archives - Database Tips

SQL Count(*), Count(cte), Count(column), Count(pk), … x Inner and Outer Joins

In SQL, The Count function counts the number of values in a set. Such function accepts a parameter, that specifies[…]

To delete a great number of rows from a table may become a pain in the neck. A never ending[…]

It is really common to have columns that stores sequences of numbers in database systems (specially in relational databases). Users[…]

For many people, using noncorrelated subqueries (using In/Not In) seems to be more natural than using Exists/Not Exists and correlated[…]

Joins are one of the most common operators in SQL queries. In this post, we present inner and outer joins[…]

Duplicate data can be generated in the database due to design error, software bugs or misuse by end users. Depending[…]

Non-correlated subqueries (where the inner query does not have any column from the outer query tables) are usually implemented using[…]

LEAD and LAG are window functions that enable the simultaneous access to a table’s row and to other row related[…]

There are a lot of options to use when testing for NULL values in SQL. One should use built-in functions[…]

There is some confusion when dealing with some users and schemas. Some DBMS support several schemas per database, while other[…]