A SELECT statement with COUNT returns the number of rows retrieved by the SELECT statement. For performance, the desired result is to limit that count. Including a LIMIT clause in the SELECT statement will not work since it only restricts the number of rows returned, which is always one. The solution, what I call “Limited-Count”, [...]
One way to do a “Conditional Join” in MySQL is by using a “LEFT JOIN”. Create a “LEFT JOIN” for each condition and combine the results into one column using an “IF” statement by the “SELECT” expression. Here’s an example: Suppose you have three tables: questions: a table consisting of question ids, timestamps, and whether [...]
Question: How can you select records from one table that doesn’t have a specific ID in a second, many-to-many table? In other words, imagine you have a questions table (A), categories table (B), and a many-to-many relationship link table (L). This setup allows a question to have several categories. How can you find questions that [...]
A while ago, I were searching for a way to produce random rows from a table in MySQL. I found several solutions but none of them satisfied me. Of course, I could use a combined logic of MySQL and a programming language. For example by producing random numbers in PHP and using them in the MySQL query in a IN clouse. However, I [...]