MySQL Diary

Even if you think you know everything about LEFT JOIN, I bet you will learn something or two in this post! A reminder about “A LEFT JOIN B ON conditional_expr” The ON condition (in the expression “A LEFT JOIN B ON conditional_expr”) is used to decide how to retrieve rows from table B (Matching-Stage). If [...]

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 [...]