The difference is subtle, but it is a big difference. The ON condition stipulates which rows will be returned in the join, while the WHERE condition acts as a filter on the rows that actually were returned.Simple example: Consider a student table, consisting of one row per student, with student id and student name. In a second table, a list of grades that students have received, with student_id, subject, and grade. Give me a list of all students, and show their grade in Math. This requires a LEFT OUTER JOIN, because you want all students, and you know that some of them didn't take Math. Here a...

There are a lot of scalability challenges we see with clients over and over. The list could easily include 20, 50 or even 100 items, but we shortened it down to the biggest five issues we see.1. Tune those queriesBy far the biggest bang for your buck is query optimization. Queries can be functionally correct and meet business requirements without being stress tested for high traffic and high load. This is why we often see clients with growing pains, and scalability challenges as their site becomes more popular. This also makes sense. It wouldn't necessarily be a good use of time to tune a quer...

Many of you may have heard or used MySQL's query cache, because it used to be a popular way to improve MySQL's performance. As an important feature for improving MySQL's performance, the query cache was often recommended as a solution for slow queries. However, why has MySQL 8 abandoned the query cache? Today, we will analyze and explore this decision.What is query cache?According to official document:The query cache stores the text of a SELECT statement together with the corresponding result that was sent to the client. If an identical statement is received later, the server retriev...

To create trigger in MySQL, the syntax is :CREATE [DEFINER = { user | CURRENT_USER }] TRIGGER trigger_name trigger_time trigger_event ON tbl_name FOR EACH ROW trigger_bodyOne example is :DELIMITER %%DROP TRIGGER IF EXISTS delete_commentCREATE TRIGGER delete_comment AFTER DELETE ON file_generate_infoFOR EACH ROW BEGIN DELETE FROM article_comment WHERE article_id=OLD.article_id;END%%The whole create trigger statement should be complete statement but not many separate commands. So we use %% as the statement delimiter. You can choose other symbols as delimiter as well....

Blocking is a common occurrence in an SQL server context, but if you are new to the world of database management you might not know what this issue entails and perhaps even fear that it is a sign of serious underlying problems.To allay your fears and clear up the mystery, here is a brief overview of blocking and the steps you can take to tackle it.Image Source: PixabaySQL blocking explainedSQL blocking according to SentryOne is an offshoot of the way that concurrent databases operate. Because processes can be executed simultaneously, it is likely that at some point more than one process will n...