Hi, If my englsih is so bad, i'll try to explain and stop this thread now. I'm not teaching, i'm answering questions. If someone wants to read docs, he (she) doesn't ask a question on the list. So if i answer, i answer the question, just the question.
You want to know my level of knowledgne, 10 years, oracle, sybase, sqlserver, db2. I can help for migration from or to... I said don't use joins for the query given in the example or queries using just the joining columns from the first table. Normal forms is bla bla here ... See also about covering indexes. That can help. This is the query given by Jeff : >>> So, if record 100 in table1 links to 5 corresponding records in table2, >>> I want to pull the latest record from table2 where table2.parentid = 100 and table2.user not like 'john' The only clause is about table2.parentid = 100 or child.id = 100. that's the same. All the other clauses are on table2. This is the exampel given by Jeff. If you want absolutely LEFT outer joins for that (without other columns from table1), i say you good luck, this can (also) do the trick. That's all. ----------------- If you give me real examples, i can help you to give you to find the right (if i can) query plan. Tuning is my first target when i think a query. I never suggest nested loops, but relationnal algebra. I'm not supposed speeking to students but DBAs, for specific question. Sorry if i run up against your sensitivity, but we are not speaking about the same thing. And please if you have to criticize or complete an answer, it's your right. The list is for that. If you want to speak to me as your student, this is enough. I never did it when i was teacher 11 years ago. Best Regards -------------------- Mathias FATENE Hope that helps *This not an official mysql support answer -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: lundi 25 avril 2005 23:02 To: mathias fatene Cc: 'Jeff McKeon'; mysql@lists.mysql.com; [EMAIL PROTECTED] Subject: RE: Query question "mathias fatene" <[EMAIL PROTECTED]> wrote on 04/25/2005 04:24:42 PM: > Hi, > Im sorry to disappoint you but this is an anti-performance solution. > Use joins rathers than subqueries, and don't use joins if you can (all > data in the mother table). > > Imagine that table2 has 30.000.000 records, and not good indexes. you > can wait for your answer a long time. > > Best Regards > -------------------- > Mathias FATENE > > Hope that helps > *This not an official mysql support answer > <snip> Mathias, I do appreciate your energy and willingness to contribute to the list. I am not affiliated with MySQL or any of its subsidiaries and I have no special privileges to police what happens on this list. I am a fellow contributor just as you. With that said, I feel that I must seriously question your level of experience and ability to form useful responses. When you say "and don't use joins if you can (all data in the mother table)", It seems to me that you are proposing that in order to eliminate JOINs in queries that all data should be flattened into one single table. Not only is this incorrect advice but it undermines the many reasons for using a relational database system (RDBMS) in the first place. I would love to compare the performance of a properly normalized and indexed relational data structure against a single "flat" table for all but the most trivial of data sets. The nomalized data will not only take up less room on the disk but it will perform extremely well (especially for larger data sets). The single-table model you proposed will not scale to more than a few hundred thousand rows before the table's size becomes a bottleneck. Some queries will take "a long time" to finish against 30 million row tables, even with good indexes on them. Your extreme counter example was a non-starter. The original poster acknowledges that they are new (no offence intended) and I feel that your posts were hardly helpful at best and most likely counter-productive. Please, take the time to read your ansers from the perspective of the person you are responding to. Try to keep in mind not only their language skills (as this is a multi-national list) but their experience level and even sometimes their age (we have many students looking for help on here and some of them are still teenagers). Please be more accurate, thoughtful, and descriptive the next time you post, OK? With greatest humility, Shawn Green Database Administrator Unimin Corporation - Spruce Pine -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
