| Subject | Re: complex indexes vs index key fields |
| From | Akshat Kapoor <akshat.kapoor@kapoorsons.in> |
| Date | Fri, 31 Jul 2020 20:06:49 +0530 |
| Newsgroups | dbase.getting-started |
> The MySQL documentation covers everything you need but it doesn't get > you started in SQL. There are, however, plenty of SQL tutorials on the > Internet. I found https://www.w3schools.com/sql/default.asp useful as > it highlights the fact, and gives examples, that different SQL servers > use different syntax for some operations. > > The tutorials do, unfortunately, only cover the basics. The syntax is a > bit different to doing the same things in dBASE but it shouldn't give > you any problems. Once you get a bit deeper into SQL you should be able > to get any help you need in the sql-server newsgroup. Very True. > All tables MUST have a primary key otherwise you won't be able to UPDATE > or DELETE specific records. This is often an autoinc type field but it > can, in fact, consist of multiple fields. For instance, the primary key > for your energydata could be a combination of siteId and eTimestamp. I prefer autoinc as they do not require any maintenance. SiteID and eTimestamp can serve as a combination but what will be there to prevent accidental duplicates. But I never encountered this kind of situation before hence cannot say. > Something to bear in mind is that there are no soft deletes in SQL. In > ..dbf files records are not physically removed from the table when they > are deleted. They can actually be brought back using the RECALL command > as long as this is done before the table is PACKed. In SQL gone is > gone. It helps to have regular backups "just in case". I don't use > MySQL but Akshat will be able to help you with this. Gone is GONE. For backups I would recommend viewing the last few posts of the thread "How can I restore MySQL database from a recovered hard disk" by Emeka on 13th July 2020 That program is not for MySQL alone. With just change in a few lines of the commands it can be used for firebird also, or for any other RDBMS which offers command line utilities for backups. Regards Akshat | |