1. Not using appropriate indices This is a relatively easy one but still it happens all the time. Foreign keys should have indexes on them. If you’re using a field in a WHERE you should (probably) have an index on it. Such indexes should often cover multiple columns based on the queries you need to … Read more
We need to know all the FDs (functional dependencies) that hold to determine CKs (candidate keys), not just those in some list. Look at a (correct & general) definition of CK or algorithm for finding CKs (in a published textbook, not a youtube video). Is your list appropriately a closure (all the FDs that hold) … Read more
Short answer: yes. Long answer: You need your table to be joinable on something If you want your table to be clustered, you need some kind of a primary key. If your table design does not need a primary key, rethink your design: most probably, you are missing something. Why keep identical records? In MySQL, … Read more
The basic idea is that you have two numbers to make up a primary key- a “high” number and a “low” number. A client can basically increment the “high” sequence, knowing that it can then safely generate keys from the entire range of the previous “high” value with the variety of “low” values. For instance, … Read more
Here is a link to the official docs which include the main points in this answer: android.database.sqlite package-level javadoc Kotlin code to get framework SQLite version (tip: just stick a breakpoint in your Activity onCreate() and use this code in Evaluate Expression…): val version = android.database.sqlite.SQLiteDatabase.create(null).use { android.database.DatabaseUtils.stringForQuery(it, “SELECT sqlite_version()”, null) } “Framework (API ${android.os.Build.VERSION.SDK_INT}) … Read more
A relation has an associated set of columns of any type and an associated set of rows. There is one value per column per row. Sometimes “normalize” is used to mean (1) “decompose each relation to smaller relations that are its projections and that join back to it”. This is normalization to higher NFs (normal … Read more
The <p:graphicImage> requires a special getter method. It will namely be invoked twice per generated image, each in a completely different HTTP request. The first HTTP request, which has requested the HTML result of a JSF page, will invoke the getter for the first time in order to generate the HTML <img> element with the … Read more
Based on your question history, you’re using JSF 2.x. So, here’s a JSF 2.x targeted answer. In JSF 1.x you would be forced to wrap item values/labels in ugly SelectItem instances. This is fortunately not needed anymore in JSF 2.x. Basic example To answer your question directly, just use <f:selectItems> whose value points to a … Read more
You are correct that storing the password in a plain-text field is a horrible idea. However, as far as location goes, for most of the cases you’re going to encounter (and I honestly can’t think of any counter-examples) storing the representation of a password in the database is the proper thing to do. By representation … Read more