Skip to main content

Foreign Key References (Tickler)

 

Find All Foreign Key References

In my experience, a well-Normalized database winds up with lots of Foreign Key relationships between the tables. They are a real benefit, bringing so much ease and power in preserving data integrity. Best of all, they pass responsibility for maintaining that integrity to the RDBMS itself, rather than burying it in application code.

Looking at one table, it is relatively easy to see its list of Foreign Keys outward, to other tables.

Occasionally, though, we need to know what other tables have a Foreign Key defined for a given table. It is rare enough that I usually forget some of the little details in between uses. Rather than needing to do a web search every time, this Tickler post will help to jog my memory.

MySQL

-- what FKs reference this data?

SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE REFERENCED_TABLE_SCHEMA = 'MySchema'
AND REFERENCED_TABLE_NAME = 'MyTable';


These "memory tickler" posts are quick-hits to refresh my mind about little technical details that arise infrequently enough that I forget in between, and wind up doing an internet search every time. By posting them here, they will be easier to find as needed.)

Labels:

Popular posts from this blog

How to do Git Rebase in Eclipse

This is an abbreviated version of a fuller post about Git Rebase in Eclipse. See the longer one here : One side-effect of merging Git branches is that it leaves a Merge commit. This can create a history view something like: The clutter of parallel lines shows the life spans of those local branches, and extra commits (nine in the above screen-shot, marked by the green arrows icon). Check out this extreme-case history:  http://agentdero.cachefly.net/unethicalblogger.com/images/branch_madness.jpeg Merge Commits show all the gory details of how the code base evolved. For some teams, that’s what they want or need, all the time. Others may find it unnecessarily long and cluttered. They prefer the history to tell the bigger story, and not dwell on tiny details like every trivial Merge-commit. Git Rebase offers us 2 benefits over Git Merge: First, Rebase allows us to clean up a set of local commits before pushing them to the shared, central repository. For this
Read more

Java 8: Rewrite For-loops using Stream API

Java 8 Tip: Anytime you write a Java For-loop, ask yourself if you can rewrite it with the Streams API. Now that I have moved to Java 8 in my work and home development, whenever I want to use a For-loop, I write it and then see if I can rewrite it using the Stream API. For example: I have an object called myThing, some Collection-like data structure which contains an arbitrary number of Fields. Something has happened, and I want to set all of the fields to some common state, in my case "Hidden"
Read more

Git Reset in Eclipse

Using Git and the Eclipse IDE, you have a series of commits in your branch history, but need to back up to an earlier version. The Git Reset feature is a powerful tool with just a whiff of danger, and is accessible with just a couple clicks in Eclipse. In Eclipse, switch to the History view. In my example it shows a series of 3 changes, 3 separate committed versions of the Person file. After commit 6d5ef3e, the HEAD (shown), Index, and Working Directory all have the same version, Person 3.0.
Read more

Code Coverage in C#.NET Unit Tests - Setting up OpenCover

The purpose of this post is to be a brain-dump for how we set up and used OpenCover and ReportGenerator command-line tools for code coverage analysis and reporting in our projects. The documentation made some assumptions that took some digging to fully understand, so to save my (and maybe others') time and effort in the future, here are my notes. Our project, which I will call CEP for short, includes a handful of sub-projects within the same solution. They are a mix of Web APIs, ASP MVC applications and Class libraries. For Unit Tests, we chose to write them using the MSTest framework, along with the Moq mocking framework. As the various sub-projects evolved, we needed to know more about the coverage of our automated tests. What classes, methods and instructions had tests exercising them, and what ones did not? Code Coverage tools are conveniently built-in for Visual Studio 2017 Enterprise Edition, but not for our Professional Edition installations. Much less for any Commun
Read more

Scala Collections: A Group of groupBy() Examples

Scala provides a rich Collections API. Let's look at the useful groupBy() function. What does groupBy() do? It takes a collection, assesses each item in that collection against a discriminator function, and returns a Map data structure. Each key in the returned map is a distinct result of the discriminator function, and the key's corresponding value is another collection which contains all elements of the original one that evaluate the same way against the discriminator function. So, for example, here is a collection of Strings: val sports = Seq ("baseball", "ice hockey", "football", "basketball", "110m hurdles", "field hockey") Running it through the Scala interpreter produces this output showing our value's definition: sports: Seq[String] = List(baseball, ice hockey, football, basketball, 110m hurdles, field hockey) We can group those sports names by, say, their first letter. To do so, we need a disc
Read more