a generic question about database table
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Southmountain wrote:
now I have a big table in a database, what is the best way to get understanding of this table quickly?
Documentation. If there's a table, there's a developer and there should be documentation.
Southmountain wrote:
it has hundreds of fields and I only know some keys.
Hundreds of fields?? DROP TABLE would be the best start; no normalized table contains that much fields. I'm serious; no such table should exist. You asking how to understand it implies no documentation either. Name your company.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
yes, it has limited documentation ....
diligent hands rule....
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I found MS Access and Excel, with some SQL management studio, good enough for "data analysis". Access and Excel can connect to SQL server. You can then tap into their analytics and query ability. There's also MS Power BI (Desktop), to top it off.
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
following your ideas, I will try to load it into an Excel pivot table and play around with it...
diligent hands rule....
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Southmountain wrote:
now I have a big table in a database, what is the best way to get understanding of this table quickly?
Documentation. If there's a table, there's a developer and there should be documentation.
Southmountain wrote:
it has hundreds of fields and I only know some keys.
Hundreds of fields?? DROP TABLE would be the best start; no normalized table contains that much fields. I'm serious; no such table should exist. You asking how to understand it implies no documentation either. Name your company.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
I will double check the table column number and have very limited documents...
diligent hands rule....
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In the early 1980s, one model that was proposed was 'the universal relation'. The data base had a single relation (table), for all applications. A new application might need some new fields/columns, and added those, but usually it also made use of columns already in the universal relation. There was at least one implementation of this model - I'm sorry, I can't remember what it was called - and the developers claimed that having everything in one relation drastically simplified some query optimizations. I see that the idea even has a brief Wikipedia entry: Universal relation assumption[^] stating that "real database designs is often plagued with a number of difficulties". So there were reasons why it didn't succeed. Yet, it did have some pros and benefits as well. Maybe those designing this relation you have been introduced to were trying to collect some of those. The Wikipedia article links to a slide set for a talk, "Who won the Universal Relation war?". It is very much a slide set - you can't learn much about Universal Relations from it. But it gives you a certain impression of the magnitude and intensity of the debate, 30-40 years ago.
Although it used SQL as the backend, I remember a Customer Relationship Management system called Maximiser that took a similar approach. There were, ISTR just two tables, one to hold all the relatively constant client data itself and one to hold the collection of notes linked to that. In the Maximiser app there were complex joins on one table producing 'subtables' that held various views on the data. Some columns contained numbers that indicated what other columns actually held! I was given the job of moving all the data held in this system to another SQL based program. It took ages (in the absence of any database schema documentation) to unravel the various actual combinations of joins required to get what we wanted. Here's just one query to extract a little of the info: All the tables named as a, b, c, d etc duplicate joins used in 'built-in' queries on the maximiser database. I thought you might find an example of the stuff I had to build mildly amusing 8)
-- Build the View of the Maximiser data that shows what we want and store it
SELECT
CASE
WHEN c.Record_Type = 1 THEN c.Name
WHEN c.Record_Type = 31 THEN d.Name + ' - ' + c.First_Name + ' ' + c.Name
WHEN c.Record_Type = 2 AND len(c.Firm) > 0 THEN c.Firm
WHEN c.Record_Type = 2 AND len(c.Firm) < 1 THEN c.First_Name + ' ' + c.Name
WHEN c.Record_Type = 32 THEN
(
CASE
WHEN len(d.Firm) > 0 THEN d.Firm + ' - ' + c.First_Name + ' ' + c.Name
WHEN len(d.Firm) < 1 THEN d.First_Name + ' ' + d.Name + ' - ' + c.First_Name + ' ' + c.Name
END
)
ELSE c.Name
END AS Company,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.Address_Line_1
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.Address_Line_1
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.Address_Line_1
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.Address_Line_1
ELSE c.Address_Line_1
END AS Address_1,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.Address_Line_2
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.Address_Line_2
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.Address_Line_2
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.Address_Line_2
ELSE c.Address_Line_2
END AS Address_2,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.City
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.City
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.City
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.City
ELSE c.City
END AS C -
now I have a big table in a database, what is the best way to get understanding of this table quickly? it has hundreds of fields and I only know some keys. I have some basic ideas already, but I would like to learn some new tricks from gurus here. Somehow I am a little addicted to ask questions here.
diligent hands rule....
see if you can get an input screen (or a few) and some reports and open/run it for a specific record. Next you need to try and see if you can match the data for a specific record to fields on the input screens or reports. That will give you a good understanding of how some of the fields fit together.
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If you design a database, you normalize the model.
jschell wrote:
I think there was something like 300 or 400 columns
Give or take 50 columns. That's not design, that's a disaster.
jschell wrote:
Probably could not have dropped it. It held credit card transaction data.
That's why I stopped visiting the hospital. I don't wont to die by VB6.
Bastard Programmer from Hell :suss: "If you just follow the bacon Eddy, wherever it leads you, then you won't have to think about politics." -- Some Bell.
-
In the early 1980s, one model that was proposed was 'the universal relation'. The data base had a single relation (table), for all applications. A new application might need some new fields/columns, and added those, but usually it also made use of columns already in the universal relation. There was at least one implementation of this model - I'm sorry, I can't remember what it was called - and the developers claimed that having everything in one relation drastically simplified some query optimizations. I see that the idea even has a brief Wikipedia entry: Universal relation assumption[^] stating that "real database designs is often plagued with a number of difficulties". So there were reasons why it didn't succeed. Yet, it did have some pros and benefits as well. Maybe those designing this relation you have been introduced to were trying to collect some of those. The Wikipedia article links to a slide set for a talk, "Who won the Universal Relation war?". It is very much a slide set - you can't learn much about Universal Relations from it. But it gives you a certain impression of the magnitude and intensity of the debate, 30-40 years ago.
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now I have a big table in a database, what is the best way to get understanding of this table quickly? it has hundreds of fields and I only know some keys. I have some basic ideas already, but I would like to learn some new tricks from gurus here. Somehow I am a little addicted to ask questions here.
diligent hands rule....
Southmountain wrote:
what is the best way to get understanding of this table quickly?
There isn't one. There are tools and scripts for most DBs that can create some type of analysis for you, but you really don't need to understand the fields, you need to understand the data. We can all grouse and speculate about the "100s of fields", but let's assume there is a valid reason for them even though I'm hard pressed to come up with one. What type of understanding are you trying to achieve? Data is data and the question is if and where it is used. I'd suspect there could be a lot of drop columns in your future, but that requires a detailed look at your recordset objects in the code that is using the DB. Honestly, it's a flat table so despite the crazy column count, it should be clear to understand. If it has a bunch of relations, that could take a lot of caffeine or alcohol, or both :) What's your scope of work in relation to this monster? Crazy as it seems, the DB could be oddly efficient depending on the use of the data. You know, Select * (perish the thought!) from tablename where id=x is pretty simple, lol. If your task is to clean up and reduce the size of the database, that is one thing. If you're stuck with it, it is what it is and how the data is used is of the utmost importance.
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now I have a big table in a database, what is the best way to get understanding of this table quickly? it has hundreds of fields and I only know some keys. I have some basic ideas already, but I would like to learn some new tricks from gurus here. Somehow I am a little addicted to ask questions here.
diligent hands rule....
Understand ‘quickly?’: probably not possible. Step back. Look at the application and the interfaces that update the table. Depending on the database tech, there’ll be a way to search procedures for the table name. Study these procedures. Then (or while doing the above) look at a subset of the data, such as the last day’s worth of records. Good luck. ;)
Time is the differentiation of eternity devised by man to measure the passage of human events. - Manly P. Hall Mark Just another cog in the wheel
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Although it used SQL as the backend, I remember a Customer Relationship Management system called Maximiser that took a similar approach. There were, ISTR just two tables, one to hold all the relatively constant client data itself and one to hold the collection of notes linked to that. In the Maximiser app there were complex joins on one table producing 'subtables' that held various views on the data. Some columns contained numbers that indicated what other columns actually held! I was given the job of moving all the data held in this system to another SQL based program. It took ages (in the absence of any database schema documentation) to unravel the various actual combinations of joins required to get what we wanted. Here's just one query to extract a little of the info: All the tables named as a, b, c, d etc duplicate joins used in 'built-in' queries on the maximiser database. I thought you might find an example of the stuff I had to build mildly amusing 8)
-- Build the View of the Maximiser data that shows what we want and store it
SELECT
CASE
WHEN c.Record_Type = 1 THEN c.Name
WHEN c.Record_Type = 31 THEN d.Name + ' - ' + c.First_Name + ' ' + c.Name
WHEN c.Record_Type = 2 AND len(c.Firm) > 0 THEN c.Firm
WHEN c.Record_Type = 2 AND len(c.Firm) < 1 THEN c.First_Name + ' ' + c.Name
WHEN c.Record_Type = 32 THEN
(
CASE
WHEN len(d.Firm) > 0 THEN d.Firm + ' - ' + c.First_Name + ' ' + c.Name
WHEN len(d.Firm) < 1 THEN d.First_Name + ' ' + d.Name + ' - ' + c.First_Name + ' ' + c.Name
END
)
ELSE c.Name
END AS Company,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.Address_Line_1
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.Address_Line_1
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.Address_Line_1
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.Address_Line_1
ELSE c.Address_Line_1
END AS Address_1,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.Address_Line_2
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.Address_Line_2
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.Address_Line_2
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.Address_Line_2
ELSE c.Address_Line_2
END AS Address_2,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.City
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.City
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.City
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.City
ELSE c.City
END AS COoof, that would be nasty to maintain!
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now I have a big table in a database, what is the best way to get understanding of this table quickly? it has hundreds of fields and I only know some keys. I have some basic ideas already, but I would like to learn some new tricks from gurus here. Somehow I am a little addicted to ask questions here.
diligent hands rule....
This mostly applies if it's a relational table. There a lot of excellent responses here, but one topic that I didn't see explicitely mentioned was "Normalization". Normalize the data. You might need to have a sample of data to work(play) with to understand. There are better resources to explain normalization further, and *some* SQL books hit the topic early (the good ones, anyway). Normalization is at the root of what many here have indicated are problems - like too many columns in individual tables! You likely have key fields and data fields repeating all through your data. Even if you can't change the tables, understanding how it isn't normalized will help you understand the data better. (Maybe a future task will let you fix this) > You'll need to understand the domain. It would be great if you have some people that can get you pointed in the best area. It sounds like there is a lot more complexity than can be dealt with quickly. > Maybe there's a program that uses that table that might reveal columns content or purpose? > Review a small sample of data in a dev/work database. > For longer-term goals >try to use the right terms too, especially when consulting your database expert. e.g. It might be habit to say 'fields', but in the relational database world it's a 'column'. Stuff like that will make communication more consistent. > Maintain a group of documents, references for yourself of what you're finding - and share it. > Topics and terms to be familiar with, or review: > the different between a data table versus a reference table > A Many-to-Many relationship and a "Join Table" (sometimes called a "Pin Table" etc. ...but not by me) I didn't intend to write a book here! You have too much to read here already! I wish you success!
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Although it used SQL as the backend, I remember a Customer Relationship Management system called Maximiser that took a similar approach. There were, ISTR just two tables, one to hold all the relatively constant client data itself and one to hold the collection of notes linked to that. In the Maximiser app there were complex joins on one table producing 'subtables' that held various views on the data. Some columns contained numbers that indicated what other columns actually held! I was given the job of moving all the data held in this system to another SQL based program. It took ages (in the absence of any database schema documentation) to unravel the various actual combinations of joins required to get what we wanted. Here's just one query to extract a little of the info: All the tables named as a, b, c, d etc duplicate joins used in 'built-in' queries on the maximiser database. I thought you might find an example of the stuff I had to build mildly amusing 8)
-- Build the View of the Maximiser data that shows what we want and store it
SELECT
CASE
WHEN c.Record_Type = 1 THEN c.Name
WHEN c.Record_Type = 31 THEN d.Name + ' - ' + c.First_Name + ' ' + c.Name
WHEN c.Record_Type = 2 AND len(c.Firm) > 0 THEN c.Firm
WHEN c.Record_Type = 2 AND len(c.Firm) < 1 THEN c.First_Name + ' ' + c.Name
WHEN c.Record_Type = 32 THEN
(
CASE
WHEN len(d.Firm) > 0 THEN d.Firm + ' - ' + c.First_Name + ' ' + c.Name
WHEN len(d.Firm) < 1 THEN d.First_Name + ' ' + d.Name + ' - ' + c.First_Name + ' ' + c.Name
END
)
ELSE c.Name
END AS Company,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.Address_Line_1
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.Address_Line_1
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.Address_Line_1
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.Address_Line_1
ELSE c.Address_Line_1
END AS Address_1,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.Address_Line_2
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.Address_Line_2
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.Address_Line_2
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.Address_Line_2
ELSE c.Address_Line_2
END AS Address_2,
CASE
WHEN c.Address_Id > 0 AND c.Record_Type IN (1, 31) THEN e.City
WHEN c.Address_Id < 1 AND c.Record_Type = 31 THEN g.City
WHEN c.Address_Id > 0 AND c.Record_Type IN (2, 32) THEN f.City
WHEN c.Address_Id < 1 AND c.Record_Type = 32 THEN g.City
ELSE c.City
END AS CI just saw something similar the other day with additional complications. The developer that inherited was trying to figure out how to make it a little more maintainable by removing some conditions that were nonsensical and others that were just bad hard codes.
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now I have a big table in a database, what is the best way to get understanding of this table quickly? it has hundreds of fields and I only know some keys. I have some basic ideas already, but I would like to learn some new tricks from gurus here. Somehow I am a little addicted to ask questions here.
diligent hands rule....
-
now I have a big table in a database, what is the best way to get understanding of this table quickly? it has hundreds of fields and I only know some keys. I have some basic ideas already, but I would like to learn some new tricks from gurus here. Somehow I am a little addicted to ask questions here.
diligent hands rule....
I work for a finance institution, and our tables are highly un-normalized with all the problems this incurs. we have many tables with hundreds of columns. But people in finance are used to excel like spreadsheet and they want to see everything at one place. I came to that place with a background in databases and I was horrified and still am. But it is hard to change legacy code AND mentalities. So for better or worse I'm stuck with it. The best advice I can give you: find the queries people/programs make the most often, this often reveal the «subtables» within the big one. Also if you have self join that often indicate two tables (or more) sharing the same table data. Once you have that draw a diagram as if those tables really exist. If you can create views that represent those tables. This way you will better understand the «schema»
Quote:
«Il faut imaginer Sisyphe heureux» Albert Camus