After selecting data from multiple tables, like this:
SELECT games.name, scores.score
FROM games, scores
WHERE players.id = scores.player_id
..can I extract the column headings of this newly generated table?
The statement I'd normally use would be as follows:
SELECT column_name
FROM information_schema.columns
WHERE table_name=table
But naturally this would not work for a dynamically generated table with no name
Help much appreciated!
Edit: I'm using the MariaDB client
..can I extract the column headings of this newly generated table?
No. Mostly because you've not created a table. Just a result set. I think you already know this, because you've already looked at the information schema :)
Unfortunately it seems even creating a temporary table won't help - because those aren't stored in the information schema either. I don't think you can declare cursors for SHOW COLUMN... statements either.
I don't think you've got a way to do it I'm afraid.
If it's a prepared statement (with the select statement held in a variable) you could probably chop it up using some ugly string manipulation...?
It might at this point be worth asking "more abstractly, what problem are you trying to solve?"
Related
I have two tables in MySQL with 100+ columns. I need to figure out the columns in both tables which have some of the same values. I need a way to find out which columns are matching in terms of type and values in them so that I can use them in joins and extract results from them. I can convert the tables in excel sheet and apply VB Script as well. Any kind of help is greatly appreciated.
There's no magical SQL query you can run to determine the logic behind how your database was designed. You can check the table schema to see if there are any foreign keys enabled, but that's about it.
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'my_database_name' AND TABLE_NAME ='my_table';
Based on how you describe the tables, the given design sounds... odd. I hope whoever designed it left you documentation. Your last resort is going to be just dumping the data and looking for patterns.
I'm building a MySQL event to make a copy of a table in the database with a timestamp in the name.
CREATE TABLE `db_name`.`tbl_prefix_(SELECT TO_SECONDS(NOW()))` ( [the rest...]
Obviously this isn't working. What should I do to make it work?
Any suggestions are welcome.
Thanks
This is a bad architecture. Generating tables on the fly is not something you should do.
Instead, create a single table with a timestamp column. For instance, if you would before have 3 tables with three timestamps A, B, and C, you now have one table with a timestamp column containing the values A, B, and C, respectively.
In order to do this, you would need to use "dynamic SQL". That is, make use of the MySQL PREPARE statement.
What you'd need to do is populate a variable with a string that contains the SQL text you want to execute. Doing variable substitution into string is trivial.
The "trick" is to take that dynamic string and execute it like it was a SQL statement.
And that's what the PREPARE statement does for us, takes in a variable, and reads the contents of that variable like it were a SQL statement.
With that said, rather than give an example code that demonstrates this in more detail, I'm going to suggest that you re-think this idea of creating a table with timestamp value as part of the name.
What problem is that designed to solve? And carefully consider whether the proposed design for a solution will introduce a bigger problem than it solves.
I'd like to select * from 2 tables, but have each table's column name be prefixed with a string, to avoid duplicate column name collissions.
For example, I'd like to have a view like so:
CREATE VIEW view_user_info as (
SELECT
u.*,
ux.*
FROM
user u,
user_ex ux
);
where the results all had each column prefixed with the name of the table:
e.g.
user_ID
user_EMAIL
user_ex_ID
user_ex_TITLE
user_ex_SIN
etc.
I've put a sql fiddle here that has the concept, but not the correct syntax of course (if it's even possible).
I'm using MySql, but would welcome generic solutions if they exist!
EDIT: I am aware that I could alias each of the fields, as mentioned in one of the comments. That's what I'm currently doing, but I find at the start of a project I keep having to sync up my tables and views as they change. I like the views to have everything in them from each table, and then I manually select out what I need. Kind of a lazy approach, but this would allow me to iterate quicker, and only optimize when it's needed.
I find at the start of a project I keep having to sync up my tables and views as they change.
Since the thing you're trying to do is not really supported by standard SQL, and you keep modifying database structures in development, I wonder if your best approach would be to write a little script that recreates that SELECT statement for you. Maybe wrap it in a method call in the development language of your choice?
Essentially you'd need to query INFORMATION_SCHEMA for the tables and columns of interest, probably via a join, and write the results out in SQL style.
Then just run the script every time you make database structural changes that are important to you, and watch your code magically keep up.
I know that this might seem like a strange question, but let me try and explain it. I have a database table called 'plan' and in it the first column is called 'username' and the columns after it are called 'question1', 'question2' and so on. I now need to add a hundred or so more columns named like this, but it would be nice to have a sql statement that would automatically do that for me.
I know this wasn't set up in the best way, but if you have a solution, please let me know :)
There isn't any SQL command or feature that would do this automatically; sure you can generate the alter table statements and add the columns programmatically; however, your design would be terribly flawed.
Instead of adding columns, you should create a table containing the question, the user_id (or username, whatever is the PK) to hold the records. If you need to identify a question by number (or ID), simply add another column called question_id.
Write the query in sql to excel. Seperate the incrementing number. Drag down until excel row 100. Hard to explain but i guess you ll figure it out. You'll have 100 incrementing add column sql statements. copy paste run it on a query tool.
Is there a way that I can do a select as such
select * from attributes where product_id = 500
would return
id name description
1 wheel round and black
2 horn makes loud noise
3 window solid object you can see through
and the query
select * from attributes where product_id = 234
would return the same results as would any query to this table.
Now obviously I could just remove the where clause and go about my day. But this involves editing code that I don't really want to modify so i'm trying to fix this at the database level.
So is there a "magical" way to ignore what is in the where clause and return whatever I want using a view or something ?
Even if it was possible, I doubt it would work. Both of those WHERE clauses expect one thing to be returned, therefore the code would probably just use the first row returned, not all of them.
It would also give the database a behaviour that would make future developers pull their hair out trying to understand.
Do it properly and fix the code.
or you could pass "product_id" instead of an integer, if there's no code checking for that...so the query would become:
select * from attributes where product_id = product_id;
this would give you every row in the table.
If you can't edit the query, maybe you can append to it? You could stick
OR 1=1
on the end.
You may be able to use result set metadata to get what you want, but a result set won't have descriptions of fields. The specific API to get result set metadata from a prepared query varies by programming language, and you haven't said what language you're using.
You can query the INFORMATION_SCHEMA for the products table.
SELECT ordinal_position, column_name, column_comment
FROM INFORMATION_SCHEMA.columns
WHERE table_name = 'products' AND schema_name = 'mydatabase';
You can restructure the database into an Entity-Attribute-Value design, but that's a much more ambitious change than fixing your code.
Or you can abandon SQL databases altogether, and use a semantic data store like RDF, which allows you to query metadata of an entity in the same way you query data.
As far out as this idea seems I'm always interested in crazy ways to do things.
I think the best solution I could come up with is to use a view that uses the products table to get all the products then the attributes table to get the attributes, so every possible product is accounted for and all will get the same result