So my boss asked us to sort the columns alphabetically so the clients will have an easier time locating the column they want. The pictures below show what I mean by that.
Currently, the columns are shown in an order like this: original layout
However, what I am trying to achieve is like this: sorted columns
As you can see the columns are sorted alphabetically but I did that manually. I am trying to figure out a way to let the code do it. Even though it sounds like a fairly simple goal, it has taken me tons of time and all my approaches turn out to be nothing but dead ends. I am running my codes on Periscopedata.com and I think they use Redshift by Amazon.
The engineers at Periscopedata helped me a lot, and their approach is this:
CREATE TABLE #ordercolumns as SELECT attname::varchar as column_name
from pg_attribute WHERE attrelid='devices'::regclass::oid and
attnum>=1;
SELECT 'SELECT ' || LISTAGG(column_name, ',') within group (order by
column_name) || ' FROM devices' FROM #ordercolumns;
DROP TABLE #ordercolumns;
I was wondering if I could do something like:
select (select * from ordercolumns) from devices
Sorry if I didn't explain my questions well enough.
I wanna thank you guys ahead of time as this community has helped me tremendously since I was in college.
update: I wanna thank you for all your help. We try to avoid any type of manual sorting because we have hundreds of clients and each client has different columns they want to see. So sorting columns manually is going to take too long with very little accuracy. thank you
You could rearrange the order of the columns with something like this:
ALTER TABLE `devices`
CHANGE COLUMN content content VARCHAR(255) FIRST,
CHANGE COLUMN date date DATE AFTER `content`,
CHANGE COLUMN id id INT(11) AFTER `date`,
....
;
Just be sure to check the data types of each column and as always make a backup of the table before making any changes.
Related
Halo all.
I have a table with two columns. One of them with customer_id and another one with acceptence_reason. I want to delete the customer_id from the acceptance part but have not yet come up with a effective way to do so.
To avoid confusion I have added a picture to clearify my problem
I suppose you already tried substr() but maybe you didn't know instr(). So I would try that:
select Customer_id, substr(acceptance_reason, 0, instr(acceptance_reason,"(") ) as acceptance_reason from ...
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?"
I have a very large number of rows in my table, table_1. Sometimes I just need to retrieve a particular row.
I assume, when I use SELECT query with WHERE clause, it loops through the very first row until it matches my requirement.
Is there any way to make the query jump to a particular row and then start from that row?
Example:
Suppose there are 50,000,000 rows and the id which I want to search for is 53750. What I need is: the search can start from 50000 so that it can save time for searching 49999 rows.
I don't know the exact term since I am not expert of SQL!
You need to create an index : http://dev.mysql.com/doc/refman/5.1/en/create-index.html
ALTER TABLE_1 ADD UNIQUE INDEX (ID);
The way I understand it, you want to select a row with id 53750. If you have a field named id you could do this:
SELECT * FROM table_1 WHERE id = 53750
Along with indexing the id field. That's the fastest way to do so. As far as I know.
ALTER table_1 ADD UNIQUE INDEX (<collumn>)
Would be a great first step if it has not been generated automatically. You can also use:
EXPLAIN <your query here>
To see which kind of query works best in this case. Note that if you want to change the where statement (anywhere in the future) but see a returning value in there it will be a good idea to put an index on that aswell.
Create an index on the column you want to do the SELECT on:
CREATE INDEX index_1 ON table_1 (id);
Then, select the row just like you would before.
But also, please read up on databases, database design and optimization. Your question is full of false assumptions. Don't just copy and paste our answers verbatim. Get educated!
There are several things to know about optimizing select queries like Range and Where clause Optimization, the documentation is pretty informative baout this issue, read the section: Optimizing SELECT Statements. Creating an index on the column you evaluate is very helpfull regarding performance too.
One possible solution You can create View then query from view. here is details of creating view and obtain data from view
http://www.w3schools.com/sql/sql_view.asp
now you just split that huge number of rows into many view (i. e row 1-10000 in one view then 10001-20000 another view )
then query from view.
I am pretty sure that any SQL database with a little respect for themselves does not start looping from the first row to get the desired row. But I am also not sure how they makes it work, so I can't give an exact answer.
You could check out what's in your WHERE-clause and how the table is indexed. Do you have a proper primary key? Like using a numeric data type for that. Do you have indexes on more columns, that is used in your queries?
There is also alot to concider when installing the database server, like where to put the data and log files, how much memory to give the server and setting the growth. There's a lot you can do to tune your server.
You could try and split your tables in partitions
More about alter tables to add partitions
Selecting from a specific partition
In your case you could create a partition on ID for every 50.000 rows and when you want to skip the first 50.000 you just select from partition 2. How to do this ies explained quite well in the MySQL documentation.
You may try simple as this one.
query = "SELECT * FROM tblname LIMIT 50000,0
i just tried it with phpmyadmin. WHERE the "50,000" is the starting row to look up.
EDIT :
But if i we're you i wouldn't use this one, because it will lapses the 1 - 49999 records to search.
Various incarnations of this question have been asked here before, but I thought I'd give it another shot.
I had a terrible database layout. A single entity (widget) was split into two tables:
CREATE TABLE widgets (widget_id int(10) NOT NULL auto_increment)
CREATE TABLE widget_data (
widget_id int(10),
field ENUM('name','size','color','brand'),
data TEXT)
this was less that ideal. if wanted to find widgets of a specific name, color and brand, i had to do a three-way join on the widget_data table. so I converted to the reasonable table type:
CREATE TABLE widgets (widget_id int(10) NOT NULL auto_increment,
name VARCHAR(32),size INT(3),color VARCHAR(16), brand VARCHAR(32))
This makes most queries much better. But it makes searching harder. It used to be that if i wanted to search widgets for, say, '%black%', I would just SELECT * FROM widget_data WHERE data LIKE '%black%'. This would give me all instances of widgets that are black in color, or are made by blackwell industries, or whatever. I would even know exactly which field matched, and could show that to my user.
how do I execute a similar search using the new table layout? I could of course do WHERE name LIKE '%black%' OR size LIKE '%black%'... but that seems clunky, and I still don't know which fields matched. I could run a separate query for each column I want to match on, which would give me all matches and how they matched, but that would be a performance hit. any ideas?
You can include part of WHERE expression into selecting columns. For example:
SELECT
*,
(name LIKE '%black%') AS name_matched,
(size LIKE '%black%') AS size_matched
FROM widget_data
WHERE name LIKE '%black%' OR size LIKE '%black%'...
Then check value of name_matched on side of the script.
Not sure how it will affect performance. Feal free to test it before going to production
You have two conflicting requirements. You want to search as if all your data is in a single field, but you also want to identify which specific field was matched.
There's nothing wrong with your WHERE name LIKE '%black%' OR size LIKE '%black%'... expression. It's a perfectly valid search on the table as you have defined it. Why not just check the results in code to see which one matched? It's a minimal overhead.
If you want a cleaner syntax for your SQL then you could create a view on the table, adding an extra field which consists of concatenating the other fields:
CREATE VIEW extra_widget_data AS
SELECT (name, size, color, brand,
CONCAT(name, size, color, brand) as all_fields)
FROM widget_data;
Then you'd have to add an index on this field, which requires more space, CPU time to maintain etc. I don't think it's worth it.
You probably want to look into MySQL full text search capability, this enables you to match against multiple columns of varchar type.
http://dev.mysql.com/doc/refman/5.1/en/fulltext-search.html
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