I've a database called test and i've tables called x,y,z.
How do i select x,y,z and there is a column called date IN X,Y,Z check whether there is a particular date.
Is there any build in function that does this?
update
SELECT column date from all tables which is in a database called test
Thanks in advance!!
As far as I know, in SQL you cannot 'select a table', you can select some
column(s) from one or many tables at once. The result of such a query is an another table (temporary table) that you retrieve the data from.
Please be more specific about what exactly you want to do (e.g.: "I want to select a column 'z' from table 'tableA' and column 'y' from table 'tableB'") - then I'm sure your question has a pretty simple answer :)
SELECT x.date AS x_date, y.date AS y_date, z.date AS z_date FROM x,y,z;
That produces a result:
+---------+---------+---------+
| x_date | y_date | z_date |
+---------+---------+---------+
| | | |
| | | |
+---------+---------+---------+
Alternatively you can get everything in one column by ussuing a query:
SELECT date FROM x
UNION ALL
SELECT date FROM y
UNION ALL
SELECT date FROM z;
That produces a result:
+-------+
| date |
+-------+
| |
| |
+-------+
In the example above you would get also duplicate values in the single column. If you want to avoid duplicates replace 'UNION ALL' with 'UNION'
I'm still not sure if I undestood what you really want ot achieve, but I still hope that helps
Also take a look at:
http://www.w3schools.com/sql/sql_union.asp
http://www.sql-tutorial.net/SQL-JOIN.asp
Related
How to retrieve odd rows from the table?
In the Base table always Cr_id is duplicated 2 times.
Base table
I want a SELECT statement that retrieves only those c_id =1 where Cr_id is always first as shown in the output table.
Output table
Just see the base table and output table you should automatically know what I want, Thanx.
Just testing min date should be enough
drop table if exists t;
create table t(c_id int,cr_id int,dt date);
insert into t values
(1,56,'2020-12-17'),(56,56,'2020-12-17'),
(1,8,'2020-12-17'),(56,8,'2020-12-17'),
(123,78,'2020-12-17'),(1,78,'2020-12-18');
select c_id,cr_id,dt
from t
where c_id = 1 and
dt = (select min(dt) from t t1 where t1.cr_id = t.cr_id);
+------+-------+------------+
| c_id | cr_id | dt |
+------+-------+------------+
| 1 | 56 | 2020-12-17 |
| 1 | 8 | 2020-12-17 |
+------+-------+------------+
2 rows in set (0.002 sec)
What you're looking for could be "partition by", at least if you're working on mssql.
(In the future, please include more background, SQL is not just SQL)
https://codingsight.com/grouping-data-using-the-over-and-partition-by-functions/
I have an old query lying around, that is able to put a sorting index on data who lacks this, although the underlying reason is 99.9% sure to be a bad data design.
Typically I use this query to remove bad data, but you may rewrite it to become a join instead, so that you can identify the data you need.
The reason why I'm not putting that answer here, is to point out, bad data design results in more work when reading it afterwards, whom seems to be the real root cause here.
DELETE t
FROM
(
SELECT ROW_NUMBER () OVER (PARTITION BY column_1 ,column_2, column_3 ORDER BY column_1,column_2 ,column_3 ) AS Seq
FROM Table
)t
WHERE Seq > 1
Edit: If it makes any difference, I am using mysql 5.7.19.
I have a table A, and am trying to randomly sample on average 10% of the rows. I have decided that using rand() in a subquery, and then filtering out on that random result would do the trick, but it is giving unexpected results. When I print out the randomly generated value after filtering, I get random values that do not match my main query's "where" clause, so I suppose it is regenerating the random value in the outer select.
I guess I'm missing something to do with subqueries and when things are executed, but I'm really not sure what's going on.
Can anyone explain what I might be doing wrong? I've checked out this post: In which sequence are queries and sub-queries executed by the SQL engine? , and my subquery is correlated so I assume that my subquery is being executed first, and then the main query is filtering off of it. Given my assumptions, I do not understand why the result has values that should have been filtered away.
Query:
select
*
from
(
select
*,
rand() as rand_value
from
A
) a_rand
where
rand_value < 0.1;
Result:
--------------------------------------
| id | events | rand_value |
--------------------------------------
| c | 1 | 0.5512495763145849 | <- not what I expected
--------------------------------------
I am not able to reproduce using this SQL Fiddle use that link and click the blue [Run SQL] button a few times
CREATE TABLE Table1
(`x` int)
;
INSERT INTO Table1
(`x`)
VALUES
(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)
;
Query 1:
select
*
from (
select
*
, rand() as rand_value
from Table1
) a_rand
where
rand_value < 0.1
[Results]:
| x | rand_value |
|---|---------------------|
| 1 | 0.03006686086772649 |
| 1 | 0.09353976332912199 |
| 1 | 0.08519635823107917 |
I have a column called "Permissions" in my table. The permissions are strings which can be:
"r","w","x","rw","wx","rwx","xwr"
etc. Please note the order of characters in the string is not fixed. I want to GROUP_CONCAT() on the "Permissions" column of my table. However this causes very large strings.
Example: "r","wr","wx" group concatenated is "r,wr,wx" but should be "r,w,x" or "rwx". Using distinct() clause doesn't seem to help much. I am thinking that if I could check if a permission value is a substring of the other column then I should not concatenate it, but I don't seem to find a way to accomplish that.
Any column based approach using solely string functions would also be appreicated.
EDIT:
Here is some sample data:
+---------+
| perm |
+---------+
| r,x,x,r |
| x |
| w,rw |
| rw |
| rw |
| x |
| w |
| x,x,r |
| r,x |
+---------+
The concatenated result should be:
+---------+
| perm |
+---------+
| r,w,x |
+---------+
I don't have control over the source of data and would like not to create new tables ( because of restricted privileges and memory constraints). I am looking for a post-processing step that converts each column value to the desired format.
A good idea would be to first normalize your data.
You could, for example try this way (I assume your source table is named Files):
Create simple table called PermissionCodes with only column named Code (type of string).
Put r, w, and x as values into PermissionCodes (three rows total).
In a subquery join Files to PermissionCodes on a condition that Code exists as a substring in Permissions.
Perform your GROUP_CONCAT aggregation on the result of the subquery.
If it is a case here, that for the same logical entires in Files there exists multiple permission sets that overlaps (i.e. for some file there is a row with rw and another row with w) then you would limit your subquery to distinct combinations of Files' keys and Code.
Here's a fiddle to demonstrate the idea:
http://sqlfiddle.com/#!9/6685d6/4
You can try something like:
SELECT user_id, GROUP_CONCAT(DISTINCT perm)
FROM Permissions AS p
INNER JOIN (SELECT 'r' AS perm UNION ALL
SELECT 'w' UNION ALL
SELECT 'x') AS x
ON p.permission LIKE CONCAT('%', x.perm, '%')
GROUP BY user_id
You can include any additional permission code in the UNION ALL of the derived table used to JOIN with Permissions table.
Demo here
I'm a bit of a newby at SQL and I don't really understand what to do here, so any help is really appreciated. I have a table full of readings from different readers, there's like 500.000 of them, so I can't do this by hand.
I received the table without the difference in it. I managed to calculate it, but there's a bit of a problem there...
It looks a bit like this:
reader_id | date | reading | difference
1 | 01-01-2013 | 205 | 0
1 | 02-01-2013 | 210 | 5
1 | 03-01-2013 | 213 | 3
... | ... | ... | ...
1 | 31-12-2013 | 2451 | 4
2 | 01-01-2013 | 8543 | 6092
2 | 02-01-2013 | 8548 | 5
reader_id and date form the primary key. The combination is unique.
How can I make sure I don't get the difference calculated when the last column contained a different reader_id?
When querying my data with a query like this one, the data get skewed by the incorrect difference between the two reader_ids:
SELECT AVG(difference), reader_id FROM table GROUP BY reader_id
For
I just want to get the average difference for each reader.
your query is perfectly good. I think you got something wrong in your difference calculation. The first value for reader_id=2, 6092, is the difference of the last reading from reader1 and the first reading from reader 2, i don't think that makes sense. If i'm not mistaken, the difference value is the current day reading - previous day reading. Therefore you should set the difference value of the first reading of each reader to 0.
You can do this with the following query:
UPDATE table t INNER JOIN (SELECT reader_id, min(date) as first_day FROM table GROUP BY reader_id) as tmp ON tmp.reader_id=t.reader_id AND tmp.first_day=t.date SET t.difference=0
Then
SELECT AVG(difference), reader_id FROM table GROUP BY reader_id
will do what you expect.
If you simply want the average difference, you can use the following query:
SELECT
meter_id,
MAX(reading) - MIN(reading) / COUNT(*) average_difference
FROM table
GROUP BY meter_id
ORDER BY meter_id;
It works on the logic that the the total difference for a given meter_id should be equal to MAX(reading) - MIN(reading).
I have a table, user_quotes, with the fields quotes_id, quotes_user, quotes_desc, quotes_date, quotes_status, and quotes_location. In this quotes_user allows duplication entries. When I execute my query I am trying to avoid duplication entries of quotes_user. So I executed the query like this,
select distinct quotes_user from user_quotes;
This query returns only the quotes_user field. How can I retrieve all other records using distinct quotes_user.
I have tried with these following,
select distinct quotes_user, quotes_desc, quotes_date, quotes_status from user_quotes;
It's not avoiding the duplication of quotes_user.
If I use,
select distinct quotes_user, * from user_quotes;
I am getting mysql error,
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '* FROM user_quotes.
How can I fetch all records using select distinct of a single column in a same table? I am storing the email address in the field. The datatype is varchar.
Note: please don't suggest me other types like group by or other. I need to know how I can retrieve the records by only using distinct.
In addition to what has already been said, it should be stressed that the DISTINCT keyword can't give you distinct results for an individual column when you're selecting multiple columns. You will get distinct rows of, in your case, 4 columns. What you're observing is the expected, standard behaviour of DISTINCT.
You say you want to retrieve the other fields, but you haven't specified how SQL is to know which values to retrieve for the other fields, for each distinct value of quotes_user.
To show you want I mean, consider this example:
+-------------+---------------+
| quotes_user | email_address |
+-------------+---------------+
| user1 | email1 |
| user1 | email2 |
| user2 | email3 |
| user2 | email4 |
| user2 | email5 |
| user3 | email6 |
+-------------+---------------+
Now, if you just wanted quotes_user, the output would obviously be:
+-------------+
| quotes_user |
+-------------+
| user1 |
| user2 |
| user3 |
+-------------+
But if you wanted the other fields as well, you'd need to decide whether, for example, to have email1 or email2 for the user1 row.
Perhaps what you want is to concatenate the values of the other fields together. In that case, I would suggest using the GROUP_CONCAT aggregate function with GROUP BY quotes_user.
I'm not sure why you want to avoid using GROUP BY, though. Perhaps if you could explain that, we could help more.
It sounds like quotes_user should be a foreign key like user_id to presumably your users table. You could then query user_quotes by user_id returning all the quotes for that user. Your front end could then format all the quotes for each user nicely, it doesn't really sound like a MySql issue.