I have duplicate records in one sql table . The rows has the same id but different values in different fields. how I can combine or merge those two rows or more into one row. Please help,
You can group those rows on certain fields by specifying a GROUP BY clause.
In your case you would group on the ID column. For the columns you select in the SELECT clause that are not specified in the GROUP BY clause (i.e. columns other than ID), you will have to apply an aggregate function (e.g. SUM, MAX, MIN, ...).
Edit - Simplified example based on your image:
SELECT
MasterID,
CUSTNAME=MIN(CUSTNAME),
ER1=MIN(ER1),
ER1_BU=MIN(ER1_BU)
-- For the other fields, the idea is the same
FROM
your_table
GROUP BY
MasterID
ORDER BY
MasterID;
This example takes for each field the minimum of the fields for a particular MasterID. You did not really define what you mean by "merge". Perhaps you want the result to be a particular merge, you will have to clarify further if this example doesn't "merge" the rows like you want.
Related
Why do I not get the same results when running the two queries? If I run the second one I get the course with the smallest amount of credits and when I run the first one I get the courses ordered by courseid
select min(credits), title, courseid
from course
group by title, courseid
select min(credits)
from course
An aggregation query is any query that has a group by or an aggregation function in the select.
An aggregation query returns one row per group, where a "group" is defined as the unique combination of values of the keys in the group by clause. If there is no group by clause, then all rows are taken to be a single group and one row is returned.
So, your first query returns one row for each combination of title and courseid in the course table. That row contains the minimum value of credits for that combination. If the course table has only one row per courseid, then the results are very similar to the contents of the table.
The second query returns one row overall, with the minimum number of credits of all rows.
If you want to get one row from with the minimum number of credits, then you don't want an aggregation query. Instead, you can use:
select c.*
from course c
order by c.credits
limit 1;
When you use a group by, you are using a sort of "filter", in the first query you group by title, then all the same titles are grouped by courseid, in the second you only select the minimum value of credits without filtering.
Take a look at a group by doc maybe with some graphical examples like this:
https://www.geeksforgeeks.org/sql-group-by/
Below is the data in my table:
TABLE:
abc-ac
abc-dc
aax-i
bcs-o-dc
ddd-o-poe-dc
I need to write a query which will display only the unique entries as a result:
abc-ac
aax-i
bcs-o-dc
ddd-o-poe-dc
So basically, since the first two entries start with "abc", it should be treated as one and displayed.
Thanks.
If you're not picky about which one of the two abc-* records that it shows you can use this:
SELECT f1 FROM mytable GROUP BY substring_index(f1, '-', 1)
SQLFiddle Here
That substring_index() function will split the value in your field by - and return the first bit. So essentially your records get grouped by only the first part. This is one of the few times that we can take advantage of MySQLs strange GROUP BY behavior where it will allow you to leave out non-aggregated fields from the group by.
I have a table :
CREATE TABLE data
(
value integer,
name varchar(100)
)
In my table there can be duplicate values of name possible with different value of value. Now I want to get DISTINCT name and there avg() value from the Table data.
I am able to get DISTINCT value of name but unable to get avg() of there values.
Now with following Query I get avg() of all data :
select floor(avg(value)) from data
I know this is incorrect but I am new to SQL. I want this select floor(avg(value)) for distinct values of name.
Data :
insert into data values(10, 'mnciitbhu')
insert into data values(20, 'mnciitbhu')
insert into data values(40, 'mafiya69')
insert into data values(20, 'mafiya69')
insert into data values(0, 'mafiya69')
Output :
mnciitbhu 15
mafiya69 20
Adding this because the other answers while accurate, are not detailed.
What you want to do here, are use the grouping and aggregation features of SQL.
grouping your results by particular fields, will divide your result set into discrete sections, which you can operate on with aggregate functions, to get averages, sums, counts etc, per group.
For a full list of aggregate functions, and other miscellaneous information about group by, you can read 12.16.1 GROUP BY (Aggregate) Functions.
In your instance, since you want the average per name, you will need to group by name. This would give the following query:
select name, avg(value)
from `data`
group by name; -- this is the important line
And this query will calculate the average of value, for each group of names in your table, returning one row per group.
One very important consideration when using group by, is that all fields contained in the select, must either be contained in the group by clause, or used in aggregate functions. If you refer to a field that isn't covered by this, you may end up with undesired indeterminate results.
From the manual 12.16.3 MySQL Handling of GROUP BY
MySQL extends the use of GROUP BY so that the select list can refer to
nonaggregated columns not named in the GROUP BY clause. This means
that the preceding query is legal in MySQL. You can use this feature
to get better performance by avoiding unnecessary column sorting and
grouping. However, this is useful primarily when all values in each
nonaggregated column not named in the GROUP BY are the same for each
group. The server is free to choose any value from each group, so
unless they are the same, the values chosen are indeterminate.
The importance of that paragraph cannot be overstated. It is very easy to mis-understand how this works, arrive at a query that seems to give the desired result, but will occasionally give incorrect/undesired data.
Use this code:
select name,AVG(value) as Average from data
group by name
order by name desc
OUTPUT:
name Average
mnciitbhu 15
mafiya69 20
Try this
select name,avg(value) from data group by name
I want to get the distinct value of a particular column however duplicity is not properly managed if more than 3 columns are selected.
The query is:
SELECT DISTINCT
ShoppingSessionId, userid
FROM
dbo.tbl_ShoppingCart
GROUP BY
ShoppingSessionId, userid
HAVING
userid = 7
This query produces correct result, but if we add another column then result is wrong.
Please help me as I want to use the ShoppingSessionId as a distinct, except when I want to use all the columns from the table, including with the where clause .
How can I do that?
The DISTINCT keyword applies to the entire row, never to a column.
Presently DISTINCT is not needed at all, because your script already makes sure that ShoppingSession is distinct: by specifying the column in GROUP BY and filtering on the other grouping column (userid).
When you add a third column to GROUP BY and it results in duplicated ShoppingSession, it means that some ShoppingSession values are associated with many different values of the added column.
If you want ShoppingSession to remain distinct after including that third column, you should decide which values of the the added column should be left in the output and which should be discarded. This is called aggregating. You could apply the MAX() function to that column, or MIN() or any other suitable aggregate function. Note that the column should not be included in GROUP BY in this case.
Here's an illustration of what I'm talking about:
SELECT
ShoppingSessionId,
userid,
MAX(YourThirdColumn) AS YourThirdColumn
FROM dbo.tbl_ShoppingCart
GROUP BY
ShoppingSessionId,
userid
HAVING userid = 7
There's one more note on your query. The HAVING clause is typically used for filtering on aggregated columns. If your filter does not involve aggregated columns, you'll be better off using the WHERE clause instead:
SELECT
ShoppingSessionId,
userid,
MAX(YourThirdColumn) AS YourThirdColumn
FROM dbo.tbl_ShoppingCart
WHERE userid = 7
GROUP BY
ShoppingSessionId,
userid
Although both queries would produce identical results, their efficiency would be different, because the first query would have to pull all rows, group/aggregate them, then discard all rows except userid = 7, but the second one would discard rows first and only then group/aggregate the remaining, which is much more efficient.
You could go even further and exclude the userid column from GROUP BY and pull its value with an aggregate function:
SELECT
ShoppingSessionId,
MAX(userid) AS userid,
MAX(YourThirdColumn) AS YourThirdColumn
FROM dbo.tbl_ShoppingCart
WHERE userid = 7
GROUP BY
ShoppingSessionId
Since all userid values in your output are supposed to contain 7 (because that's in your filter), you can just pick a maximum value per every ShoppingSession, knowing that it'll always be 7.
I have a "boolean" column in one of my tables (value is either 0 or 1).
I need to get two counts: The number of rows that have the boolean set to 0 and the number of rows that have it set to 1. Currently I have two queries: One to count the 1's and the other to count the 0's.
Is MySQL traversing the entire table when counting rows with a WHERE condition? I'm wondering if there's a single query that would allow two counters based on different conditions?
Or is there a way to get the total count along side the WHERE conditioned count? This would be enough as I'd only have to subtract one count from the other (due to the boolean nature of the column). There are no NULL values.
Thanks.
You could group your records by your boolean column and get count for each group.
SELECT bool_column, COUNT(bool_column) FROM your_table
WHERE your_conditions
GROUP BY bool_column
This will obviously work not only for bool columns but also with other data types if you need that.
Try this one:
SELECT
SUM(your_field) as positive_count,
SUM(IF(your_field, 0, 1)) as negative_count
FROM thetable
If they are all either 0 or 1 and you dont mind 2 rows as result you can group by that field and do a count like so:
select field, count(field)
from table
group by field
A simple group clause should do the trick :
SELECT boolField, COUNT(boolField)
FROM myTable
GROUP BY boolField