I want to pull specific rows from a table where the date matches a certain date. First I'm converting the date string to date format, here's the query:
SELECT id, str_to_date(candidate.AddDate,"%d/%m/%Y") n FROM candidate WHERE n='2016-01-01';
But I get the error "Unknown column 'n' in WHERE clause"
How do I make the query use the result of str_to_date in the where clause?
You cant use the alias on the same level, because isnt created at that time
SELECT id,
Str_to_date(candidate.adddate, "%d/%m/%y") n
FROM candidate
WHERE Str_to_date(candidate.adddate, "%d/%m/%y") = '2016-01-01';
Or create a subquery
SELECT *
FROM (
SELECT id,
Str_to_date(candidate.adddate, "%d/%m/%y") n
FROM candidate
) T
WHERE n = '2016-01-01';
I dont know if this is what you are trying to achieve.
SELECT id, adddate from candidate C where C.adddate = "2016-01-01"
Why cant you pull all the table rows where the given date is 2016-01-01. Is this what you want? Or something else. If you have stored the date as date field you dont really need to do str_to_time.
If it is stored as string then
SELECT * FROM ( SELECT id, DATE_FORMAT(STR_TO_DATE(candidate.adddate, '%d/%m/%Y') x FROM candidate
) C WHERE x = '2016-01-01';
Related
I have a database with over 100,000 records. I'm trying to get all customers who ordered only once searching by customer's email field (OrderEmail).
The SQL query is running for 10 minutes and then times out.
If I use short date ranges, I can get results but it still takes over 3 minutes.
How can I optimize the syntax to get it work?
SELECT
tblOrders.OrderID,
tblOrders.OrderName,
tblOrders.OrderEmail,
tblOrders.OrderPhone,
tblOrders.OrderCountry,
tblOrders.OrderDate
FROM
tblOrders
LEFT JOIN tblOrders AS orders_join ON orders_join.OrderEmail = tblOrders.OrderEmail
AND NOT orders_join.OrderID = tblOrders.OrderID
WHERE
orders_join.OrderID IS NULL
AND (tblOrders.OrderDate BETWEEN '2015-01-01' AND '2017-03-01')
AND tblOrders.OrderDelivered = - 1
ORDER BY
tblOrders.OrderID ASC;
I would expect the below to work - but I can't test it as you don't provide sample data. Well, I added a temporary table definition that could be used for the query ....
But , if you could actually change the data model to use an INTEGER id for the entity who placed the order (instead of a VARCHAR() email address), you would get considerably faster.
CREATE TEMPORARY TABLE IF NOT EXISTS
tblorders(orderid,ordername,orderemail,orderphone,ordercountry,orderdate) AS (
SELECT 1,'ORD01','adent#hog.com' ,'9-991' ,'UK', DATE '2017-01-01'
UNION ALL SELECT 2,'ORD02','tricia#hog.com','9-992' ,'UK', DATE '2017-01-02'
UNION ALL SELECT 3,'ORD03','ford#hog.com' ,'9-993' ,'UK', DATE '2017-01-03'
UNION ALL SELECT 4,'ORD04','zaphod#hog.com','9-9943','UK', DATE '2017-01-04'
UNION ALL SELECT 5,'ORD05','marvin#hog.com','9-9942','UK', DATE '2017-01-05'
UNION ALL SELECT 6,'ORD06','ford#hog.com' ,'9-993' ,'UK', DATE '2017-01-06'
UNION ALL SELECT 7,'ORD07','tricia#hog.com','9-992' ,'UK', DATE '2017-01-07'
UNION ALL SELECT 8,'ORD08','benji#hog.com' ,'9-995' ,'UK', DATE '2017-01-08'
UNION ALL SELECT 9,'ORD09','benji#hog.com' ,'9-995' ,'UK', DATE '2017-01-09'
UNION ALL SELECT 10,'ORD10','ford#hog.com' ,'9-993' ,'UK', DATE '2017-01-10'
)
;
SELECT
tblOrders.OrderID
, tblOrders.OrderName
, tblOrders.OrderEmail
, tblOrders.OrderPhone
, tblOrders.OrderCountry
, tblOrders.OrderDate
FROM tblOrders
JOIN (
SELECT
OrderEmail
FROM tblOrders
GROUP BY
OrderEmail
HAVING COUNT(*) = 1
) singleOrders
ON singleOrders.OrderEmail = tblOrders.OrderEmail
ORDER BY OrderID
;
OrderID|OrderName|OrderEmail |OrderPhone|OrderCountry|OrderDate
1|ORD01 |adent#hog.com |9-991 |UK |2017-01-01
4|ORD04 |zaphod#hog.com|9-9943 |UK |2017-01-04
5|ORD05 |marvin#hog.com|9-9942 |UK |2017-01-05
As you can see, it returns Mr. Dent, Zaphod and Marvin, who all occur only once in the example data.
Another approach that might work is that you group by email address and get only those with one entry. It may behave unpredictably if you want to get customers with multiple orders but it should be fine for this particular case:
SELECT
tblOrders.OrderID,
tblOrders.OrderName,
tblOrders.OrderEmail,
tblOrders.OrderPhone,
tblOrders.OrderCountry,
tblOrders.OrderDate,
count(tblOrders.OrderID) as OrderCount
FROM
tblOrders
WHERE
tblOrders.OrderDate BETWEEN '2015-01-01' AND '2017-03-01'
AND tblOrders.OrderDelivered = - 1
GROUP BY
tblOrders.OrderEmail
HAVING
OrderCount = 1
ORDER BY
tblOrders.OrderID ASC;
Also, I suspect that if you're seeing so long query times with just 100k records, you probably don't have an index on the OrderEmail column - I suggest setting that up and that might help with your original queries as well.
This does not work in Oracle, or SQL Server but it does work in MySQL and SQLite. So, while the code is not portable between different RDBMS, it works for this particular case.
I have a table "T" that contains Date as one of the column.
In the table, there are multiple rows associated with single date entry.
I want an query that will give me all the rows associated with the latest date available in the table.
select * from table_name where date = (select max(date) from table_name);
If the column type is datetime then use this query
SELECT * FROM T
WHERE CAST(<DateColumn> AS DATE) = (SELECT MAX(cast(<DateColumn> AS DATE)) FROM T)
and if column type is just date then use this query
SELECT * FROM T
WHERE <DateColumn> = (SELECT MAX(<DateColumn>) FROM T)
Group function Max when used on date it results in latest date.
SELECT <<Columns from table>> T where date = (select max(date) from T);
I'm trying to execute a query like this:
SELECT MAX(counter), MIN(counter) ,
my_date IN (SELECT my_date FROM my_table WHERE counter = MAX(counter) ) AS max_Date ,
my_date IN (SELECT my_date FROM my_table WHERE counter = MIN(counter) ) AS min_Date
FROM my_table;
and it's giving me the "invalid use of group function" error. what I want to do is to find the date for the maximum counter and then find the date for the minimum counter. Any help!! really appreciate it .. thanks.
You're trying to use the result of aggregate functions (max()/min()) on a row-by-row basis, but those results are not available until the DB has scanned the entire table.
e.g. it's a chicken and egg problem. You need to count chickens, but the eggs that will produce the chickens haven't even been layed yet.
That's why there's HAVING clauses, which allow you to use the results of aggregate functions to do filtering.
Try this for the subqueries:
SELECT my_date FROM my_table HAVING counter = MIN(counter)
^^^^^^
You can get the dates where the largest and smallest counter values appear using a trick with group_concat() and substring_index():
SELECT MAX(counter), MIN(counter) ,
substring_index(group_concat(my_date order by counter desc), ',', 1) as max_date,
substring_index(group_concat(my_date order by counter), ',', 1) as min_date
FROM my_table;
Note: You probably want to format the date first to your liking.
You can also do this with a join.
The problem with your query is:
where counter = min(counter)
You can't include aggregation functions in the where clause, because both are referring to the table in the subquery. You could possibly do this using aliaes, but why bother? There are other ways to write the query.
You need a subselect to get the max and min counters and then join back against the table a couple of times to get the other values from those rows.
SELECT MaxCounter, MinCounter, a.my_date, b.my_date
FROM (SELECT MAX(counter) AS MaxCounter, MIN(counter) AS MinCounter
FROM my_table) Sub1
INNER JOIN my_table a ON Sub1.MaxCounter
INNER JOIN my_table b ON Sub1.MinCounter
Note that this does assume that counter is unique!
I have 2 tables both containing an event and date column. Is there a way to combine the results of both column's event field into one and sort them by their date field. That way only a single (and combined) event is returned instead of 2.
SELECT event,date FROM table1
UNION
SELECT event,date FROM table2 ORDER BY date
When using UNION you use ORDER by at bottom query it will order marged query
You can't use it except bottom query anyway it should throw an error
SELECT a.event, MAX(a.date) date
FROM
(
SELECT event, date FROM TableA
UNION
SELECT event, date FROM TableB
) a
GROUP BY a.event
ORDER BY a.date DESC
i have a table like this:
name date time
tom | 2011-07-04 | 01:09:52
tom | 2011-07-04 | 01:09:52
mad | 2011-07-04 | 02:10:53
mad | 2009-06-03 | 00:01:01
i want oldest name first:
SELECT *
ORDER BY date ASC, time ASC
GROUP BY name
(->doesn't work!)
now it should give me first mad(has earlier date) then tom
but with GROUP BY name ORDER BY date ASC, time ASC gives me the newer mad first because it groups before it sorts!
again: the problem is that i can't sort by date and time before i group because GROUP BY must be before ORDER BY!
Another method:
SELECT *
FROM (
SELECT * FROM table_name
ORDER BY date ASC, time ASC
) AS sub
GROUP BY name
GROUP BY groups on the first matching result it hits. If that first matching hit happens to be the one you want then everything should work as expected.
I prefer this method as the subquery makes logical sense rather than peppering it with other conditions.
As I am not allowed to comment on user1908688's answer, here a hint for MariaDB users:
SELECT *
FROM (
SELECT *
ORDER BY date ASC, time ASC
LIMIT 18446744073709551615
) AS sub
GROUP BY sub.name
https://mariadb.com/kb/en/mariadb/why-is-order-by-in-a-from-subquery-ignored/
I think this is what you are seeking :
SELECT name, min(date)
FROM myTable
GROUP BY name
ORDER BY min(date)
For the time, you have to make a mysql date via STR_TO_DATE :
STR_TO_DATE(date + ' ' + time, '%Y-%m-%d %h:%i:%s')
So :
SELECT name, min(STR_TO_DATE(date + ' ' + time, '%Y-%m-%d %h:%i:%s'))
FROM myTable
GROUP BY name
ORDER BY min(STR_TO_DATE(date + ' ' + time, '%Y-%m-%d %h:%i:%s'))
This worked for me:
SELECT *
FROM your_table
WHERE id IN (
SELECT MAX(id)
FROM your_table
GROUP BY name
);
Use a subselect:
select name, date, time
from mytable main
where date + time = (select min(date + time) from mytable where name = main.mytable)
order by date + time;
If you wont sort by max date and group by name, you can do this query:
SELECT name,MAX(date) FROM table group by name ORDER BY name
where date may by some date or date time string. It`s response to you max value of date by each one name
Another way to solve this would be with a LEFT JOIN, which could be more efficient. I'll first start with an example that considers only the date field, as probably it is more common to store date + time in one datetime column, and I also want to keep the query simple so it's easier to understand.
So, with this particular example, if you want to show the oldest record based on the date column, and assuming that your table name is called people you can use the following query:
SELECT p.* FROM people p
LEFT JOIN people p2 ON p.name = p2.name AND p.date > p2.date
WHERE p2.date is NULL
GROUP BY p.name
What the LEFT JOIN does, is when the p.date column is at its minimum value, there will be no p2.date with a smaller value on the left join and therefore the corresponding p2.date will be NULL. So, by adding WHERE p2.date is NULL, we make sure to show only the records with the oldest date.
And similarly, if you want to show the newest record instead, you can just change the comparison operator in the LEFT JOIN:
SELECT p.* FROM people p
LEFT JOIN people p2 ON p.name = p2.name AND p.date < p2.date
WHERE p2.date is NULL
GROUP BY p.name
Now, for this particular example where date+time are separate columns, you would need to add them in some way if you want to query based on the datetime of two columns combined, for example:
SELECT p.* FROM people p
LEFT JOIN people p2 ON p.name = p2.name AND p.date + INTERVAL TIME_TO_SEC(p.time) SECOND > p2.date + INTERVAL TIME_TO_SEC(p2.time) SECOND
WHERE p2.date is NULL
GROUP BY p.name
You can read more about this (and also see some other ways to accomplish this) on the The Rows Holding the Group-wise Maximum of a Certain Column page.
I had a different variation on this question where I only had a single DATETIME field and needed a limit after a group by or distinct after sorting descending based on the datetime field, but this is what helped me:
select distinct (column) from
(select column from database.table
order by date_column DESC) as hist limit 10
In this instance with the split fields, if you can sort on a concat, then you might be able to get away with something like:
select name,date,time from
(select name from table order by concat(date,' ',time) ASC)
as sorted
Then if you wanted to limit you would simply add your limit statement to the end:
select name,date,time from
(select name from table order by concat(date,' ',time) ASC)
as sorted limit 10
In Oracle, This work for me
SELECT name, min(date), min(time)
FROM table_name
GROUP BY name
work for me mysql
select * from (SELECT number,max(date_added) as datea FROM sms_chat group by number) as sup order by datea desc
This is not the exact answer, but this might be helpful for the people looking to solve some problem with the approach of ordering row before group by in mysql.
I came to this thread, when I wanted to find the latest row(which is order by date desc but get the only one result for a particular column type, which is group by column name).
One other approach to solve such problem is to make use of aggregation.
So, we can let the query run as usual, which sorted asc and introduce new field as max(doc) as latest_doc, which will give the latest date, with grouped by the same column.
Suppose, you want to find the data of a particular column now and max aggregation cannot be done.
In general, to finding the data of a particular column, you can make use of GROUP_CONCAT aggregator, with some unique separator which can't be present in that column, like GROUP_CONCAT(string SEPARATOR ' ') as new_column, and while you're accessing it, you can split/explode the new_column field.
Again, this might not sound to everyone. I did it, and liked it as well because I had written few functions and I couldn't run subqueries. I am working on codeigniter framework for php.
Not sure of the complexity as well, may be someone can put some light on that.
Regards :)