My question is as follows:
SELECT title, 'dossier' as Source FROM dossier
UNION ALL
SELECT title, 'contract' as Source FROM contract ORDER BY `time` LIMIT 5
time column is present in both tables, but MySQL throws the following error:
unknown column 'time' in 'order clause'
When I remove , 'dossier' as Source and , 'contract' as Source the query works correctly.
order by clause is applied on the union all overall selection here, which doesn't have the time column (only title and Source). What you can do is use a temporary table:
select `title`, `source` from (
select `title`, 'dossier' as `Source`, `time` from dossier
union all
select `title`, 'contract', `time` from contract
) tbl
order by `time`
limit 5
#Potashin has one method for solving this.
You should understand that the order by is not part of either select clause. It only knows about the columns that are being selected.
Another solution is easy enough . . . that is to simply include time in the result set. What is happening might be clearer if you use parentheses:
(SELECT title, 'dossier', time as Source
FROM dossier
)
UNION ALL
(SELECT title, 'contract', time as Source
FROM contract
)
ORDER BY `time`
LIMIT 5;
I should note that if the tables are large and they have indexes on time, then the following may be more efficient:
(SELECT title, 'dossier', time as Source
FROM dossier
ORDER BY `time`
LIMIT 5
)
UNION ALL
(SELECT title, 'contract', time as Source
FROM contract
ORDER BY `time`
LIMIT 5
)
ORDER BY `time`
LIMIT 5;
Related
I am trying to write a query for a condition:
If >=80 percent (4 or more rows as 4/5*100=80%) of the top 5 recent rows(by Date Column), for a KEY have Value =A or =B, then change the flag from fail to pass for the entire KEY.
Here is the input and output sample:
I have highlighted recent rows with green colour in the sample.
Can someone help me in this?
I tried till finding the top 5 recent rows by the foll code:
select * from(
select *, row_number() over (partition by "KEY") as 'RN' FROM (
select * from tb1
order by date desc))
where "RN"<=5
Couldnt figure what to be done after this
Test this:
WITH
-- enumerate rows per key group
cte1 AS ( SELECT *,
ROW_NUMBER() OVER (PARTITION BY `key` ORDER BY `date` DESC) rn
FROM sourcetable ),
-- take 5 recent rows only, check there are at least 4 rows with A/B
cte2 AS ( SELECT `key`
FROM cte1
WHERE rn <= 5
GROUP BY `key`
HAVING ( SUM(`value` = 'A') >= 4
OR SUM(`value` = 'B') >= 4 )
-- AND SUM(rn = 5) )
-- update rows with found key values
UPDATE sourcetable
JOIN cte2 USING (`key`)
SET flag = 'PASS';
5.7 version – Ayn76
Convert CTEs to subqueries. Emulate ROW_NUMBER() using user-defined variable.
Is it possible to order when the data comes from many select and union it together? Such as
In this statement, the vouchers data is not showing in the same sequence as I saved on the database, I also tried it with "ORDER BY v_payments.payment_id ASC" but won't be worked
( SELECT order_id as id, order_date as date, ... , time FROM orders WHERE client_code = '$searchId' AND order_status = 1 AND order_date BETWEEN '$start_date' AND '$end_date' ORDER BY time)
UNION
( SELECT vouchers.voucher_id as id, vouchers.payment_date as date, v_payments.account_name as name, ac_balance as oldBalance, v_payments.debit as debitAmount, v_payments.description as descriptions,
vouchers.v_no as v_no, vouchers.v_type as v_type, v_payments.credit as creditAmount, time, zero as tax, zero as freightAmount FROM vouchers INNER JOIN v_payments
ON vouchers.voucher_id = v_payments.voucher_id WHERE v_payments.client_code = '$searchId' AND voucher_status = 1 AND vouchers.payment_date BETWEEN '$start_date' AND '$end_date' ORDER BY v_payments.payment_id ASC , time )
UNION
( SELECT return_id as id, return_date as date, ... , time FROM w_return WHERE client_code = '$searchId' AND w_return_status = 1 AND return_date BETWEEN '$start_date' AND '$end_date' ORDER BY time)
Wrap the sub-select queries in the union within a SELECT
SELECT id, name
FROM
(
SELECT id, name FROM fruits
UNION
SELECT id, name FROM vegetables
)
foods
ORDER BY name
If you want the order to only apply to one of the sub-selects, use parentheses as you are doing.
Note that depending on your DB, the syntax may differ here. And if that's the case, you may get better help by specifying what DB server (MySQL, SQL Server, etc.) you are using and any error messages that result.
You need to put the ORDER BY at the end of the statement i.e. you are ordering the final resultset after union-ing the 3 intermediate resultsets
To use an ORDER BY or LIMIT clause to sort or limit the entire UNION result, parenthesize the individual SELECT statements and place the ORDER BY or LIMIT after the last one. See link below:
ORDER BY and LIMIT in Unions
(SELECT a FROM t1 WHERE a=10 AND B=1)
UNION
(SELECT a FROM t2 WHERE a=11 AND B=2)
ORDER BY a LIMIT 10;
Ok, so I have the following query:
SELECT MIN(`date`), `player_name`
FROM `player_playtime`
GROUP BY `player_name`
I then need to use this result inside the following query:
SELECT DATE(`date`) , COUNT(DISTINCT `player_name`)
FROM `player_playtime /*Use previous query result here*/`
GROUP BY DATE( `date`) DESC LIMIT 60
How would I go about doing this?
You just need to write the first query as a subquery (derived table), inside parentheses, pick an alias for it (t below) and alias the columns as well.
The DISTINCT can also be safely removed as the internal GROUP BY makes it redundant:
SELECT DATE(`date`) AS `date` , COUNT(`player_name`) AS `player_count`
FROM (
SELECT MIN(`date`) AS `date`, `player_name`
FROM `player_playtime`
GROUP BY `player_name`
) AS t
GROUP BY DATE( `date`) DESC LIMIT 60 ;
Since the COUNT is now obvious that is only counting rows of the derived table, you can replace it with COUNT(*) and further simplify the query:
SELECT t.date , COUNT(*) AS player_count
FROM (
SELECT DATE(MIN(`date`)) AS date
FROM player_playtime
GROUP BY player_name
) AS t
GROUP BY t.date DESC LIMIT 60 ;
I have huge table with millions of records that store stock values by timestamp. Structure is as below:
Stock, timestamp, value
goog,1112345,200.4
goog,112346,220.4
Apple,112343,505
Apple,112346,550
I would like to query this table by timestamp. If the timestamp matches,all corresponding stock records should be returned, if there is no record for a stock for that timestamp, the immediate previous one should be returned. In the above ex, if I query by timestamp=1112345 then the query should return 2 records:
goog,1112345,200.4
Apple,112343,505 (immediate previous record)
I have tried several different ways to write this query but no success & Im sure I'm missing something. Can someone help please.
SELECT `Stock`, `timestamp`, `value`
FROM `myTable`
WHERE `timestamp` = 1112345
UNION ALL
SELECT `Stock`, `timestamp`, `value`
FROM `myTable`
WHERE `timestamp` < 1112345
ORDER BY `timestamp` DESC
LIMIT 1
select Stock, timestamp, value from thisTbl where timestamp = ? and fill in timestamp to whatever it should be? Your demo query is available on this fiddle
I don't think there is an easy way to do this query. Here is one approach:
select tprev.*
from (select t.stock,
(select timestamp from t.stock = s.stock and timestamp <= <whatever> order by timestamp limit 1
) as prevtimestamp
from (select distinct stock
from t
) s
) s join
t tprev
on s.prevtimestamp = tprev.prevtimestamp and s.stock = t.stock
This is getting the previous or equal timestamp for the record and then joining it back in. If you have indexes on (stock, timestamp) then this may be rather fast.
Another phrasing of it uses group by:
select tprev.*
from (select t.stock,
max(timestamp) as prevtimestamp
from t
where timestamp <= YOURTIMESTAMP
group by t.stock
) s join
t tprev
on s.prevtimestamp = tprev.prevtimestamp and s.stock = t.stock
Here is my query
SELECT file_id, file_name, file_date, file_email
FROM (SELECT *
FROM `file`
ORDER BY file_date DESC
) AS t
WHERE file_domains = ''
GROUP BY file_name
ORDER BY file_date DESC
LIMIT 0 , 100
primary key is file_id and index is file_name. Records about 900k
It took about 2 seconds in my local computer.
Is there any optimize for this query?
thanks in advance.
Your query uses a non-standard "feature" (mistake: one non-standard and one semi-standard feature) of MySQL and there is no guarantee that it will not break in future versions of MySQL, when the optimizer will be clever enough to understand that the subquery is redundant.
Add an index on (file_domains, file_name, file_date) and try this version:
SELECT f.file_id, f.file_name, f.file_date, f.file_email
FROM
`file` AS f
JOIN
( SELECT file_name
, MAX(file_date) AS max_file_date
FROM `file`
WHERE file_domains = ''
GROUP BY file_name
ORDER BY max_file_date DESC
LIMIT 0 , 100
) AS fm
ON fm.file_name = f.file_name
AND fm.max_file_date = f.file_date
ORDER BY f.file_date DESC ;
This intermediate query:
SELECT *
FROM `file`
ORDER BY file_date DESC
Fetches 900k records and orders by date, that might be slow.