SELECT E.flmavailable_date,E.flmavailable_num_licenses, flmavailable_product AS SERVER
FROM (SELECT flmavailable_num_licenses,flmavailable_date
FROM licenses_available
ORDER BY flmavailable_num_licenses ASC) E
WHERE flmavailable_product <= 4;
Error:---Unknown column 'flmavailable_product' in 'field list'
Even though there is field called by that name I am getting error.
I need help to resolve this
Your outer select is trying to select a flmavailable_product from your inner select, yet there is no such field in that inner query.
Can you include the schema of the licenses_available table and a description of what your query is intended to return? This would make it easier to help you. Based on your query as it stands, it seems like you might not need that inner subquery.
You need to include the flmavailable_product field in the inner sub query if it is a column in the licences_available table, or join to the appropriate table which contains this field in the inner query :
SELECT E.flmavailable_date,E.flmavailable_num_licenses,flmavailable_product AS SERVER
FROM (SELECT flmavailable_num_licenses,flmavailable_date, flmavailable_product
FROM licenses_available ORDER BY flmavailable_num_licenses ASC)E
WHERE flmavailable_product <= 4;
Also, not sure why you are using the inner subquery as all it does is a straight select
This is the query you wanted to write.
SELECT flmavailable_num_licenses,flmavailable_date, flmavailable_product AS SERVER
FROM licenses_available
WHERE flmavailable_product <= 4
ORDER BY flmavailable_num_licenses ASC
General select query structure is:
SELECT a,b,c FROM `table`
WHERE x<=y
Here your inner query is acting as a table. However your inner query is returning only two columns: flmavailable_num_licenses & flmavailable_date.
In your outer query, you are getting an error as you are trying to select column 'flmavailable_product' which is not available in the table (Inner query).
This is clearly indicated by the error (Unknown column 'flmavailable_product' in 'field list') you are getting.
To solve this, you need to either select flmavailable_product in inner query or if it is not present there, use join to join the tables where required column is present.
Please provide table structure for exact query.
Related
What is the internal order of operations in a MySQL SELECT query and a relational query?
For instance, a SELECT query to a single table:
SELECT `name`
FROM `users`
WHERE `publication_count`>0
ORDER BY `publication_count` DESC
I know that at first all table fields are fetched and then only name field is left at the end. Does it happen before or after the condition in WHERE is applied? When is ORDER BY applied?
A relational query using two tables:
SELECT `users`.`name`, `post`.`text`
FROM `users`, `posts`
WHERE `posts`.`author_id`=`user`.`id`
ORDER BY `posts`.`date` DESC
Same question. What happens after what? (I know that at first the Cartesian product is generated)
Processing regarding your example simplifying the rules goes as follow:
1. FROM -- all elements in list (including multiple tables)
2. WHERE -- discard rows not matching conditions
3. SELECT -- output rows are computed (not fetched)
4. ORDER BY -- sort output rows
Also, you shouldn't be using old-fashioned implicit join syntax in WHERE condition. Instead, please use JOIN:
SELECT ...
FROM users
INNER JOIN posts ON users.id = posts.author_id
ORDER BY ...
The following query works just fine. I am using a value from the outer select to filter inside the inner select.
SELECT
bk.ID,
(SELECT COUNT(*) FROM guests WHERE BookingID = bk.ID) as count
FROM
bookings bk;
However, the following select will not work:
SELECT
bk.ID,
(SELECT SUM(count) FROM (SELECT COUNT(*) AS count FROM guests WHERE BookingID = bk.ID GROUP BY RoomID) sub) as sumcount
FROM
bookings bk;
The error message is: Error Code: 1054. Unknown column 'bk.ID' in 'where clause'
Why is my alias bk known in the subselect, but not in the subselect of the subselect?
For the record, I am using MySQL 5.6.
This is called "scoping". I know that Oracle (for instance) only looks out one level for resolving table aliases. SQL Server is also consistent: it looks out more than one level.
Based on this example, MySQL clearly limits the scope of the identifier bk to the immediate subquery. There is a small hint in the documentation (emphasis mine):
A correlated subquery is a subquery that contains a reference to a
table that also appears in the outer query.
However, I have not found any other specific reference to the scoping rules in the documentation. There are other answers (here and here) that specify that the scope of a table alias is limited to one level of subquery.
You already know how to fix the problem (your two queries should produce identical results). Re-arranging the query to have joins and aggregations can also resolve this problem.
Correlated Scalar Subqueries in the SELECT list can usually be rewritten to a LEFT JOIN on a Derived Table (and in many cases they might perform better then):
SELECT
bk.ID,
dt.sumcount
FROM
bookings bk
LEFT JOIN
(SELECT BookingID,SUM(COUNT) AS sumcount
FROM
(
SELECT BookingID, RoomId, COUNT(*) AS COUNT
FROM guests
GROUP BY BookingID, RoomID
) sub
) AS dt
ON bk.BookingID = dt.BookingID
I am using the below code..
SELECT
a.auction_id,
a.name,
media.media_id
FROM
auctions AS a
LEFT JOIN users AS u ON u.user_id=a.owner_id
INNER JOIN (SELECT media_url
FROM auction_media
ORDER BY media_id ASC
LIMIT 1) AS media ON a.auction_id=media.auction_id
WHERE
............
However I am getting errors such as Unknown column 'media.media_id' in 'field list'
or Unknown column 'media.auction_id' in 'on clause' - why is this?
I am sure I have used similar queries before without any problems like this.
Edit: Just tested my other query where I do something similar and I was using * as the field select. Seems I can't reference the joined sub-query table though.
Hi i have this query but its giving me an error of Operand should contain 1 column(s) not sure why?
Select *,
(Select *
FROM InstrumentModel
WHERE InstrumentModel.InstrumentModelID=Instrument.InstrumentModelID)
FROM Instrument
according to your query you wanted to get data from instrument and instrumentModel table and in your case its expecting "from table name " after your select * .when the subselect query runs to get its result its not finding table instrument.InstrumentModelId inorder to fetch result from both the table by matching you can use join .or you can also select perticuler fields by tableName.fieldName and in where condition use your condition.
like :
select Instrument.x,InstrumentModel.y
from instrument,instrumentModel
where instrument.x=instrumentModel.y
You can use a join to select from 2 connected tables
select *
from Instrument i
join InstrumentModel m on m.InstrumentModelID = i.InstrumentModelID
When you use subqueries in the column list, they need to return exactly one value. You can read more in the documentation
as a user commented in the documentation, using subqueries like this can ruin your performance:
when the same subquery is used several times, mysql does not use this fact to optimize the query, so be careful not to run into performance problems.
example:
SELECT
col0,
(SELECT col1 FROM table1 WHERE table1.id = table0.id),
(SELECT col2 FROM table1 WHERE table1.id = table0.id)
FROM
table0
WHERE ...
the join of table0 with table1 is executed once for EACH subquery, leading to very bad performance for this kind of query.
Therefore you should rather join the tables, as described by the other answer.
i am trying to run a join query on mysql i am using following query:
SELECT `Reservation`.`id`
FROM `reservations` AS `Reservation`
LEFT JOIN rates ON Reservation.postal_code=rates.postal_code
this gives my results only for "Reservation" table, and no results for the "rates" table at all, but the following query works fine
SELECT `Reservation`.`id`, rates.id
FROM `reservations` AS `Reservation`, rates
WHERE Reservation.postal_code = rates.postal_code
i am unsure what am i doing wrong, can someone please help?
edit
I was using cakephp and this is just a modified version of a query generated by cakephp and it didnt specify the fields in "select" case so i thought it isn't needed.
You have to include them in the SELECT
SELECT `Reservation`.`id`, rates.*
FROM `reservations` AS `Reservation`
LEFT JOIN rates ON Reservation.postal_code=rates.postal_code
In your second query you have rates.id, that is including it.
NOTE: Don't use the kind of join from the second query you showed us. That's a cross join (theta join) and will make your query go really slow. Always use JOINS.
The first query returns only a single column, id, from reservations. Are you expecting to see data from rates as well? You must mention those columns after the keyword SELECT.
The second query includes the column id from rates.
If you modify the queries so they return the same list of columns they will produce similar (but not identical results). They will still differ in that the second query may return fewer rows — it will not include reservations with 0 corresponding rates (because it uses an INNER JOIN).
The first query isn't selecting from the Rates table. Try this:
SELECT `Reservation`.`id`, `rates`.`id`
FROM `reservations` AS `Reservation`
LEFT JOIN rates ON Reservation.postal_code=rates.postal_code