MySQL - Operand should contain 1 column(s)

Question

While working on a system I'm creating, I attempted to use the following query in my project:

SELECT
topics.id,
topics.name,
topics.post_count,
topics.view_count,
COUNT( posts.solved_post ) AS solved_post,
(SELECT users.username AS posted_by,
    users.id AS posted_by_id
    FROM users
    WHERE users.id = posts.posted_by)
FROM topics
LEFT OUTER JOIN posts ON posts.topic_id = topics.id
WHERE topics.cat_id = :cat
GROUP BY topics.id

":cat" is bound by my PHP code as I'm using PDO. 2 is a valid value for ":cat".

That query though gives me an error: "#1241 - Operand should contain 1 column(s)"

What stumps me is that I would think that this query would work no problem. Selecting columns, then selecting two more from another table, and continuing on from there. I just can't figure out what the problem is.

Is there a simple fix to this, or another way to write my query?

Endpaper

Answer 1

Your subquery is selecting two columns, while you are using it to project one column (as part of the outer SELECT clause). You can only select one column from such a query in this context.

Consider joining to the users table instead; this will give you more flexibility when selecting what columns you want from users.

SELECT
topics.id,
topics.name,
topics.post_count,
topics.view_count,
COUNT( posts.solved_post ) AS solved_post,
users.username AS posted_by,
users.id AS posted_by_id

FROM topics

LEFT OUTER JOIN posts ON posts.topic_id = topics.id
LEFT OUTER JOIN users ON users.id = posts.posted_by

WHERE topics.cat_id = :cat
GROUP BY topics.id

Bioenergetics

Thanks for the response. I'll fix my query, and mark you as the answer, but just for input, do you think there's a "better" way to write my query than what I'm using now (but also disregarding the error in it)? – Endpaper

Ah. Thank you for the edit on your original post. I will be sure to mark you as the answer when StackOverflow lets me. Thanks a lot! – Endpaper

Well, the COUNT() is throwing things off a bit; the query I've given will probably give an error due to the aggregation. You may need to move that aggregation into a subquery, depending on the goals of your query (which are not clear to me at the moment). – Bioenergetics

Answer 2

In my case, the problem was that I sorrounded my columns selection with parenthesis by mistake:

SELECT (p.Column1, p.Column2, p.Column3) FROM Table1 p WHERE p.Column1 = 1;

And has to be:

SELECT p.Column1, p.Column2, p.Column3 FROM Table1 p WHERE p.Column1 = 1;

Sounds silly, but it was causing this error and it took some time to figure it out.

Frailty

I can't believe this is what my problem was, I thought brackets were legal there – Dominickdominie

Yes, this was my problem as well :) Thank you – Neanderthal

Yes, same problem here. SQL and parenthesis and single quote marks around fields can be confusing. – Intermolecular

Answer 3

This error can also occur if you accidentally use commas instead of AND in the ON clause of a JOIN:

JOIN joined_table ON (joined_table.column = table.column, joined_table.column2 = table.column2)
                                                        ^
                                             should be AND, not a comma

Turbit

That really saved me a lot of time. Thanks! – Difficile

Answer 4

This error can also occur if you accidentally use = instead of IN in the WHERE clause:

FOR EXAMPLE:

WHERE product_id = (1,2,3);

Osier

Or LIKE instead of IN as i did and couldnt find why this error happens. ty for pointer. – Universalism

It can also happen if you put brackets around the fields in the SELECT clause, e.g. SELECT (Field1, Field2) FROM Table – Valuation

Answer 5

COUNT( posts.solved_post ) AS solved_post,
(SELECT users.username AS posted_by,
    users.id AS posted_by_id
    FROM users
    WHERE users.id = posts.posted_by)

Well, you can’t get multiple columns from one subquery like that. Luckily, the second column is already posts.posted_by! So:

SELECT
topics.id,
topics.name,
topics.post_count,
topics.view_count,
posts.posted_by
COUNT( posts.solved_post ) AS solved_post,
(SELECT users.username AS posted_by_username
    FROM users
    WHERE users.id = posts.posted_by)
...

Tannen

Answer 6

I got this error while executing a MySQL script in an Intellij console, because of adding brackets in the wrong place:

WRONG:

SELECT user.id
FROM user
WHERE id IN (:ids); # Do not put brackets around list argument

RIGHT:

SELECT user.id
FROM user
WHERE id IN :ids; # No brackets is correct

Pollypollyanna

this does not match with the first answer here: #24551677 – Petit

@rubydio, that question references HQL and Hibernate, whereas my answer is referring to MySQL in an Intellij console – Pollypollyanna

@janac-meena thanks, i knew it, but when is already written i couldn't see the error – Shortwave

Answer 7

This error can also occur if you accidentally miss if function name.

for example:

set v_filter_value = 100;

select
    f_id,
    f_sale_value
from
    t_seller
where
    f_id = 5
    and (v_filter_value <> 0, f_sale_value = v_filter_value, true);

Got this problem when I missed putting if in the if function!

Salesgirl

Answer 8

Another place this error can happen in is assigning a value that has a comma outside of a string. For example:

SET totalvalue = (IFNULL(i.subtotal,0) + IFNULL(i.tax,0),0)

Polivy

Answer 9

(SELECT users.username AS posted_by,
users.id AS posted_by_id
FROM users
WHERE users.id = posts.posted_by)

Here you using sub-query but this sub-query must return only one column. Separate it otherwise it will shows error.

Prohibit

Answer 10

I also have the same issue in making a company database. this is the code

SELECT FNAME,DNO FROM EMP 
 WHERE SALARY IN (SELECT MAX(SALARY), DNO
FROM EMP GROUP BY DNO);

Godden

Answer 11

I also had this error message using Dapper with MySQL. Example code below:

SELECT ColA, ColB, ColC
FROM Table
WHERE ColA IN (@listOfColumns);

The issue with the above code is Dapper will automatically add the brackets for the @listOfColumns parameter substitution meaning the brackets in the snippet above will double wrap the list of columns causing the error.

Budde

Answer 12

In my code, I wrote in this way before:

@Query(value = "SELECT pr.id"
    + " FROM biz_project pr"
    + " LEFT JOIN sys_user u ON pr.create_user_id = u.id"
    + " LEFT JOIN sys_department de ON pr.department_id = de.id"
    + " WHERE :roleUsers IS NULL OR pr.create_user_id IN (:roleUsers)"
    + " AND :roleDepts IS NULL OR pr.department_id IN (:roleDepts)", 
nativeQuery = true)
List<Long> test(@Param("userIdList") List<Long> userIdList,
    @Param("deptIdList") List<Long> deptIdList);

It has the same error, SQL Error: 1241, SQLState: 21000 Operand should contain 1 column(s).

But I'll remove these two parts:':roleUsers IS NULL OR ' and ':roleDepts IS NULL OR', It can run normally and return the result I want. But I don't know why.

Entablature

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