


MySQL "Operand Should Contain 1 Column" Error in NOT IN
Subqueries with Aggregate Functions
Using NOT IN
subqueries in MySQL requires careful attention to column counts. A common error, "Operand should contain 1 column," arises when the subquery uses aggregate functions like COUNT()
, returning multiple columns. MySQL's NOT IN
operator expects a single-column comparison.
Root Cause:
The error stems from a mismatch in the number of columns returned by the main query and the subquery. The NOT IN
subquery, containing an aggregate function, produces a result set with more than one column, conflicting with the single-column id
in the main query's WHERE
clause.
Illustrative Example:
Consider this problematic query:
SELECT * FROM campaigns WHERE id NOT IN ( SELECT e.id_campaign, d.name, d.frequency, d.country, d.referral, d.bid, d.status, COUNT(e.id) AS countcap FROM campaigns d LEFT JOIN served e ON d.id = e.id_campaign WHERE d.status = 'Active' GROUP BY e.id_campaign HAVING countcap < p>The intention is to select campaigns *not* included in the subquery's results. The subquery, however, returns eight columns, causing the "Operand should contain 1 column" error because `NOT IN` expects a single-column comparison against the `id` column in the `campaigns` table.</p><p>**Resolution:**</p><p>The solution involves restructuring the subquery to return only the `id_campaign` column:</p><pre class="brush:php;toolbar:false"><code class="language-sql">SELECT * FROM campaigns WHERE id NOT IN ( SELECT e.id_campaign FROM campaigns d LEFT JOIN served e ON d.id = e.id_campaign WHERE d.status = 'Active' GROUP BY e.id_campaign HAVING COUNT(e.id) <
Alternatively, for situations requiring multiple columns, use `EXISTS` or `NOT EXISTS` for a more efficient and accurate solution:
SELECT * FROM campaigns c WHERE NOT EXISTS ( SELECT 1 FROM campaigns d INNER JOIN served e ON d.id = e.id_campaign WHERE d.id = c.id AND d.status = 'Active' AND COUNT(e.id) <
This revised approach avoids the column count mismatch and provides a cleaner solution for scenarios involving aggregate functions within subqueries used with `NOT IN`.
The above is the detailed content of Why Does My MySQL `NOT IN` Query with `COUNT()` Result in an 'Operand Should Contain 1 Column' Error?. For more information, please follow other related articles on the PHP Chinese website!

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