


How to Fix \'Error 1222 (21000): The used SELECT statements have a different number of columns\' in MySQL UNION Operations?
Oct 29, 2024 am 01:41 AMError: Discordant Column Count in SELECT Statements
In MySQL, UNION and UNION ALL operations demand that the participating SELECT statements possess an identical number of columns within their SELECT clauses. Additionally, the data types of the columns must correspond at each position.
The provided query violates this rule:
<code class="sql">SELECT * FROM friends LEFT JOIN users AS u1 ON users.uid = friends.fid1 LEFT JOIN users AS u2 ON users.uid = friends.fid2 WHERE (friends.fid1 = 1) AND (friends.fid2 > 1) UNION SELECT fid2 FROM friends WHERE (friends.fid2 = 1) AND (friends.fid1 < 1) ORDER BY RAND() LIMIT 6;
The first SELECT statement returns all columns from the "friends" and "users" tables, while the second SELECT statement returns only the "fid2" column from the "friends" table. This discrepancy in column count leads to the following error message:
<code class="error">ERROR 1222 (21000): The used SELECT statements have a different number of columns from the following:
To resolve the error, ensure that all SELECT statements in the UNION operation have the same number of columns. The easiest way to achieve this is by using an explicit column list in each SELECT statement:
<code class="sql">SELECT f.*, u.* FROM FRIENDS AS f JOIN USERS AS u ON u.uid = f.fid2 WHERE f.fid1 = 1 AND f.fid2 > 1 UNION SELECT f.*, u.* FROM FRIENDS AS f JOIN USERS AS u ON u.uid = f.fid1 WHERE f.fid2 = 1 AND f.fid1 < 1 ORDER BY RAND() LIMIT 6;</code>
By explicitly specifying the columns in each SELECT statement, MySQL can ensure that the column count and data types match, allowing the UNION operation to proceed without error.
The above is the detailed content of How to Fix \'Error 1222 (21000): The used SELECT statements have a different number of columns\' in MySQL UNION Operations?. For more information, please follow other related articles on the PHP Chinese website!

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