#1222 - The used SELECT statements have a different number of columns - sql

Question

Why am i getting a #1222 - The used SELECT statements have a different number of columns
? i am trying to load wall posts from this users friends and his self.
SELECT u.id AS pid, b2.id AS id, b2.message AS message, b2.date AS date FROM
(
(
SELECT b.id AS id, b.pid AS pid, b.message AS message, b.date AS date FROM
wall_posts AS b
JOIN Friends AS f ON f.id = b.pid
WHERE f.buddy_id = '1' AND f.status = 'b'
ORDER BY date DESC
LIMIT 0, 10
)
UNION
(
SELECT * FROM
wall_posts
WHERE pid = '1'
ORDER BY date DESC
LIMIT 0, 10
)
ORDER BY date DESC
LIMIT 0, 10
) AS b2
JOIN Users AS u
ON b2.pid = u.id
WHERE u.banned='0' AND u.email_activated='1'
ORDER BY date DESC
LIMIT 0, 10
The wall_posts table structure looks like id date privacy pid uid message
The Friends table structure looks like Fid id buddy_id invite_up_date status
pid stands for profile id. I am not really sure whats going on.

Answer 1

The first statement in the UNION returns four columns:
SELECT b.id AS id,
b.pid AS pid,
b.message AS message,
b.date AS date
FROM wall_posts AS b
The second one returns six, because the * expands to include all the columns from WALL_POSTS:
SELECT b.id,
b.date,
b.privacy,
b.pid.
b.uid message
FROM wall_posts AS b
The UNION and UNION ALL operators require that:
The same number of columns exist in all the statements that make up the UNION'd query
The data types have to match at each position/column
Use:
FROM ((SELECT b.id AS id,
b.pid AS pid,
b.message AS message,
b.date AS date
FROM wall_posts AS b
JOIN Friends AS f ON f.id = b.pid
WHERE f.buddy_id = '1' AND f.status = 'b'
ORDER BY date DESC
LIMIT 0, 10)
UNION
(SELECT id,
pid,
message,
date
FROM wall_posts
WHERE pid = '1'
ORDER BY date DESC
LIMIT 0, 10))

Answer 2

You're taking the UNION of a 4-column relation (id, pid, message, and date) with a 6-column relation (* = the 6 columns of wall_posts). SQL doesn't let you do that.

Answer 3

(
SELECT b.id AS id, b.pid AS pid, b.message AS message, b.date AS date FROM
wall_posts AS b
JOIN Friends AS f ON f.id = b.pid
WHERE f.buddy_id = '1' AND f.status = 'b'
ORDER BY date DESC
LIMIT 0, 10
)
UNION
(
SELECT id, pid , message , date
FROM
wall_posts
WHERE pid = '1'
ORDER BY date DESC
LIMIT 0, 10
)
You were selecting 4 in the first query and 6 in the second, so match them up.

Answer 4

Beside from the answer given by #omg-ponies; I just want to add that this error also occur in variable assignment. In my case I used an insert; associated with that insert was a trigger. I mistakenly assign different number of fields to different number of variables. Below is my case details.
INSERT INTO tab1 (event, eventTypeID, fromDate, toDate, remarks)
-> SELECT event, eventTypeID,
-> fromDate, toDate, remarks FROM rrp group by trainingCode;
ERROR 1222 (21000): The used SELECT statements have a different number of columns
So you see I got this error by issuing an insert statement instead of union statement. My case difference were
I issued a bulk insert sql
i.e. insert into tab1 (field, ...) as select field, ... from tab2
tab2 had an on insert trigger; this trigger basically decline duplicates
It turns out that I had an error in the trigger. I fetch record based on new input data and assigned them in incorrect number of variables.
DELIMITER ##
DROP TRIGGER trgInsertTrigger ##
CREATE TRIGGER trgInsertTrigger
BEFORE INSERT ON training
FOR EACH ROW
BEGIN
SET #recs = 0;
SET #trgID = 0;
SET #trgDescID = 0;
SET #trgDesc = '';
SET #district = '';
SET #msg = '';
SELECT COUNT(*), t.trainingID, td.trgDescID, td.trgDescName, t.trgDistrictID
INTO #recs, #trgID, #trgDescID, #proj, #trgDesc, #district
from training as t
left join trainingDistrict as tdist on t.trainingID = tdist.trainingID
left join trgDesc as td on t.trgDescID = td.trgDescID
WHERE
t.trgDescID = NEW.trgDescID
AND t.venue = NEW.venue
AND t.fromDate = NEW.fromDate
AND t.toDate = NEW.toDate
AND t.gender = NEW.gender
AND t.totalParticipants = NEW.totalParticipants
AND t.districtIDs = NEW.districtIDs;
IF #recs > 0 THEN
SET #msg = CONCAT('Error: Duplicate Training: previous ID ', CAST(#trgID AS CHAR CHARACTER SET utf8) COLLATE utf8_bin);
SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = #msg;
END IF;
END ##
DELIMITER ;
As you can see i am fetching 5 fields but assigning them in 6 var. (My fault totally I forgot to delete the variable after editing.

Answer 5

You are using MySQL Union.
UNION is used to combine the result from multiple SELECT statements into a single result set.
The column names from the first SELECT statement are used as the column names for the results returned. Selected columns listed in corresponding positions of each SELECT statement should have the same data type. (For example, the first column selected by the first statement should have the same type as the first column selected by the other statements.)
Reference: MySQL Union
Your first select statement has 4 columns and second statement has 6 as you said wall_post has 6 column.
You should have same number of column and also in same order in both statement.
otherwise it shows error or wrong data.