Insert where in join, code confused - mysql

Question

This code returns me the most used words in a column in TEXT format called description and is on the table 'messages`.
However I can not stick this in the WHERE code:
messages.tag = 'HELLO'
I need it to do what it already does, but with this WHERE I tried this code and gave not sure:
SELECT message, count(message) as count
FROM (
SELECT
messages.id,
SUBSTRING_INDEX(SUBSTRING_INDEX(messages.message, ' ', count.n), ' ', -1) as message
FROM
(select (h*100+t*10+u+1) n from
(select 0 h union select 1 union select 2 union select 3 union select 4 union
select 5 union select 6 union select 7 union select 8 union select 9) A,
(select 0 t union select 1 union select 2 union select 3 union select 4 union
select 5 union select 6 union select 7 union select 8 union select 9) B,
(select 0 u union select 1 union select 2 union select 3 union select 4 union
select 5 union select 6 union select 7 union select 8 union select 9) C
) as count
INNER JOIN messages
ON CHAR_LENGTH(messages.message)-CHAR_LENGTH(REPLACE(messages.message, ' ',''))>=count.n-1
ORDER BY id, n
) x
WHERE LENGTH(message) >= 5
AND messages.tag = 'HELLO'
GROUP BY message
ORDER BY count DESC
LIMIT 10

Answer 1

You have to move that where clause into the subquery. The messages alias is not known in the outer query:
FROM (SELECT messages.id,
SUBSTRING_INDEX(SUBSTRING_INDEX(messages.message, ' ', count.n), ' ', -1) as message
FROM (select (h*100+t*10+u+1) n
from (select 0 h union select 1 union select 2 union select 3 union select 4 union
select 5 union select 6 union select 7 union select 8 union select 9) A,
(select 0 t union select 1 union select 2 union select 3 union select 4 union
select 5 union select 6 union select 7 union select 8 union select 9) B,
(select 0 u union select 1 union select 2 union select 3 union select 4 union
select 5 union select 6 union select 7 union select 8 union select 9) C
) count INNER JOIN
messages
ON CHAR_LENGTH(messages.message)-CHAR_LENGTH(REPLACE(messages.message, ' ','')) >= count.n-1
WHERE messages.tag = 'HELLO'
ORDER BY id, n
) x
The other condition stays in the outer query.

Answer 2

Try this,
I think messages.tag should be like, not equal to 'HELLO'
SELECT message, count(message) as count
FROM (
SELECT
messages.id,
SUBSTRING_INDEX(SUBSTRING_INDEX(messages.message, ' ', count.n), ' ', -1) as message
FROM
(
select (h*100+t*10+u+1) n
from
(
select 0 h union select 1 union select 2 union select 3 union select 4
union
select 5 union select 6 union select 7 union select 8 union select 9) A,
(select 0 t union select 1 union select 2 union select 3 union select 4
union
select 5 union select 6 union select 7 union select 8 union select 9) B,
(select 0 u union select 1 union select 2 union select 3 union select 4
union
select 5 union select 6 union select 7 union select 8 union select 9) C
) count
INNER JOIN messages
ON CHAR_LENGTH(messages.message)-CHAR_LENGTH(REPLACE(messages.message, ' ',''))>=count.n-1
WHERE messages.tag like '%HELLO%'
ORDER BY id, n
) x
WHERE LENGTH(message) >= 5
GROUP BY message
ORDER BY count DESC
LIMIT 10