Mysql - associative table - Unknown column in on clause - php

Question

The following query always returns #1054 - Unknown column 'T_RELATIF_SESS.REL_COM_ID' in 'on clause'
SELECT
`T_FORMATIONS`.`FOR_ID`,
`T_FORMATIONS`.`FOR_TITRE`,
`T_FORMATIONS`.`FOR_NIVEAU`,
`T_FORMATIONS`.`FOR_MAX_PART`,
`T_RELATIF_SESS`.`REL_COM_ID`,
`T_RELATIF_SESS`.`REL_SES_ID`,
`T_SESSIONS`.`SES_ID`,
`T_SESSIONS`.`SES_TITRE`,
`T_SESSIONS`.`SES_TYPE`,
`T_SESSIONS`.`SES_ADRESSE`,
`T_SESSIONS`.`SES_NPA`,
`T_SESSIONS`.`SES_LIEU`,
`T_SESSIONS`.`SES_PRIX_SPECIAL`,
`T_SESSIONS`.`SES_VAL_PRIX_SPECIAL`,
`T_SESSIONS`.`SES_PRIX_SPEC_EXP`,
`T_SESSIONS`.`SES_SUPP_COURS_INCL`,
`T_SESSIONS`.`SES_SUPP_COURS_ADD`,
`T_SESSIONS`.`SES_PRIX_SUPP_COURS_ADD`,
`T_SESSIONS`.`SES_HORAIRE_SPECIAL`,
`T_SESSIONS`.`SES_REMARQUES`,
`T_SESSIONS`.`SES_REC_ID`,
`T_COURS`.`COU_ID`,
`T_COURS`.`COU_DATE`,
(SELECT `COU_DATE` FROM `T_COURS` WHERE `T_COURS`.`COU_SES_ID` = `T_SESSIONS`.`SES_ID` ORDER BY `COU_DATE` ASC LIMIT 1) AS `PREMIERCOURS`,
(SELECT `COU_DATE` FROM `T_COURS` WHERE `T_COURS`.`COU_SES_ID` = `T_SESSIONS`.`SES_ID` ORDER BY `COU_DATE` DESC LIMIT 1) AS `DERNIERCOURS`
FROM `T_COURS`
INNER JOIN `T_COMMANDES` ON `T_RELATIF_SESS`.`REL_COM_ID` = `T_COMMANDES`.`COM_ID`
INNER JOIN `T_RELATIF_SESS` ON `T_SESSIONS`.`SES_ID` = `T_RELATIF_SESS`.`REL_SES_ID`
INNER JOIN `T_SESSIONS` ON `T_COURS`.`COU_SES_ID` = `T_SESSIONS`.`SES_ID`
INNER JOIN `T_FORMATIONS` ON `T_SESSIONS`.`SES_FOR_ID` = `T_FORMATIONS`.`FOR_ID`
WHERE `T_COMMANDES`.`COM_ID`=19
This query worked fine before I add
INNER JOIN `T_COMMANDES` ON `T_RELATIF_SESS`.`REL_COM_ID` = `T_COMMANDES`.`COM_ID`
INNER JOIN `T_RELATIF_SESS` ON `T_SESSIONS`.`SES_ID` = `T_RELATIF_SESS`.`REL_SES_ID`
And
WHERE `T_COMMANDES`.`COM_ID`=19
T_RELATIF_SESS is juste an associative table between the tables called "T_SESSIONS" and "T_COMMANDES".
I've tried to rewrite the query many times but I still get this error and I really don't understand why. Every field exists in my database.
I know it may be simple but it really gives me headache. Can someone can give me a hand or just explain to me what I do wrong? It would be much apprecietaded!
Thank you very much!

Answer 1

So from your description you try to run the script without
INNER JOIN `T_COMMANDES` ON `T_RELATIF_SESS`.`REL_COM_ID` = `T_COMMANDES`.`COM_ID`
INNER JOIN `T_RELATIF_SESS` ON `T_SESSIONS`.`SES_ID` = `T_RELATIF_SESS`.`REL_SES_ID`
and it is working, but not with that script? Try to make it in order, since on your first inner join, you are trying to join the table (T_COMMANDES) with the table that you will join next (T_RELATIF_SESS).
So try:
INNER JOIN `T_SESSIONS` ON `T_COURS`.`COU_SES_ID` = `T_SESSIONS`.`SES_ID`
INNER JOIN `T_FORMATIONS` ON `T_SESSIONS`.`SES_FOR_ID` = `T_FORMATIONS`.`FOR_ID`
INNER JOIN `T_RELATIF_SESS` ON `T_SESSIONS`.`SES_ID` = `T_RELATIF_SESS`.`REL_SES_ID`
INNER JOIN `T_COMMANDES` ON `T_RELATIF_SESS`.`REL_COM_ID` = `T_COMMANDES`.`COM_ID`

Answer 2

your order of table are messed up after you add your join, since you are using INNER JOIN, you can declare the table anywhere you like as long as the fields are visible on the joins. It will still yield the same result.
To solve the problem, put those new join on the lower part of your joins:
FROM T_COURS
INNER JOIN T_SESSIONS
ON T_COURS.COU_SES_ID = T_SESSIONS.SES_ID
INNER JOIN T_FORMATIONS
ON T_SESSIONS.SES_FOR_ID = T_FORMATIONS.FOR_ID
INNER JOIN T_RELATIF_SESS
ON T_SESSIONS.SES_ID = T_RELATIF_SESS.REL_SES_ID
INNER JOIN T_COMMANDES
ON T_RELATIF_SESS.REL_COM_ID = T_COMMANDES.COM_ID
The reason why an error message: Unknown column 'T_RELATIF_SESS.REL_COM_ID' in 'on clause' was thrown is because when joining T_COURS with T_COMMANDES, column T_RELATIF_SESS.REL_COM_ID isn't visible yet since you have declared table T_RELATIF_SESS on the lower part of the join.

Answer 3

You try to access T_RELATIF_SESS before you have joined the table. You must join T_COMMANDES after T_RELATIF_SESS and T_RELATIF_SESS after T_SESSIONS
SELECT
`T_FORMATIONS`.`FOR_ID`,
...
FROM `T_COURS`
INNER JOIN `T_SESSIONS` ON `T_COURS`.`COU_SES_ID` = `T_SESSIONS`.`SES_ID`
INNER JOIN `T_FORMATIONS` ON `T_SESSIONS`.`SES_FOR_ID` = `T_FORMATIONS`.`FOR_ID`
INNER JOIN `T_RELATIF_SESS` ON `T_SESSIONS`.`SES_ID` = `T_RELATIF_SESS`.`REL_SES_ID`
INNER JOIN `T_COMMANDES` ON `T_RELATIF_SESS`.`REL_COM_ID` = `T_COMMANDES`.`COM_ID`
WHERE `T_COMMANDES`.`COM_ID`=19