MySQL - #1054 - Unknown column 'childs' in 'on clause' - mysql

Question

I'm very new in comlex SQL queries. So, I'm trying to debug SQL statement generated by Magento:
SELECT `e`.*,
`cat_index`.`position` AS
`cat_index_position`,
price_index.price AS
`indexed_price`,
`price_index`.`price`,
`price_index`.`final_price`,
IF(`price_index`.`tier_price`, Least(`price_index`.`min_price`,
`price_index`.`tier_price`),
`price_index`.`min_price`) AS
`minimal_price`,
`price_index`.`min_price`,
`price_index`.`max_price`,
`price_index`.`tier_price`,
GROUP_CONCAT(CONVERT(catalog_product_relation.child_id, CHAR(8))) AS
`children`,
`sfoi`.`price` AS
`confprice`
FROM `catalog_product_entity` AS `e`
INNER JOIN `catalog_category_product_index` AS `cat_index`
ON cat_index.product_id = e.entity_id
AND cat_index.store_id = 1
AND cat_index.visibility IN( 2, 4 )
AND cat_index.category_id = '3'
INNER JOIN `catalog_product_index_price` AS `price_index`
ON price_index.entity_id = e.entity_id
AND price_index.website_id = '1'
AND price_index.customer_group_id = 0
INNER JOIN `catalog_product_index_eav` AS `attributeA`
ON attributeA.entity_id = e.entity_id
AND attributeA.attribute_id = '184'
AND attributeA.store_id = '1'
AND attributeA.value IN ( 50 )
INNER JOIN `catalog_product_index_eav` AS `attributeB`
ON attributeB.entity_id = e.entity_id
AND attributeB.attribute_id = '185'
AND attributeB.store_id = '1'
AND attributeB.value IN ( 95 )
LEFT JOIN `catalog_product_relation`
ON e.entity_id = catalog_product_relation.parent_id
LEFT JOIN `catalog_product_flat_1` AS `sfoi`
ON sfoi.entity_id = `children`
GROUP BY `e`.`entity_id`
ORDER BY `confprice` DESC
LIMIT 9
Everything work fine until:
LEFT JOIN `catalog_product_flat_1` AS `sfoi`
ON sfoi.entity_id = `children`
I get following error:
#1054 - Unknown column 'children' in 'on clause'
I've seen smilar posts, but I can't seem to figure it out by myself. Please, help me.
EDIT:
PHP code that generates this query:
$this->_collection->getSelect()->
joinLeft(
'catalog_product_relation',
'e.entity_id = catalog_product_relation.parent_id',
'GROUP_CONCAT(CONVERT(catalog_product_relation.child_id, CHAR(8))) as children'
);
$this->_collection->getSelect()->joinLeft('catalog_product_flat_1 AS sfoi',
'sfoi.entity_id = children',
'sfoi.price AS confprice'
)->order('confprice desc');
Actually, I'm trying to join two tables (catalog_product_relation and catalog_product_flat_1). But I can't get access to the "children" column after joining first table.

Answer 1

Add the corresponding column to children table in the ON condition.
ON sfoi.entity_id = catalog_product_relation.child_id