MYSQL使用UNION选择查询以合并来自共享相同密钥的三个表的数据

Question

我的查询是这样构建的，但我没有得到预期的结果。我有像

这样的表格

1. company_group- group_company_id，group_company_name
2. store - store_id，store_name
3. sales_report- sales_id，group_company_id，store_id，sales_4，vat_4
4. warehouse_sales - warehouse_sales_id，warehouse_sales_id（FK-group_company_id），store_name（FK-store_id），日期，sales_four_percent
5. Stock_recpt- Stock_recpt_id，group_company_id，receipt_date，input_vat_4

这个查询得到的结果如

company_group store_name月sales_4 vat_4 input_vat

SELECT firm, store_name, MONTH, sales_4, vat_4, input_vat_4
FROM (select `company_group`.`group_company_name`as firm,`store`.`store_name`as store_name, MONTHNAME( receipt_date ) AS MONTH,0 AS sales_4, 0 as vat_4,sum(`input_vat_4_percent`)as input_vat_4 from
company_group,store, Stock_recpt
WHERE `company_group`.`group_company_id` = `Stock_recpt`.`group_company_id`and `store`.`store_id` = `Stock_recpt`.`store_id` and  `Stock_recpt`.`purchase_type` = 'purchase_4_percent' 
UNION

SELECT `company_group`.`group_company_name`as firm , `store`.`store_name`as store_name , MONTHNAME(date) AS MONTH , sum( `warehouse_sales`.`sales_four_percent`)as sales_4, sum( `warehouse_sales`.`vat_four_percent` ) AS vat_4, 0 as input_vat_4 

from company_group,store, warehouse_sales
WHERE `company_group`.`group_company_id` = `warehouse_sales`.`firm_name`and `store`.`store_id` = `warehouse_sales`.`store_name`  

UNION

SELECT `company_group`.`group_company_name` as firm, `store`.`store_name`as store_name,MONTHNAME( sale_date ) AS MONTH, sum( `sales_report`.`sales_four_percent`)as sales_4, sum( `sales_report`.`vat_four_percent` ) AS vat_4,0 as input_vat_4

FROM company_group,store, sales_report
WHERE `company_group`.`group_company_id` = `sales_report`.`group_company_id`and `store`.`store_id` = `sales_report`.`store_id`)a
GROUP BY firm , store_name,`MONTH`