MySQL many to many relationship, grouping and splicing to query multiple data to one data

• GROUP_CONCAT(str)： Grouping string splicing , And Use together in groups

Case study ： Query enterprise information and enterprise classification information , Among them, the relationship between enterprise classification information and enterprise is many to many , Query according to the common joint table , We will find that one piece of enterprise information corresponds to multiple enterprise classifications , Multiple records will appear . If you want to classify different enterprises of the same enterprise into one record , You can consider using it GROUP_CONCAT, This function will splice multiple pieces of data onto one piece of data （ By default , Division ）

Direct linked table query , You will see that the enterprise classification associated with an enterprise is multiple data

select t_enterprise.*,
				dic_enterprise_category.name as enterpriseCategoryNames,
        dic_operation_status.name as operationStatusName,
				dic_region.name as regionName
        from t_enterprise
				left join ref_enterprise_category
        on t_enterprise.id = ref_enterprise_category.enterprise_id 
				left join dic_enterprise_category
        on dic_enterprise_category.id = ref_enterprise_category.category_id
        left join dic_operation_status
        on t_enterprise.operate_status_id = dic_operation_status.id
				left join dic_region
        on t_enterprise.region_id = dic_region.id

Use GROUP_CONCAT

select 
t_enterprise.*,
GROUP_CONCAT(DISTINCT  dic_enterprise_category.name) as enterpriseCategoryNames,
dic_operation_status.name as operationStatusName,
dic_region.name as regionName
from t_enterprise
	left join ref_enterprise_category
        on t_enterprise.id = ref_enterprise_category.enterprise_id 
	left join dic_enterprise_category
        on dic_enterprise_category.id = ref_enterprise_category.category_id
    left join dic_operation_status
        on t_enterprise.operate_status_id = dic_operation_status.id
	left join dic_region
        on t_enterprise.region_id = dic_region.id
GROUP BY id				
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