如何在sql查询中使用group？

Question

SELECT DISTINCT 
           t1.name as t1_name, 
           MAX(t1.unit) as t1_unit, 
           MAX(t1.id_producer_goods) AS hi_id_producer_goods, 
          t2.name as t2_name 
FROM Table1 t1 
    left join Table2 t2 on t1.id_web_site=t2.id_web_site 
WHERE t1.id='23'  
GROUP BY t1.name

当我运行查询时,我收到以下错误:

Column 'Table2.name' is invalid in the select list because it is not contained 
in either an aggregate function or the GROUP BY clause.

怎么写这个查询？

Answer 1

错误很明显,要么使用聚合函数,t2.name要么将其添加到GROUP BY,它取决于您要查找的所需结果:

SELECT 
  t1.name as t1_name, 
  t2.name as t2_name,
  MAX(t1.unit) as t1_unit, 
  MAX(t1.id_producer_goods) AS hi_id_producer_goods
FROM Table1 hi 
left join Table2 t2 on t1.id_web_site=t2.id_web_site 
WHERE t1.id='23'  
GROUP BY t1.name, t2.name;

这个错误是有道理的,因为它必须知道从t2.name每个组中选择哪个值t1.name？它应该选择max,min等,否则GROUP BY它.

此外,删除DISTINCT没有必要GROUP BY.