數據庫複雜查詢

[b][size=x-large]1。內連接結合左連接[/size][/b]
[size=large]首先是數據庫表a和數據庫表b的內連接，然後是數據庫表a與數據庫表c的左連接。
on和where後面跟隨的都是條件[/size]

select * from
a inner join b on 條件 where ...
left join c on 條件 where ...

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2、列出一張表同一字段出現大於等於2次的列，sql怎麼表達
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select t.vcexpressinvoicecode,count(t.vcexpressinvoicecode) from tbexpressinvoice t
group by  t.vcexpressinvoicecode
having count(t.vcexpressinvoicecode)>2;