sql中having 与group by详解

GROUP BY 实例
表 "Sales":
Company Amount
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IBM 5500
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SQL:
SELECT Company, SUM(Amount) from Sales
结果:
Company SUM(Amount)
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上面的代码是无效的，这是由于被返回的列没有进行部分合计。GROUP BY 子句能解决这个问题：
SELECT Company,SUM(Amount) from Sales
GROUP BY Company
结果:
Company SUM(Amount)
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HAVING...
把 HAVING 加入 SQL 的原因是，WHERE 无法应用于合计函数，而如果没有 HAVING，就无法测试结果条件。
HAVING 的语法:
SELECT column,SUM(column) from table
GROUP BY column
HAVING SUM(column) condition value
表 "Sales":
Company Amount
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IBM 5500
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SQL:
SELECT Company,SUM(Amount) from Sales
GROUP BY Company
HAVING SUM(Amount)>10000
结果：
Company SUM(Amount)
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