17 lines
459 B
SQL
17 lines
459 B
SQL
## 查询表有多少条记录
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SELECT COUNT(*) AS num FROM emp;
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## 查询年龄大于40人员数量
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SELECT COUNT(*) FROM emp WHERE age>40;
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# sum()：求和
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SELECT SUM(age) FROM emp
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# avg(): 计算平均数
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SELECT AVG(age) FROM emp
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## 把平均数值小数点后面位数
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SELECT AVG(age) AS avgnum FROM emp
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#cast转换类型
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SELECT CAST(AVG(age) AS DECIMAL(10,2)) AS avgnum FROM emp
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#最大值和最小值
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SELECT MAX(age) FROM emp;
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SELECT MIN(age) FROM emp;
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