67 lines
1.8 KiB
SQL
67 lines
1.8 KiB
SQL
#去重操作,不重复显示
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SELECT DISTINCT ename FROM emp
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#查询年龄大于20
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SELECT * FROM emp WHERE age>20
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#模糊查询，查询所有名字开头为J的信息
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#%代表通配符，匹配任意内容
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SELECT * FROM emp WHERE ename LIKE 'j%'
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#模糊查询，查询所有名字结尾为k的信息
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SELECT * FROM emp WHERE ename LIKE '%k'
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#模糊查询，查询所有名字中包含a的信息
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SELECT * FROM emp WHERE ename LIKE '%a%'
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#模糊查询，查询所有名字开头为J，后面包含三个字母的信息
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#_代表站位符，匹配任意内容
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SELECT * FROM emp WHERE ename LIKE 'j___'
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#排序操作
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##查询emp表所有记录，根据eid进行排序ASC升序,DESC降序
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SELECT * FROM emp ORDER BY eid DESC
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#查询区间范围的值
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#查询emp表年龄30-50范围
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SELECT * FROM emp WHERE age>=30 AND age<=50
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SELECT * FROM emp WHERE age BETWEEN 30 AND 50
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#查询emp表年龄是20 40 60
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SELECT * FROM emp WHERE age IN(20,40,60)
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#分页查询
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#关键字limit,只能用在mysql中，不是标准sql
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#limit后面两个参数，第一个参数 查询数据开始位置；第二个参数 每页显示多少条记录
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SELECT * FROM emp LIMIT 0,3
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SELECT * FROM emp LIMIT 3,3
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#分组查询GROUP BY
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#查询每个edid有多少个人
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SELECT COUNT(*) AS num,edid FROM emp GROUP BY edid
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#GROUP BY 加上having操作
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##统计每个部门的最高工资#一对多关系
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#编写emp和salary内连接查询
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##得到最高工资max
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##部门分组group by
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SELECT MAX(salarystid) ,emp.edid
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FROM emp,salary
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WHERE emp.`stid`=salary.`stid`
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GROUP BY emp.`edid`
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# 获取最高工资大于5000的部门,having后可以加函数where后不能
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#在分组之上做筛选
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SELECT MAX(salarystand),emp.edid
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FROM emp,salary
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WHERE emp.stid=salary.stid
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GROUP BY emp.edid
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HAVING MAX(salarystand)>5000
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