最新话题
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1.count 计算指定字段在查询结果中出现sele的个数 SELECT COUNT(employee_id),COUNT(salary),COUNT(salary12) from employees...0299 -
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1显示所有员工的姓名，部门号和部门名称 SELECT last_name,e.department_id,department_name from employees e LEFT JOIN dep...0241
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七、聚合函数 1.常见的聚合函数 1. AVG / SUM AVG 求平均数 SELECT AVG (salary) FROM employees; 以下两个是字符串， 它们在求平均数和求和时...0281
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SELECT last_name,e.department_id,department_name from employees e LEFT JOIN departments d on e.depar...0346
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SELECT last_name,e.department_id, department_name FROM employees e LEFT OUTER JOIN departments d ON ...0339
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1.avg/sum:只适用于数值类型的字段或变量 SELECT AVG(salary),SUM(salary) from employees; 字符串求和没有任何意义 SELECT AVG(last_...0320
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练习SELECT e.last_name,d.department_id,d.department_name FROM employees e,departments d WHERE e.depart...0246
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满外连接(mysql不支持使用FULL OUTER JOIN) SELECT employees_id,department_name FROM employees e FULL OUTER JOIN...1279
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SELECT employees_id,department_name FROM employees e 满外连接 SELECT EMPLOYEE_id,department_name FROM em...2255
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满外链接 MYSQL不支持FULL OUTER JOIN 做满外链接 SELECT employee_id,department_name FROM employees e FULL OUTER ...0265
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满外查询 错误写法(MySQL不支持FULL OUTER JOIN 做满外查询 ) SELECT employee_id,department_name FROM employees e FULL...0247
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select 122106; Mysql 不支持full outer join 做满外查询 select employee_id,department_name from employees e fu...0279