lyt经典版MySQL基础——进阶6：连接查询-sql99语法-内连接、外连接、交叉连接

  1 #二、sql99语法
  2 
 21 
 22 #（一）内连接
 23 
 42 
 43 #1.等值连接
 44 #案例1：查询员工名、部门名
 45 SELECT last_name,department_name 
 46 FROM employees e
 47 INNER JOIN departments d
 48 ON e.department_id=d.department_id;
 49 #案例2：查询名字中包含e的员工名和工种名（添加筛选）
 50 SELECT last_name,job_title
 51 FROM employees e
 52 INNER JOIN jobs j
 53 ON e.job_id=j.job_id
 54 WHERE last_name LIKE ‘%e%‘;
 55 #案例3：查询部门个数>3的城市名和部门个数（分组+筛选）
 56 #(1)查询每个城市的部门个数
 57 #(2)在(1)结果上筛选满足条件的
 58 SELECT city,COUNT(*) ‘部门个数‘
 59 FROM locations l
 60 INNER JOIN departments d
 61 ON l.location_id=d.location_id
 62 GROUP BY city
 63 HAVING 部门个数>3;
 64 #案例4：查询哪个部门的部门员工个数>3的部门名和员工个数，
 65 #并按个数降序（添加排序）
 66 SELECT department_name,COUNT(*) ‘员工个数‘
 67 FROM departments d
 68 INNER JOIN employees e
 69 ON d.department_id=e.department_id
 70 GROUP BY e.department_id
 71 HAVING 员工个数>3
 72 ORDER BY 员工个数 DESC;
 73 #案例5：查询员工名、部门名、工种名，并按部门名降序
 74 SELECT last_name,department_name,job_title
 75 FROM employees e
 76 INNER JOIN departments d ON e.department_id=d.department_id
 77 INNER JOIN jobs j ON e.job_id=j.job_id
 78 ORDER BY job_title DESC;
 79 
 80 #2.非等值连接
 81 #查询员工的工资级别
 82 SELECT salary,grade_level
 83 FROM employees
 84 JOIN job_grades
 85 ON salary BETWEEN lowest_sal AND highest_sal;
 86 #查询工资级别的个数>2的个数，并且按工资级别降序
 87 SELECT grade_level,COUNT(*) ‘个数‘
 88 FROM employees
 89 JOIN job_grades
 90 ON salary BETWEEN lowest_sal AND highest_sal
 91 GROUP BY grade_level
 92 HAVING 个数>2
 93 ORDER BY grade_level DESC;
 94 
 95 #3.自连接
 96 #查询员工的名字、上级的名字
 97 SELECT e.last_name,m.last_name
 98 FROM employees e
 99 JOIN employees m ON e.manager_id=m.employee_id;
100 #查询姓名中包含字符k的员工的名字、上级的名字
101 SELECT e.last_name,m.last_name
102 FROM employees e
103 JOIN employees m ON e.manager_id=m.employee_id
104 WHERE e.last_name LIKE ‘%k%‘;
105 
106 #（二）外连接
107 
120 #引入：查询男朋友不在男神表的女神名
121 SELECT * FROM beauty;
122 SELECT * FROM boys;
123 #左外连接
124 SELECT b.name,bo.*
125 FROM beauty b
126 LEFT OUTER JOIN boys bo
127 ON b.boyfriend_id=bo.id
128 WHERE bo.id IS NULL;
129 #右外连接
130 SELECT b.name,bo.*
131 FROM boys bo
132 RIGHT OUTER JOIN beauty b
133 ON b.boyfriend_id=bo.id
134 WHERE bo.id IS NULL;
135 
136 #案例1：查询哪个部门没有员工
137 #左外
138 SELECT d.*,e.employee_id
139 FROM departments d
140 LEFT OUTER JOIN employees e
141 ON d.department_id=e.department_id
142 WHERE employee_id IS NULL;
143 #右外
144 SELECT d.*,e.employee_id
145 FROM employees e
146 RIGHT OUTER JOIN departments d
147 ON d.department_id=e.department_id
148 WHERE employee_id IS NULL;
149 
150 #全外
151 USE girls;
152 SELECT b.*,bo.*
153 FROM bauty b
154 FULL OUTER JOIN boys bo
155 ON b.boyfriend_id=bo.id;
156 
157 #交叉连接
158 SELECT b.*,bo.*
159 FROM beauty b
160 CROSS JOIN boys bo;
161 
162 #sql92 和 sql99 PK
163 

lyt经典版MySQL基础——进阶6：连接查询-sql99语法-内连接、外连接、交叉连接

原文地址：https://www.cnblogs.com/yanwuliu/p/13373333.html