① union（去重，排序）取并集并且去重，按照第一个查询语句的第一个字段升序排序
②union all（不去重，不排序）并集，相当于两个查询语句结果堆集，无序，不去重
③intersect ： 取交集
④minus：第二个查询结果的补集，这个补集是第一个查询结果的子集
除了union all 不排序，其他都排序去重
1.union
SQL> select employee_id,job_id
2 from employees
3 union
4 select employee_id,job_id
5 from job_history;
EMPLOYEE_ID JOB_ID
----------- ----------
100 AD_PRES
101 AC_ACCOUNT
101 AC_MGR
101 AD_VP
102 AD_VP
102 IT_PROG
103 IT_PROG
104 IT_PROG
105 IT_PROG
106 IT_PROG
107 IT_PROG
EMPLOYEE_ID JOB_ID
----------- ----------
108 FI_MGR
109 FI_ACCOUNT
110 FI_ACCOUNT
111 FI_ACCOUNT
112 FI_ACCOUNT
113 FI_ACCOUNT
114 PU_MAN
114 ST_CLERK
115 PU_CLERK
116 PU_CLERK
117 PU_CLERK
EMPLOYEE_ID JOB_ID
----------- ----------
118 PU_CLERK
119 PU_CLERK
120 ST_MAN
121 ST_MAN
122 ST_CLERK
122 ST_MAN
123 ST_MAN
124 ST_MAN
125 ST_CLERK
126 ST_CLERK
127 ST_CLERK
EMPLOYEE_ID JOB_ID
----------- ----------
128 ST_CLERK
129 ST_CLERK
130 ST_CLERK
131 ST_CLERK
132 ST_CLERK
133 ST_CLERK
134 ST_CLERK
135 ST_CLERK
136 ST_CLERK
137 ST_CLERK
138 ST_CLERK
EMPLOYEE_ID JOB_ID
----------- ----------
139 ST_CLERK
140 ST_CLERK
141 ST_CLERK
142 ST_CLERK
143 ST_CLERK
144 ST_CLERK
145 SA_MAN
146 SA_MAN
147 SA_MAN
148 SA_MAN
149 SA_MAN
EMPLOYEE_ID JOB_ID
----------- ----------
150 SA_REP
151 SA_REP
152 SA_REP
153 SA_REP
154 SA_REP
155 SA_REP
156 SA_REP
157 SA_REP
158 SA_REP
159 SA_REP
160 SA_REP
EMPLOYEE_ID JOB_ID
----------- ----------
161 SA_REP
162 SA_REP
163 SA_REP
164 SA_REP
165 SA_REP
166 SA_REP
167 SA_REP
168 SA_REP
169 SA_REP
170 SA_REP
171 SA_REP
EMPLOYEE_ID JOB_ID
----------- ----------
172 SA_REP
173 SA_REP
174 SA_REP
175 SA_REP
176 SA_MAN
176 SA_REP
177 SA_REP
178 SA_REP
179 SA_REP
180 SH_CLERK
181 SH_CLERK
EMPLOYEE_ID JOB_ID
----------- ----------
182 SH_CLERK
183 SH_CLERK
184 SH_CLERK
185 SH_CLERK
186 SH_CLERK
187 SH_CLERK
188 SH_CLERK
189 SH_CLERK
190 SH_CLERK
191 SH_CLERK
192 SH_CLERK
EMPLOYEE_ID JOB_ID
----------- ----------
193 SH_CLERK
194 SH_CLERK
195 SH_CLERK
196 SH_CLERK
197 SH_CLERK
198 SH_CLERK
199 SH_CLERK
200 AC_ACCOUNT
200 AD_ASST
201 MK_MAN
201 MK_REP
EMPLOYEE_ID JOB_ID
----------- ----------
202 MK_REP
203 HR_REP
204 PR_REP
205 AC_MGR
206 AC_ACCOUNT
115 rows selected.
②union all
SQL> select employee_id,job_id,department_id
2 from employees
3 union all
4 select employee_id,job_id,department_id
5 from job_history
6 order by employee_id;
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
100 AD_PRES 90
101 AD_VP 90
101 AC_ACCOUNT 110
101 AC_MGR 110
102 AD_VP 90
102 IT_PROG 60
103 IT_PROG 60
104 IT_PROG 60
105 IT_PROG 60
106 IT_PROG 60
107 IT_PROG 60
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
108 FI_MGR 100
109 FI_ACCOUNT 100
110 FI_ACCOUNT 100
111 FI_ACCOUNT 100
112 FI_ACCOUNT 100
113 FI_ACCOUNT 100
114 PU_MAN 30
114 ST_CLERK 50
115 PU_CLERK 30
116 PU_CLERK 30
117 PU_CLERK 30
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
118 PU_CLERK 30
119 PU_CLERK 30
120 ST_MAN 50
121 ST_MAN 50
122 ST_MAN 50
122 ST_CLERK 50
123 ST_MAN 50
124 ST_MAN 50
125 ST_CLERK 50
126 ST_CLERK 50
127 ST_CLERK 50
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
128 ST_CLERK 50
129 ST_CLERK 50
130 ST_CLERK 50
131 ST_CLERK 50
132 ST_CLERK 50
133 ST_CLERK 50
134 ST_CLERK 50
135 ST_CLERK 50
136 ST_CLERK 50
137 ST_CLERK 50
138 ST_CLERK 50
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
139 ST_CLERK 50
140 ST_CLERK 50
141 ST_CLERK 50
142 ST_CLERK 50
143 ST_CLERK 50
144 ST_CLERK 50
145 SA_MAN 80
146 SA_MAN 80
147 SA_MAN 80
148 SA_MAN 80
149 SA_MAN 80
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
150 SA_REP 80
151 SA_REP 80
152 SA_REP 80
153 SA_REP 80
154 SA_REP 80
155 SA_REP 80
156 SA_REP 80
157 SA_REP 80
158 SA_REP 80
159 SA_REP 80
160 SA_REP 80
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
161 SA_REP 80
162 SA_REP 80
163 SA_REP 80
164 SA_REP 80
165 SA_REP 80
166 SA_REP 80
167 SA_REP 80
168 SA_REP 80
169 SA_REP 80
170 SA_REP 80
171 SA_REP 80
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
172 SA_REP 80
173 SA_REP 80
174 SA_REP 80
175 SA_REP 80
176 SA_REP 80
176 SA_REP 80
176 SA_MAN 80
177 SA_REP 80
178 SA_REP
179 SA_REP 80
180 SH_CLERK 50
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
181 SH_CLERK 50
182 SH_CLERK 50
183 SH_CLERK 50
184 SH_CLERK 50
185 SH_CLERK 50
186 SH_CLERK 50
187 SH_CLERK 50
188 SH_CLERK 50
189 SH_CLERK 50
190 SH_CLERK 50
191 SH_CLERK 50
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
192 SH_CLERK 50
193 SH_CLERK 50
194 SH_CLERK 50
195 SH_CLERK 50
196 SH_CLERK 50
197 SH_CLERK 50
198 SH_CLERK 50
199 SH_CLERK 50
200 AD_ASST 10
200 AC_ACCOUNT 90
200 AD_ASST 90
EMPLOYEE_ID JOB_ID DEPARTMENT_ID
----------- ---------- -------------
201 MK_MAN 20
201 MK_REP 20
202 MK_REP 20
203 HR_REP 40
204 PR_REP 70
205 AC_MGR 110
206 AC_ACCOUNT 110
117 rows selected.
③intersect
SQL> select employee_id,job_id
2 from employees
3 intersect
4 select employee_id,job_id
5 from job_history;
EMPLOYEE_ID JOB_ID
----------- ----------
176 SA_REP
200 AD_ASST
④minus
SQL> select employee_id
2 from employees
3 minus
4 select employee_id
5 from job_history;
EMPLOYEE_ID
-----------
100
103
104
105
106
107
108
109
110
111
112
EMPLOYEE_ID
-----------
113
115
116
117
118
119
120
121
123
124
125
EMPLOYEE_ID
-----------
126
127
128
129
130
131
132
133
134
135
136
EMPLOYEE_ID
-----------
137
138
139
140
141
142
143
144
145
146
147
EMPLOYEE_ID
-----------
148
149
150
151
152
153
154
155
156
157
158
EMPLOYEE_ID
-----------
159
160
161
162
163
164
165
166
167
168
169
EMPLOYEE_ID
-----------
170
171
172
173
174
175
177
178
179
180
181
EMPLOYEE_ID
-----------
182
183
184
185
186
187
188
189
190
191
192
EMPLOYEE_ID
-----------
193
194
195
196
197
198
199
202
203
204
205
EMPLOYEE_ID
-----------
206
100 rows selected.