Objectives
After completing this lesson,you should be able to do the following:
- Write SELECT statements to access data from more than one table using equijoins and nonequijoins.
- Join a table to itself by using a self-join
- View data that generally does not meet a join condtions by using outer joins
- Generate a Cartesian product of all rows from two or more tables.
Lesson Agenda
Types of JOINS and its syntax
- Nature join:
- -USING clause
- -ON clause
- Self-join
- Nonequijoins
- OUTER join
- -LEFT OUTER join
- -RIGHT OUTER join
- -FULL OUTER join
- Cartesian product
- -Cross join
Obtaining Data from Multiple Tables
equijoin:两张表基于某个值相等,而连接起来.
Types of Joins
Joins that are complicant with the SQL:1999 standard include the following:
- Natural joins:
- -NATURAL JOIN clause
- -USING clause
- -ON clause
- Outer joins:
- -LEFT OUTER JOIN
- -RIGHT OUTER JOIN
- -FULL OUTER JOIN
- Cross joins
Joining Tables Using SQL:1999 Syntax
Use a join to query data from more than one table:
View Code
SELECT table1.column,table2.column FROM table1 [NATURAL JOIN table2] | [JOIN table2 USING (column_name)] | [JOIN table2 ON (table1.column_name = table2.column_name)] | [LEFT|RIGHT|OUTER JOIN table2 ON (table1.column_name = table2.column_name)] | [CROSS JOIN table2];
Joining Tables Using Oracle Syntax
- Use a join to query data from more than one table:
SELECT table1.column_name,table2.column_name FROM table1,table2 WHERE table1.column1 = table2.column2
- Write the join condition in the WHERE clause
- Prefix the column name with the table name when the same column name appears in more than one table.
INNER JOIN
SQL> SELECT e.employee_id,e.last_name,d.department_id,d.department_name FROM employees e,departments d WHERE e.department_id = d.department_id; EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 200 Whalen 10 Administration 201 Hartstein 20 Marketing 202 Fay 20 Marketing 114 Raphaely 30 Purchasing 119 Colmenares 30 Purchasing 115 Khoo 30 Purchasing 116 Baida 30 Purchasing 117 Tobias 30 Purchasing 118 Himuro 30 Purchasing 203 Mavris 40 Human Resources 198 OConnell 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 199 Grant 50 Shipping 120 Weiss 50 Shipping 121 Fripp 50 Shipping 122 Kaufling 50 Shipping 123 Vollman 50 Shipping 124 Mourgos 50 Shipping 125 Nayer 50 Shipping 126 Mikkilineni 50 Shipping 127 Landry 50 Shipping 128 Markle 50 Shipping 129 Bissot 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 130 Atkinson 50 Shipping 131 Marlow 50 Shipping 132 Olson 50 Shipping 133 Mallin 50 Shipping 134 Rogers 50 Shipping 135 Gee 50 Shipping 136 Philtanker 50 Shipping 137 Ladwig 50 Shipping 138 Stiles 50 Shipping 139 Seo 50 Shipping 140 Patel 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 141 Rajs 50 Shipping 142 Davies 50 Shipping 143 Matos 50 Shipping 144 Vargas 50 Shipping 180 Taylor 50 Shipping 181 Fleaur 50 Shipping 182 Sullivan 50 Shipping 183 Geoni 50 Shipping 184 Sarchand 50 Shipping 185 Bull 50 Shipping 186 Dellinger 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 187 Cabrio 50 Shipping 188 Chung 50 Shipping 189 Dilly 50 Shipping 190 Gates 50 Shipping 191 Perkins 50 Shipping 192 Bell 50 Shipping 193 Everett 50 Shipping 194 McCain 50 Shipping 195 Jones 50 Shipping 196 Walsh 50 Shipping 197 Feeney 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 104 Ernst 60 IT 103 Hunold 60 IT 107 Lorentz 60 IT 106 Pataballa 60 IT 105 Austin 60 IT 204 Baer 70 Public Relation s 176 Taylor 80 Sales 177 Livingston 80 Sales 179 Johnson 80 Sales EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 175 Hutton 80 Sales 174 Abel 80 Sales 173 Kumar 80 Sales 172 Bates 80 Sales 171 Smith 80 Sales 170 Fox 80 Sales 169 Bloom 80 Sales 168 Ozer 80 Sales 145 Russell 80 Sales 146 Partners 80 Sales 147 Errazuriz 80 Sales EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 148 Cambrault 80 Sales 149 Zlotkey 80 Sales 150 Tucker 80 Sales 151 Bernstein 80 Sales 152 Hall 80 Sales 153 Olsen 80 Sales 154 Cambrault 80 Sales 155 Tuvault 80 Sales 156 King 80 Sales 157 Sully 80 Sales 158 McEwen 80 Sales EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 159 Smith 80 Sales 160 Doran 80 Sales 161 Sewall 80 Sales 162 Vishney 80 Sales 163 Greene 80 Sales 164 Marvins 80 Sales 165 Lee 80 Sales 166 Ande 80 Sales 167 Banda 80 Sales 101 Kochhar 90 Executive 100 King 90 Executive EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 102 De Haan 90 Executive 110 Chen 100 Finance 108 Greenberg 100 Finance 111 Sciarra 100 Finance 112 Urman 100 Finance 113 Popp 100 Finance 109 Faviet 100 Finance 206 Gietz 110 Accounting 205 Higgins 110 Accounting 106 rows selected.
Qualifying Ambiguous Column Names
- Use table prefixes to qualify column names that are in multiple tables.
- Use table prefixes to improve performance
- Instead of full table name prefixes,use table aliases.
- Table alias gives a table a short name:
- -Keeps SQL code smaller,uses less memory
- Use column aliases to distinguish columns that have identical names,but reside in different tables.
正常别名使用
SQL> SELECT e.employee_id,e.last_name,d.department_id,d.department_name FROM employees e,departments d WHERE e.department_id = d.department_id; EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 200 Whalen 10 Administration 201 Hartstein 20 Marketing 202 Fay 20 Marketing 114 Raphaely 30 Purchasing 119 Colmenares 30 Purchasing 115 Khoo 30 Purchasing 116 Baida 30 Purchasing 117 Tobias 30 Purchasing 118 Himuro 30 Purchasing 203 Mavris 40 Human Resources 198 OConnell 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 199 Grant 50 Shipping 120 Weiss 50 Shipping 121 Fripp 50 Shipping 122 Kaufling 50 Shipping 123 Vollman 50 Shipping 124 Mourgos 50 Shipping 125 Nayer 50 Shipping 126 Mikkilineni 50 Shipping 127 Landry 50 Shipping 128 Markle 50 Shipping 129 Bissot 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 130 Atkinson 50 Shipping 131 Marlow 50 Shipping 132 Olson 50 Shipping 133 Mallin 50 Shipping 134 Rogers 50 Shipping 135 Gee 50 Shipping 136 Philtanker 50 Shipping 137 Ladwig 50 Shipping 138 Stiles 50 Shipping 139 Seo 50 Shipping 140 Patel 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 141 Rajs 50 Shipping 142 Davies 50 Shipping 143 Matos 50 Shipping 144 Vargas 50 Shipping 180 Taylor 50 Shipping 181 Fleaur 50 Shipping 182 Sullivan 50 Shipping 183 Geoni 50 Shipping 184 Sarchand 50 Shipping 185 Bull 50 Shipping 186 Dellinger 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 187 Cabrio 50 Shipping 188 Chung 50 Shipping 189 Dilly 50 Shipping 190 Gates 50 Shipping 191 Perkins 50 Shipping 192 Bell 50 Shipping 193 Everett 50 Shipping 194 McCain 50 Shipping 195 Jones 50 Shipping 196 Walsh 50 Shipping 197 Feeney 50 Shipping EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 104 Ernst 60 IT 103 Hunold 60 IT 107 Lorentz 60 IT 106 Pataballa 60 IT 105 Austin 60 IT 204 Baer 70 Public Relation s 176 Taylor 80 Sales 177 Livingston 80 Sales 179 Johnson 80 Sales EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 175 Hutton 80 Sales 174 Abel 80 Sales 173 Kumar 80 Sales 172 Bates 80 Sales 171 Smith 80 Sales 170 Fox 80 Sales 169 Bloom 80 Sales 168 Ozer 80 Sales 145 Russell 80 Sales 146 Partners 80 Sales 147 Errazuriz 80 Sales EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 148 Cambrault 80 Sales 149 Zlotkey 80 Sales 150 Tucker 80 Sales 151 Bernstein 80 Sales 152 Hall 80 Sales 153 Olsen 80 Sales 154 Cambrault 80 Sales 155 Tuvault 80 Sales 156 King 80 Sales 157 Sully 80 Sales 158 McEwen 80 Sales EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 159 Smith 80 Sales 160 Doran 80 Sales 161 Sewall 80 Sales 162 Vishney 80 Sales 163 Greene 80 Sales 164 Marvins 80 Sales 165 Lee 80 Sales 166 Ande 80 Sales 167 Banda 80 Sales 101 Kochhar 90 Executive 100 King 90 Executive EMPLOYEE_ID LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME ----------- ------------------------- ------------- --------------- 102 De Haan 90 Executive 110 Chen 100 Finance 108 Greenberg 100 Finance 111 Sciarra 100 Finance 112 Urman 100 Finance 113 Popp 100 Finance 109 Faviet 100 Finance 206 Gietz 110 Accounting 205 Higgins 110 Accounting 106 rows selected.
错误别名用法
SQL> SELECT e.employee_id,e.last_name,d.department_id,d.department_name FROM employees e,departments d WHERE employees.department_id = d.department_id; SELECT e.employee_id,e.last_name,d.department_id,d.department_name FROM employees e,departments d WHERE employees.department_id = d.department_id * ERROR at line 1: ORA-00904: "EMPLOYEES"."DEPARTMENT_ID": invalid identifier