Oracle SQL多表查询

曾经一段时间我对oracle的多表查询搞的云里雾里，究其原因：oracle自己的语法和SQL国际标准语法混用。此文章仅适合oracle 菜鸟，老鸟直接飞过…

多表连接类型（SQL 1999标准）

 

 

• Cross joins

• Natural joins

• USING clause

• Full (or two-sided) outer joins

• Arbitrary join conditions for outer joins

SQL1999语法：

SELECT table1.column, table2.column

FROM table1

[CROSS JOIN table2] |

[NATURAL JOIN table2] |

[JOIN table2 USING (column_name)] |

[JOIN table2

ON (table1.column_name = table2.column_name)]|

[LEFT|RIGHT|FULL OUTER JOIN table2

ON (table1.column_name = table2.column_name)]|

[CROSS JOIN table2];

语法解释：

table1.column --指明从中检索数据的表和列

CROSS JOIN --返回两个表的笛卡尔集

NATURAL JOIN --根据相同的列名连接两个表

JOIN table

USING column_name --根据列名执行等值连接

JOIN table ON

table1.column_name --根据ON 子句中的条件执行等值连接

= table2.column_name

LEFT/RIGHT/FULL OUTER

一般来说，从数据显示方式来讲，分为内连接和外连接

内连接：只返回满足连接条件的数据。

外连接：除了返回满足连接条的行以外，还返回左（右）表中，不满足条件的行，

称为左（右）连接

演示，主要以SQL标准为主，oracle 写法作对比。示例用户为scott、HR

解锁这两个用户语句：

alter user scott identified by tiger account unlock;

alter user hr identified by hr account unlock;

内连接

 

 

--Oracle的写法

select empno,ename,sal,dname,loc from emp,dept

where emp.deptno=dept.deptno;

-- SQL 99标准的写法

select empno,ename,job,sal,dept.deptno,dname,loc

from emp join dept on emp.deptno=dept.deptno;

或把join改为inner join

外连接

左外连接

 

 

Oracle 外连接语法：

SELECT table1.column, table2.column --右外连接

FROM table1, table2

WHERE table1.column(+) = table2.column;

SELECT table1.column, table2.column --左外连接

FROM table1, table2

WHERE table1.column = table2.column(+);

SQL 1999标准外连接语法见上面SQL1999语法

--Oracle的写法

外连接的符号是（＋），（＋）要放在字段名后。（＋）对面的那个表，会全部显示。

左外连接时，加号在等号的右边

SQL> select d.dname,e.ename,e.deptno

from dept d,emp e

where d.deptno = e.deptno(+)

order by d.deptno;

DNAME ENAME DEPTNO

-------------- ---------- ------

ACCOUNTING CLARK 10

ACCOUNTING KING 10

ACCOUNTING MILLER 10

RESEARCH JONES 20

RESEARCH FORD 20

RESEARCH ADAMS 20

RESEARCH SMITH 20

RESEARCH SCOTT 20

SALES WARD 30

SALES TURNER 30

SALES ALLEN 30

SALES JAMES 30

SALES BLAKE 30

SALES MARTIN 30

OPERATIONS

15 rows selected

-- SQL 99标准的写法接

SQL> select d.dname,e.ename,e.deptno

from dept d

left join emp e

on d.deptno = e.deptno

order by d.deptno;

DNAME ENAME DEPTNO

-------------- ---------- ------

ACCOUNTING CLARK 10

ACCOUNTING KING 10

ACCOUNTING MILLER 10

RESEARCH JONES 20

RESEARCH FORD 20

RESEARCH ADAMS 20

RESEARCH SMITH 20

RESEARCH SCOTT 20

SALES WARD 30

SALES TURNER 30

SALES ALLEN 30

SALES JAMES 30

SALES BLAKE 30

SALES MARTIN 30

OPERATIONS

15 rows selected

右外连接

 

 

--oracle的写法

SQL> select empno, ename, job, sal, dept.deptno, dname, loc

2 from emp, dept

3 where emp.deptno(+) = dept.deptno;

EMPNO ENAME JOB SAL DEPTNO DNAME LOC

----- ---------- --------- --------- ------ -------------- -------------

7782 CLARK MANAGER 2450.00 10 ACCOUNTING NEW YORK

7839 KING PRESIDENT 5000.00 10 ACCOUNTING NEW YORK

7934 MILLER CLERK 1300.00 10 ACCOUNTING NEW YORK

7566 JONES MANAGER 2975.00 20 RESEARCH DALLAS

7902 FORD ANALYST 3000.00 20 RESEARCH DALLAS

7876 ADAMS CLERK 1100.00 20 RESEARCH DALLAS

7369 SMITH CLERK 800.00 20 RESEARCH DALLAS

7788 SCOTT ANALYST 3000.00 20 RESEARCH DALLAS

7521 WARD SALESMAN 1250.00 30 SALES CHICAGO

7844 TURNER SALESMAN 1500.00 30 SALES CHICAGO

7499 ALLEN SALESMAN 1600.00 30 SALES CHICAGO

7900 JAMES CLERK 950.00 30 SALES CHICAGO

7698 BLAKE MANAGER 2850.00 30 SALES CHICAGO

7654 MARTIN SALESMAN 1250.00 30 SALES CHICAGO

40 OPERATIONS BOSTON

15 rows selected

--SQL1999标准写法

SQL> select empno, ename, job, sal, dept.deptno, dname, loc

2 from emp

3 right join dept

4 on emp.deptno = dept.deptno;

EMPNO ENAME JOB SAL DEPTNO DNAME LOC

----- ---------- --------- --------- ------ -------------- -------------

7782 CLARK MANAGER 2450.00 10 ACCOUNTING NEW YORK

7839 KING PRESIDENT 5000.00 10 ACCOUNTING NEW YORK

7934 MILLER CLERK 1300.00 10 ACCOUNTING NEW YORK

7566 JONES MANAGER 2975.00 20 RESEARCH DALLAS

7902 FORD ANALYST 3000.00 20 RESEARCH DALLAS

7876 ADAMS CLERK 1100.00 20 RESEARCH DALLAS

7369 SMITH CLERK 800.00 20 RESEARCH DALLAS

7788 SCOTT ANALYST 3000.00 20 RESEARCH DALLAS

7521 WARD SALESMAN 1250.00 30 SALES CHICAGO

7844 TURNER SALESMAN 1500.00 30 SALES CHICAGO

7499 ALLEN SALESMAN 1600.00 30 SALES CHICAGO

7900 JAMES CLERK 950.00 30 SALES CHICAGO

7698 BLAKE MANAGER 2850.00 30 SALES CHICAGO

7654 MARTIN SALESMAN 1250.00 30 SALES CHICAGO

40 OPERATIONS BOSTON

15 rows selected

全连接

 

 

--SQL1999标准写法

SQL> select empno, ename, job, sal, d.deptno, dname, loc

2 from emp e

3 full join dept d

4 on e.deptno = d.deptno;

EMPNO ENAME JOB SAL DEPTNO DNAME LOC

----- ---------- --------- --------- ------ -------------- -------------

7369 SMITH CLERK 800.00 20 RESEARCH DALLAS

7499 ALLEN SALESMAN 1600.00 30 SALES CHICAGO

7521 WARD SALESMAN 1250.00 30 SALES CHICAGO

7566 JONES MANAGER 2975.00 20 RESEARCH DALLAS

7654 MARTIN SALESMAN 1250.00 30 SALES CHICAGO

7698 BLAKE MANAGER 2850.00 30 SALES CHICAGO

7782 CLARK MANAGER 2450.00 10 ACCOUNTING NEW YORK

7788 SCOTT ANALYST 3000.00 20 RESEARCH DALLAS

7839 KING PRESIDENT 5000.00 10 ACCOUNTING NEW YORK

7844 TURNER SALESMAN 1500.00 30 SALES CHICAGO

7876 ADAMS CLERK 1100.00 20 RESEARCH DALLAS

7900 JAMES CLERK 950.00 30 SALES CHICAGO

7902 FORD ANALYST 3000.00 20 RESEARCH DALLAS

7934 MILLER CLERK 1300.00 10 ACCOUNTING NEW YORK

40 OPERATIONS BOSTON

15 rows selected

自连接

 

 

把表自身的镜像当成另外一个表

--oracle 的写法

SQL> select e.ename || ' works for ' || m.ename

2 from emp e, emp m

3 where e.empno = m.mgr;

E.ENAME||'WORKSFOR'||M.ENAME

-------------------------------

JONES works for FORD

JONES works for SCOTT

BLAKE works for TURNER

BLAKE works for ALLEN

BLAKE works for WARD

BLAKE works for JAMES

BLAKE works for MARTIN

CLARK works for MILLER

SCOTT works for ADAMS

KING works for BLAKE

KING works for JONES

KING works for CLARK

FORD works for SMITH

13 rows selected

--SQL1999标准的写法

SQL> select e.ename || ' works for ' || m.ename

2 from emp e

3 join emp m

4 on e.empno = m.mgr;

E.ENAME||'WORKSFOR'||M.ENAME

-------------------------------

JONES works for FORD

JONES works for SCOTT

BLAKE works for TURNER

BLAKE works for ALLEN

BLAKE works for WARD

BLAKE works for JAMES

BLAKE works for MARTIN

CLARK works for MILLER

SCOTT works for ADAMS

KING works for BLAKE

KING works for JONES

KING works for CLARK

FORD works for SMITH

13 rows selected

自然连接

 

 

以两个表具有相同的字段的所有列为基础，可采用自然连接（natural join)

它将选择两个表中那些在所有匹配的列中值相等的行。

如果列具有相同的名称，但数据类型能够不同，则会报错。

--SQL1999标准写法

SQL> select empno, ename, job, sal, deptno, dname, loc

2 from emp natural

3 join dept;

EMPNO ENAME JOB SAL DEPTNO DNAME LOC

----- ---------- --------- --------- ------ -------------- -------------

7782 CLARK MANAGER 2450.00 10 ACCOUNTING NEW YORK

7839 KING PRESIDENT 5000.00 10 ACCOUNTING NEW YORK

7934 MILLER CLERK 1300.00 10 ACCOUNTING NEW YORK

7566 JONES MANAGER 2975.00 20 RESEARCH DALLAS

7902 FORD ANALYST 3000.00 20 RESEARCH DALLAS

7876 ADAMS CLERK 1100.00 20 RESEARCH DALLAS

7369 SMITH CLERK 800.00 20 RESEARCH DALLAS

7788 SCOTT ANALYST 3000.00 20 RESEARCH DALLAS

7521 WARD SALESMAN 1250.00 30 SALES CHICAGO

7844 TURNER SALESMAN 1500.00 30 SALES CHICAGO

7499 ALLEN SALESMAN 1600.00 30 SALES CHICAGO

7900 JAMES CLERK 950.00 30 SALES CHICAGO

7698 BLAKE MANAGER 2850.00 30 SALES CHICAGO

7654 MARTIN SALESMAN 1250.00 30 SALES CHICAGO

14 rows selected

使用using子句创建连接

 

 

如果几个列具有相同的名称，但是数据类型不匹配，那么可以使用using子句来修改natural join子句以指定要用于等值连接的列，在多个列匹配时，使用using 子句只匹配一个列，在引用列中不要使用表名或别名。natural join 和using 子句是互不相容的。

SELECT l.city, d.department_name

FROM locations l JOIN departments d USING (location_id)

WHERE location_id = 1400;

--下面的语句无效，因为where 子句中限定了location_id为d. location_id

SELECT l.city, d.department_name

FROM locations l JOIN departments d USING (location_id)

WHERE d.location_id = 1400;

ORA-25154: column part of USING clause cannot have qualifier

注意：两个表中名称相同的列在使用时不能有任何限定符，这一限制同样适用natural join

cross join 实现交叉连接

交叉连接产生的结果集也就是笛卡尔乘积

--oracle 的写法

select empno, ename, dname

from emp,dept;

在oracle语法中直接from两张表就是cross join

--SQL1999标准写法

select empno, ename, dname

from emp

cross join dept;

等值连接时增加条件

 

 

上述的多表连接都是等值连接（最常用），等值连接后面还可以添加限定条件。

--oracle 的写法

select e.empno, e.ename, d.dname

from emp e, dept d

where d.deptno = e.deptno

and e.ename = 'SCOTT';

--SQL1999标准的写法

select e.empno, e.ename, d.dname

from emp e

inner join dept d

on d.deptno = e.deptno

and e.ename = 'SCOTT';

非等值连接

 

 

--oracle的写法

select ename, sal, grade

from emp, salgrade

where sal between losal and hisal

and emp.deptno = 20;

--SQL1999标准写法

select e.ename, e.sal, s.grade

from emp e

join salgrade s

on e.sal between losal and hisal

and e.deptno = 20;

总结

 

 

Oracle的语法还是比较人性化的，除了左外连接和右外连接。如果想使代码简单明了，使用oracle的语法，如果想使写出的代码兼容性比较好（可能会移植到DB2等），尽量使用SQL标准语法。

详细信息请参考oracle 官方文档

Oracle® Database

SQL Language Reference

11g Release 2 (11.2)

E17118-04

9 SQL Queries and Subqueries 部分