selet *
from ** left outer join ** on **
where **=**
对同一张表
优先处理left outer join ** on ** 还是where **=**
from ** left outer join ** on **
where **=**
对同一张表
优先处理left outer join ** on ** 还是where **=**
解决方案 »
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SQL> with a as (select * from emp where empno=7499)
2 select * from a full join emp b on a.mgr=b.mgr
3 ;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ----------- ---------- ---------- ---------- ----- ---------- --------- ----- ----------- --------- --------- ------
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7900 JAMES CLERK 7698 1981-12-3 950.00 30
7839 KING PRESIDENT 1981-11-17 5000.00 10
7782 CLARK MANAGER 7839 1981-6-9 2450.00 10
7698 BLAKE MANAGER 7839 1981-5-1 2850.00 30
7566 JONES MANAGER 7839 1981-4-2 2975.00 20
7934 MILLER CLERK 7782 1982-1-23 1300.00 10
7876 ADAMS CLERK 7788 1987-5-23 1100.00 20
7902 FORD ANALYST 7566 1981-12-3 3000.00 20
7788 SCOTT ANALYST 7566 1987-4-19 3000.00 20
7369 SMITH CLERK 7902 1980-12-17 800.10 20
14 rows selected
SQL> select * from emp a full join emp b on a.mgr=b.mgr where a.empno=7499;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ----------- ---------- ---------- ---------- ----- ---------- --------- ----- ----------- --------- --------- ------
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7499 ALLEN SALESMAN 7698 1981-2-20 1600.00 300.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7521 WARD SALESMAN 7698 1981-2-22 1250.00 500.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7654 MARTIN SALESMAN 7698 1981-9-28 1250.00 1400.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7844 TURNER SALESMAN 7698 1981-9-8 1500.00 0.00 30
7499 ALLEN SALESMAN 7698 1981-2-20 1600 300 30 7900 JAMES CLERK 7698 1981-12-3 950.00 30
SQL>
2、where子句基于指定的条件对记录行进行筛选;
3、group by子句将数据划分为多个分组;
4、使用聚集函数进行计算;
5、使用having子句筛选分组;
6、计算所有的表达式;
7、使用order by对结果集进行排序。
8、执行select。