oracle sql select语句的使用方法

select格式：
SELECT [ ALL ｜ DISTINCT ] <字段表达式1[,<字段表达式2[,…]
FROM <表名1>,<表名2>[，…]
[WHERE <筛选择条件表达式>]
[GROUP BY <分组表达式> [HAVING<分组条件表达式>]]
[ORDER BY <字段>[ASC ｜ DESC]]

语句说明：
[]方括号为可选项
[GROUP BY <分组表达式> [HAVING<分组条件表达式>]]
指将结果按<分组表达式>的值进行分组，该值相等的记录为一组，带【HAVING】
短语则只有满足指定条件的组才会输出。
[ORDER BY <字段>[ASC ｜ DESC]]
显示结果要按<字段>值升序或降序进行排序

练习：
1:表hkb_test_sore取出成绩sore前5名的记录，
2:取第5名的记录

1，答案select a.sore_id, a.sore
from (select * from hkb_test_sore order by sore desc) a
where rownum <=5

2，答案select a.sore_id, a.sore
from (select * from hkb_test_sore order by sore desc) a
where rownum <=5
minus
select a.sore_id, a.sore
from (select * from hkb_test_sore order by sore desc) a
where rownum <=4;
3：查询两个分数一样的记录
select *
from hkb_test_sore a
where a.sore = (select sore
                   from hkb_test_sore a
                  group by a.sore
                 having count(a.sore) = 2);

union,union all,intersect,minus的区别：
SQL> select * from hkb_test2;
X        Y
---- -----
a        1
b        2
c        3
g        4

SQL> select * from hkb_test3;
X        Y
---- -----
a        1
b        2
e        3
f        4

SQL> select * from hkb_test2;
X        Y
---- -----
a        1
b        2
c        3
g        4

SQL> select * from hkb_test3;
X        Y
---- -----
a        1
b        2
e        3
f        4

SQL> select * from hkb_test2
2 union
3 select * from hkb_test3;
X        Y
---- -----
a        1
b        2
c        3
e        3
f        4
g        4

6 rows selected

SQL> select * from hkb_test2
2 union all
3 select * from hkb_test3;
X        Y
---- -----
a        1
b        2
c        3
g        4
a        1
b        2
e        3
f        4

8 rows selected

SQL> select * from hkb_test2
2 intersect
3 select * from hkb_test3;
X        Y
---- -----
a        1
b        2

SQL> select * from hkb_test2
2 minus
3 select * from hkb_test3;
X        Y
---- -----
c        3
g        4

综合上面实例看个完整的实例

SQL>
SQL>
SQL> -- create demo table
SQL> create table Employee(
2    ID                 VARCHAR2(4 BYTE)         NOT NULL primary key,
3    First_Name         VARCHAR2(10 BYTE),
4    Last_Name          VARCHAR2(10 BYTE),
5    Start_Date         DATE,
6    End_Date           DATE,
7    Salary             Number(8,2),
8    City               VARCHAR2(10 BYTE),
9    Description        VARCHAR2(15 BYTE)
10 )
11 /

Table created.

SQL>
SQL> -- prepare data
SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,       Description)
2               values ('01','Jason',    'Martin', to_date('19960725','YYYYMMDD'), to_date('20060725','YYYYMMDD'), 1234.56, 'Toronto', 'Programmer')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,       Description)
2                values('02','Alison',   'Mathews', to_date('19760321','YYYYMMDD'), to_date('19860221','YYYYMMDD'), 6661.78, 'Vancouver','Tester')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,       Description)
2                values('03','James',    'Smith',   to_date('19781212','YYYYMMDD'), to_date('19900315','YYYYMMDD'), 6544.78, 'Vancouver','Tester')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,       Description)
2                values('04','Celia',    'Rice',    to_date('19821024','YYYYMMDD'), to_date('19990421','YYYYMMDD'), 2344.78, 'Vancouver','Manager')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,       Description)
2                values('05','Robert',   'Black',   to_date('19840115','YYYYMMDD'), to_date('19980808','YYYYMMDD'), 2334.78, 'Vancouver','Tester')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
2                values('06','Linda',    'Green',   to_date('19870730','YYYYMMDD'), to_date('19960104','YYYYMMDD'), 4322.78,'New York', 'Tester')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
2                values('07','David',    'Larry',   to_date('19901231','YYYYMMDD'), to_date('19980212','YYYYMMDD'), 7897.78,'New York', 'Manager')
3 /

1 row created.

SQL> insert into Employee(ID, First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
2                values('08','James',    'Cat',     to_date('19960917','YYYYMMDD'), to_date('20020415','YYYYMMDD'), 1232.78,'Vancouver', 'Tester')
3 /

1 row created.

SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select * from Employee
2 /

ID   FIRST_NAME           LAST_NAME            START_DAT END_DATE      SALARY CITY       DESCRIPTION
---- -------------------- -------------------- --------- --------- ---------- ---------- ---------------
01   Jason                Martin               25-JUL-96 25-JUL-06    1234.56 Toronto    Programmer
02   Alison               Mathews              21-MAR-76 21-FEB-86    6661.78 Vancouver Tester
03   James                Smith                12-DEC-78 15-MAR-90    6544.78 Vancouver Tester
04   Celia                Rice                 24-OCT-82 21-APR-99    2344.78 Vancouver Manager
05   Robert               Black                15-JAN-84 08-AUG-98    2334.78 Vancouver Tester
06   Linda                Green                30-JUL-87 04-JAN-96    4322.78 New York   Tester
07   David                Larry                31-DEC-90 12-FEB-98    7897.78 New York   Manager
08   James                Cat                  17-SEP-96 15-APR-02    1232.78 Vancouver Tester

8 rows selected.

SQL>
SQL>
SQL> SELECT id, first_name, last_name FROM employee
2 /

ID   FIRST_NAME           LAST_NAME
---- -------------------- --------------------
01   Jason                Martin
02   Alison               Mathews
03   James                Smith
04   Celia                Rice
05   Robert               Black
06   Linda                Green
07   David                Larry
08   James                Cat

8 rows selected.

在ORACLE中实现SELECT TOP N的方法
1.在ORACLE中实现SELECT TOP N

由于ORACLE不支持SELECT TOP语句，所以在ORACLE中经常是用ORDER BY跟ROWNUM的组合来实现SELECT TOP N的查询。

简单地说，实现方法如下所示：

   SELECT　列名１．．．列名ｎ　FROM

     (SELECT　列名１．．．列名ｎ　FROM 表名 ORDER BY 列名１．．．列名ｎ)

    WHERE ROWNUM <= N（抽出记录数）

   ORDER BY ROWNUM ASC

    下面举个例子简单说明一下。

   顾客表customer(id,name)有如下数据：

   ID NAME

    01 first

    02 Second

    03 third

    04 forth

    05 fifth

    06 sixth

    07 seventh

    08 eighth

    09 ninth

    10 tenth

    11 last

    则按NAME的字母顺抽出前三个顾客的SQL语句如下所示：

   SELECT * FROM

     (SELECT * FROM CUSTOMER ORDER BY NAME)

    WHERE ROWNUM <= 3

    ORDER BY ROWNUM ASC

    输出结果为：

   ID NAME

    08 eighth

    05 fifth

    01 first

2.在TOP N纪录中抽出第M（M <= N）条记录

在得到了TOP N的数据之后，为了抽出这N条记录中的第M条记录，我们可以考虑从ROWNUM着手。我们知道，ROWNUM是记录表中数据编号的一个隐藏子段，所以可以在得到TOP N条记录的时候同时抽出记录的ROWNUM，然后再从这N条记录中抽取记录编号为M的记录，即使我们希望得到的结果。

从上面的分析可以很容易得到下面的SQL语句。

SELECT 列名１．．．列名ｎ FROM

      (

      SELECT ROWNUM RECNO, 列名１．．．列名ｎFROM

        (SELECT 列名１．．．列名ｎ FROM 表名 ORDER BY 列名１．．．列名ｎ)

      WHERE ROWNUM <= N（抽出记录数）

    ORDER BY ROWNUM ASC

      )

    WHERE RECNO = M（M <= N）

同样以上表的数据为基础，那么得到以NAME的字母顺排序的第二个顾客的信息的SQL语句应该这样写：

    SELECT ID, NAME FROM

      (

       SELECT ROWNUM RECNO, ID, NAME FROM

         (SELECT * FROM CUSTOMER ORDER BY NAME)

          WHERE ROWNUM <= 3

          ORDER BY ROWNUM ASC )

        WHERE RECNO = 2

      结果则为：

    ID NAME

     05 fifth

3.抽出按某种方式排序的记录集中的第N条记录

在2的说明中，当M = N的时候，即为我们的标题讲的结果。实际上，2的做法在里面N>M的部分的数据是基本上不会用到的，我们仅仅是为了说明方便而采用。

如上所述，则SQL语句应为：

SELECT 列名１．．．列名ｎ FROM

      (

       SELECT ROWNUM RECNO, 列名１．．．列名ｎFROM

         (SELECT 列名１．．．列名ｎ FROM 表名 ORDER BY 列名１．．．列名ｎ)

          WHERE ROWNUM <= N（抽出记录数）

       ORDER BY ROWNUM ASC

      )

      WHERE RECNO = N

那么，2中的例子的SQL语句则为：

     SELECT ID, NAME FROM

       (

        SELECT ROWNUM RECNO, ID, NAME FROM

          (SELECT * FROM CUSTOMER ORDER BY NAME)

        WHERE ROWNUM <= 2

        ORDER BY ROWNUM ASC

       )

       WHERE RECNO = 2

结果为：

ID NAME

05 fifth

4.抽出按某种方式排序的记录集中的第M条记录开始的X条记录

3里所讲得仅仅是抽取一条记录的情况，当我们需要抽取多条记录的时候，此时在2中的N的取值应该是在N >= (M + X - 1)这个范围内，当让最经济的取值就是取等好的时候了的时候了。当然最后的抽取条件也不是RECNO = N了，应该是RECNO BETWEEN M AND (M + X - 1)了，所以随之而来的SQL语句则为：

    SELECT 列名１．．．列名ｎ FROM

     (

      SELECT ROWNUM RECNO, 列名１．．．列名ｎFROM

       (

       SELECT 列名１．．．列名ｎ FROM 表名 ORDER BY 列名１．．．列名ｎ)

       WHERE ROWNUM <= N （N >= (M + X - 1)）

     ORDER BY ROWNUM ASC

       )

      WHERE RECNO BETWEEN M AND (M + X - 1)

同样以上面的数据为例，则抽取NAME的字母顺的第2条记录开始的3条记录的SQL语句为：

    SELECT ID, NAME FROM

      (

       SELECT ROWNUM RECNO, ID, NAME FROM

         (SELECT * FROM CUSTOMER ORDER BY NAME)

       WHERE ROWNUM <= (2 + 3 - 1)

       ORDER BY ROWNUM ASC

      )

      WHERE RECNO BETWEEN 2 AND (2 + 3 - 1)

注意:

sql各子句的执行顺序：

1. FROM
2. WHERE
3. GROUP BY
4. HAVING
5. SELECT
6. ORDER BY

补充：数据库,Oracle教程