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标题 oracle sql select语句的使用方法
范文
    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)
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更新时间：2025/5/13 9:02:47