萬盛學電腦網 >> 數據庫 >> oracle教程 >> oracle sql select語句的使用方法
oracle sql select語句的使用方法
select格式：
SELECT [ ALL | DISTINCT ] <字段表達式1[,<字段表達式2[,…]
FROM <表名1>,<表名2>[，…]
[WHERE <篩選擇條件表達式>]
[GROUP BY <分組表達式> [HAVING<分組條件表達式>]]
[ORDER BY <字段>[ASC | DESC]]
語句說明：
[]方括號為可選項
[GROUP BY <分組表達式> [HAVING<分組條件表達式>]]
指將結果按<分組表達式>的值進行分組，該值相等的記錄為一組，帶【HAVING】
短語則只有滿足指定條件的組才會輸出。
[ORDER BY <字段>[ASC | DESC]]
顯示結果要按<字段>值升序或降序進行排序
練習：
1:表hkb_test_sore取出成績sore前5名的記錄，
2:取第5名的記錄
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：查詢兩個分數一樣的記錄
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的區別：
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
綜合上面實例看個完整的實例
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中實現SELECT TOP N的方法
1.在ORACLE中實現SELECT TOP N
由於ORACLE不支持SELECT TOP語句，所以在ORACLE中經常是用ORDER BY跟ROWNUM的組合來實現SELECT TOP N的查詢。
簡單地說，實現方法如下所示：
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(抽出記錄數)
ORDER BY ROWNUM ASC
下面舉個例子簡單說明一下。
顧客表customer(id,name)有
