Oracle PL/SQL/Subquery/Virtual Table
First three rows from subquery
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SQL> SQL> create table history
2 ( empno NUMBER(4) 3 , beginyear NUMBER(4) 4 , begindate DATE 5 , enddate DATE 6 , deptno NUMBER(2) 7 , sal NUMBER(6,2) 8 , comments VARCHAR2(60) 9 , constraint H_PK primary key (empno,begindate) 10 , constraint H_BEG_END check (begindate < enddate) 11 ) ;
Table created. SQL> SQL> SQL> alter session set NLS_DATE_FORMAT="DD-MM-YYYY"; Session altered. SQL> SQL> insert into history values (1,2000,"01-02-2000", NULL ,20, 800,"restarted"); 1 row created. SQL> insert into history values (2,1995,"01-10-1995","01-11-2009",30,1700,""); 1 row created. SQL> insert into history values (2,2009,"01-11-2009", NULL ,30,1600,"just hired"); 1 row created. SQL> insert into history values (3,1986,"01-10-1986","01-08-1987",20,1000,""); 1 row created. SQL> insert into history values (3,1987,"01-08-1987","01-01-1989",30,1000,"On training"); 1 row created. SQL> insert into history values (3,2000,"01-02-2000", NULL ,30,1250,""); 1 row created. SQL> SQL> select *
2 from (select empno, sal
3 from history
4 order by sal desc)
5 where rownum <= 3;
EMPNO SAL
----------
2 1700
2 1600
3 1250
SQL> SQL> drop table history; Table dropped. SQL>
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Format result from subquery
<source lang="sql">
SQL> SQL> SQL> select username,
2 to_number( substr( data, 1, 10 ) ) cnt, 3 to_number( substr( data, 11 ) ) avg 4 from ( 5 select a.username, (select to_char( count(*), "fm0000000009" ) || avg(object_id) from all_objects b where b.owner = a.username) data 6 from all_users a 7 ) 8 /
USERNAME CNT AVG
---------- ----------
SYS 6520 5009.74064 SYSTEM 422 6095.87678 OUTLN 7 1172.57143 DIP 0 TSMSYS 2 8606.5 INV15 2 16237.5 DBSNMP 46 9592.65217 INV10 2 16227.5 CTXSYS 338 9877.92012 XDB 334 10800.7485 ANONYMOUS 0 USERNAME CNT AVG
---------- ----------
MDSYS 458 11667.2009 HR 34 12104.5 FLOWS_FILES 11 12717.2727 FLOWS_020100 1085 12813.424 sqle 530 16254.6849 INV11 2 16229.5 INV12 2 16231.5 INV13 2 16233.5 INV14 2 16235.5 PLSQL 0 INV16 2 16239.5 USERNAME CNT AVG
---------- ----------
INV17 2 16241.5 INV18 2 16243.5 INV19 2 16245.5 INV20 2 16247.5 DEFINER 4 16250.5 27 rows selected. SQL>
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Select from virtual table (sub query) with rownum
<source lang="sql">
SQL> SQL> SQL> -- create demo table SQL> create table Employee(
2 ID VARCHAR2(4 BYTE) NOT NULL, 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"), 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("03","James", "Smith", to_date("19781212","YYYYMMDD"), to_date("19900315","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("04","Celia", "Rice", to_date("19821024","YYYYMMDD"), to_date("19990421","YYYYMMDD"), 2334.78, "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"), 2334.78,"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"), 2334.78,"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"), 2334.78,"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 2334.78 Vancouver Tester 03 James Smith 12-DEC-78 15-MAR-90 2334.78 Vancouver Tester 04 Celia Rice 24-OCT-82 21-APR-99 2334.78 Vancouver Manager 05 Robert Black 15-JAN-84 08-AUG-98 2334.78 Vancouver Tester 06 Linda Green 30-JUL-87 04-JAN-96 2334.78 New York Tester 07 David Larry 31-DEC-90 12-FEB-98 2334.78 New York Manager 08 James Cat 17-SEP-96 15-APR-02 2334.78 Vancouver Tester 8 rows selected. SQL> SQL> -- select from virtual table SQL> SQL> SQL> SELECT id "Emp #", first_name "Name", salary "Salary",
2 ROWNUM rank 3 FROM 4 (SELECT id, first_name, salary FROM employee ORDER BY salary desc);
Emp Name Salary RANK
---------- ---------- ----------
04 Celia 2334.78 1 02 Alison 2334.78 2 03 James 2334.78 3 08 James 2334.78 4 05 Robert 2334.78 5 06 Linda 2334.78 6 07 David 2334.78 7 01 Jason 1234.56 8 8 rows selected. SQL> SQL> SQL> SQL> SQL> SQL> SQL> SQL> -- clean the table SQL> drop table Employee; Table dropped. SQL> SQL>
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