Oracle PL/SQL Tutorial/Query Select/Introduction

A SELECT with Just a FROM Clause

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  /
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>
SQL> SELECT id, first_name, salary FROM employee
  2  /
ID   FIRST_NAME     SALARY
---- ---------- ----------
01   Jason         1234.56
02   Alison        6661.78
03   James         6544.78
04   Celia         2344.78
05   Robert        2334.78
06   Linda         4322.78
07   David         7897.78
08   James         1232.78
8 rows selected.
SQL>
SQL> -- clean the table
SQL> drop table Employee
  2  /
Table dropped.
SQL>

Subquery with comparison operator

SQL>
SQL>
SQL> SELECT COUNT(*) num_owned, a.owner
  2      FROM dba_objects a
  3      WHERE 100<(SELECT COUNT(*) FROM dba_objects b
  4      WHERE a.owner=b.owner)
  5      GROUP BY a.owner;
 NUM_OWNED OWNER
---------- ------------------------------
       473 MDSYS
      1143 FLOWS_020100
      2769 PUBLIC
       575 sqle
       339 CTXSYS
       449 SYSTEM
       668 XDB
      6631 SYS
8 rows selected.

Using the SQL Operators

The SQL operators allow you to limit rows based on

1. pattern matching of strings,
2. lists of values,
3. ranges of values, and
4. null values.

The SQL operators are listed in the following table:

Operator Description LIKE Matches patterns in strings IN Matches lists of values BETWEEN Matches a range of values IS NULL Matches null values IS NAN New for Oracle10g. Matches the NaN special value, which means "not a number" IS INFINITE New for Oracle10g. Matches infinite BINARY_FLOAT and BINARY_DOUBLE values

You can also use the NOT operator to reverse the meaning of LIKE, IN, BETWEEN, and IS NULL:

1. NOT LIKE
2. NOT IN
3. NOT BETWEEN
4. IS NOT NULL
5. IS NOT NAN
6. IS NOT INFINITE

SQL>
SQL> SELECT COUNT(*) num_owned, a.owner
  2      FROM dba_objects a
  3      WHERE 10<(SELECT COUNT(*) FROM dba_objects b
  4      WHERE a.owner=b.owner)
  5      GROUP BY a.owner;
 NUM_OWNED OWNER
---------- ------------------------------
       473 MDSYS
      1143 FLOWS_020100
      2769 PUBLIC
       575 sqle
       339 CTXSYS
        34 HR
        12 FLOWS_FILES
       449 SYSTEM
        46 DBSNMP
       668 XDB
      6631 SYS
11 rows selected.