Oracle SQL - Not and parentheses

Introduction

It is a good idea to use parentheses to specify the precise scope of the NOT operator explicitly.

select  code, category, duration 
from    courses 
where   (category = 'BLD' or  duration = 2) 
and not (category = 'BLD' and duration = 2); 
  

Just as in mathematics, you can eliminate parentheses from SQL expressions.

The following two queries are logically equivalent:

select * from emp where NOT (ename = 'BLAKE' AND init = 'R') 
select * from emp where      ename <> 'BLAKE' OR init <> 'R' 
  

In the second version, the NOT operator disappeared, the negation is applied to the two comparison operators.

Demo

SQL>
SQL> drop table emp;

Table dropped.-- from w w w . j a v a 2s  .  com

SQL> create table emp(
  2  empno      NUMBER(4)    primary key,
  3  ename      VARCHAR2(8)  not null   ,
  4  init       VARCHAR2(5)  not null   ,
  5  job        VARCHAR2(8)             ,
  6  mgr        NUMBER(4)               ,
  7  bdate      DATE         not null   ,
  8  msal       NUMBER(6,2)  not null   ,
  9  comm       NUMBER(6,2)             ,
 10  deptno     NUMBER(2)    default 10) ;
SQL>
SQL> insert into emp values(7001,'SMITH','N',  'TRAINER', 7902,date '1975-12-17',  1800 , NULL, 20);
SQL> insert into emp values(7002,'ALLEN','JAM','SALESREP',7006,date '1971-05-20',  1600, 300,   30);
SQL> insert into emp values(7003,'WARD', 'TF' ,'SALESREP',7006,date '1972-03-02',  1250, 500,   10);
SQL> insert into emp values(7004,'JACK', 'JM', 'MANAGER', 7009,date '1977-04-02',  2975, NULL,  20);
SQL> insert into emp values(7005,'BROWN','P',  'SALESREP',7006,date '1976-09-28',  1250, 1400,  30);
SQL> insert into emp values(7006,'BLAKE','R',  'MANAGER', 7009,date '1973-11-01',  2850, NULL,  10);
SQL> insert into emp values(7007,'CLARK','AB', 'MANAGER', 7009,date '1975-06-09',  2450, NULL,  10);
SQL> insert into emp values(7008,'SCOTT','DEF','TRAINER', 7004,date '1979-11-26',  3000, NULL,  20);
SQL> insert into emp values(7009,'KING', 'CC', 'DIRECTOR',NULL,date '1972-10-17',  5000, NULL,  10);
SQL> insert into emp values(7010,'BREAD','JJ', 'SALESREP',7006,date '1978-09-28',  1500, 0,     30);
SQL> insert into emp values(7011,'ADAMS','AA', 'TRAINER', 7008,date '1976-12-30',  1100, NULL,  20);
SQL> insert into emp values(7012,'JONES','R',  'ADMIN',   7006,date '1979-10-03',  8000, NULL,  30);
SQL> insert into emp values(7902,'FORD', 'MG', 'TRAINER', 7004,date '1979-02-13',  3000, NULL,  20);
SQL> insert into emp values(7934,'MARY', 'ABC','ADMIN',   7007,date '1972-01-23',  1300, NULL,  10);
SQL>
SQL>
SQL> drop table courses;

Table dropped.

SQL> create table courses(
  2  code        VARCHAR2(6)  primary key,
  3  description VARCHAR2(30) not null,
  4  category    CHAR(3)      not null,
  5  duration    NUMBER(2)    not null) ;
SQL> insert into courses values('SQL','Introduction to SQL',         'GEN',4);
SQL> insert into courses values('JSON','Oracle for application users','GEN',1);
SQL> insert into courses values('JAVA','Java for Oracle developers',  'BLD',4);
SQL> insert into courses values('PLS','Introduction to PL/SQL',      'BLD',1);
SQL> insert into courses values('XML','XML for Oracle developers',   'BLD',2);
SQL> insert into courses values('ERM','Data modeling with ERM',      'DSG',3);
SQL> insert into courses values('PMT','Process modeling techniques', 'DSG',1);
SQL> insert into courses values('RSD','Relational system design',    'DEF',2);
SQL> insert into courses values('PRO','Prototyping',                 'DSG',5);
SQL> insert into courses values('GEN','System generation',           'DSG',4);
SQL>
SQL> select  code, category, duration
  2  from    courses
  3  where   (category = 'BLD' or  duration = 2)
  4  and not (category = 'BLD' and duration = 2);

CODE   | CAT |  DURATION
------ | --- | ---------
JAVA   | BLD |  00004.00
PLS    | BLD |  00001.00
RSD    | DEF |  00002.00

SQL>
SQL> select * from emp where NOT (ename = 'BLAKE' AND init = 'R')
  2
SQL> select * from emp where      ename <> 'BLAKE' OR init <> 'R'
  2

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