Question

DROP TABLE IF EXISTS product;

Asked by: Peewee

Hi There,
simple question i imagine..

i want to drop my table if it exists so that i can rebuild it.. It fails on the drop command, it doesn't like specified where it is..  Can you tweak or show me a better way?

cheers Peewee

here's what i got so far:

set serveroutput on;
REM lets try testing to see if a table exists

declare
    cursor c is select null from user_tables where table_name = 'PRODUCT';
    x number;
begin
    open c;
    fetch c into x;
    if (c%NOTFOUND) then
        dbms_output.put_line('Product Table Does Not Exist');
        -- Do Nothing
    else
        dbms_output.put_line('Product Table Exists');
        drop table PRODUCT;
    end if;
end;
/

create or replace table PRODUCT (
        upc varchar(15) primary key,
        description varchar(20) not null,
        linespeed number(5) not null,
        price_plan number(5)not null,
        product_count number(3) not null,
        published char(1) default 'N',
        constraint PRODUCT_UQ UNIQUE (product_count),
        constraint published_chk CHECK(published IN('Y','N')),
        constraint linespeed_chk CHECK(linespeed IN(256,512,1000,2000))
);


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Asked On
2005-08-25 at 07:02:47ID21539783
Tags

table

,

exists

,

drop

Topic

Oracle Database

Participating Experts
5
Points
50
Comments
12

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Answers

 

by: PeeweePosted on 2005-08-25 at 07:04:23ID: 14752052

will create or replace work with tables?

 

by: JankovskyPosted on 2005-08-25 at 07:17:22ID: 14752214

create or replace doesnt work for tables.
I'd recommend:

Begin  
  execute immediate 'Drop table PRODUCT';
  Exception when others then null;
End;
/
create or replace table PRODUCT (
        upc varchar(15) primary key,
        description varchar(20) not null,
        linespeed number(5) not null,
        price_plan number(5)not null,
        product_count number(3) not null,
        published char(1) default 'N',
        constraint PRODUCT_UQ UNIQUE (product_count),
        constraint published_chk CHECK(published IN('Y','N')),
        constraint linespeed_chk CHECK(linespeed IN(256,512,1000,2000))
);

 

by: ploubierPosted on 2005-08-25 at 07:17:57ID: 14752219

You can't replace a table. You have to drop it first, then recreate it.

 

by: slightwvPosted on 2005-08-25 at 07:33:45ID: 14752388

If none of the above helps:

I'm not sure why it would matter if the drop fails......

Are you just trying to get a sql script that will not have any 'acceptable' errors in it?  

 

by: awking00Posted on 2005-08-25 at 07:34:02ID: 14752394

DECLARE
v_exist  PLS_INTEGER;
BEGIN
select count(*)
into v_exist
from user_tables
where table_name = 'PRODUCT';

if v_exist = 1 then
execute immediate
'drop table product';
end if;

create table PRODUCT (
        upc varchar(15) primary key,
        description varchar(20) not null,
        linespeed number(5) not null,
        price_plan number(5)not null,
        product_count number(3) not null,
        published char(1) default 'N',
        constraint PRODUCT_UQ UNIQUE (product_count),
        constraint published_chk CHECK(published IN('Y','N')),
        constraint linespeed_chk CHECK(linespeed IN(256,512,1000,2000))
);
END;

 

by: PeeweePosted on 2005-08-25 at 09:07:47ID: 14753427

awking00,
your code doesnt quite work..  it has the same type of error as my original one..

It seems to be that the create table wont work between the BEGIN and END blocks..

Why is this? How do we get around this?
Peewee

PLS-00103: Encountered the symbol "CREATE" when expecting one of the following:
begin case declare end exception exit for goto if loop mod
null pragma raise return select update while with

 

by: slightwvPosted on 2005-08-25 at 09:25:14ID: 14753616

You need to use execute immediate to execute DDL in PL/SQL.

Again,
what is the reason behind dropping and creating tables in PL/SQL?

 

by: PeeweePosted on 2005-08-25 at 09:56:09ID: 14753967

Hi slightwv,
its some automation thing for testing i need to write...

if i place the create table in an execute immediate, how do i escape the default definitions which use single quotes?

 

by: slightwvPosted on 2005-08-25 at 09:58:08ID: 14753992

use 2 single quotes to get 1 (not 1 double quote):

...
published char(1) default ''N'',
...

 

by: awking00Posted on 2005-08-25 at 11:04:16ID: 14754673

Oops! Forgot execute immediate. Note - for conditions using quotes within execute immediate require two single quotes( not double quote).

DECLARE
v_exist  PLS_INTEGER;
BEGIN
select count(*)
into v_exist
from user_tables
where table_name = 'PRODUCT';

if v_exist = 1 then
execute immediate
'drop table product';
end if;

execute immediate
'create table PRODUCT (
        upc varchar(15) primary key,
        description varchar(20) not null,
        linespeed number(5) not null,
        price_plan number(5)not null,
        product_count number(3) not null,
        published char(1) default ''N'',
        constraint PRODUCT_UQ UNIQUE (product_count),
        constraint published_chk CHECK(published IN(''Y'',''N'')),
        constraint linespeed_chk CHECK(linespeed IN(256,512,1000,2000))
)';
END;

 
 

 

by: JankovskyPosted on 2005-08-26 at 03:53:10ID: 14759746

Just to remember above recommendation:

Begin  
  execute immediate 'Drop table PRODUCT';
  Exception when others then null; --excepts possible error when table exists, it's simplier than to query data dictionary
End;
/
--you can keep the CREATE statement out of PL/SQL block to simplify the task
create or replace table PRODUCT (
        upc varchar(15) primary key,
        description varchar(20) not null,
        linespeed number(5) not null,
        price_plan number(5)not null,
        product_count number(3) not null,
        published char(1) default 'N',
        constraint PRODUCT_UQ UNIQUE (product_count),
        constraint published_chk CHECK(published IN('Y','N')),
        constraint linespeed_chk CHECK(linespeed IN(256,512,1000,2000))
);

 

by: DrSQLPosted on 2005-08-26 at 05:39:38ID: 14760260

All,
   I think Jankovsky's code will work, but here is my generic procedure for doing this:

create procedure if_exists_then(Object_to_Check_for in varchar2, statement_to_process in varchar2) is
   Offset number := instr(Object_to_Check_for, '.');
   FoundObject varchar2(30);
begin
    select decode(max(OBJECT_NAME),null,'NO','YES')
      into FoundObject from all_objects
     where object_name = upper(substr(Object_to_Check_for, Offset +1)) and  -- Checking to see if there was a schema name on the object name
           owner = decode(Offset, 0, user,
                             upper(substr(Object_to_Check_for, 1, Offset - 1)));
   if FoundObject = 'YES' then
        execute immediate statement_to_process;
   end if;
end;
/

And to use it:

execute if_exists_then('fred.dino','drop table fred.dino');

And, of course, I have the if_not_exists to see if I need to create something:

create procedure if_not_exists_then(Object_to_Check_for in varchar2, statement_to_process in varchar2) is
   Offset number := instr(Object_to_Check_for, '.');
   FoundObject varchar2(3);
begin
    select decode(max(OBJECT_NAME),null,'NO','YES')
      into FoundObject from all_objects
     where object_name = upper(substr(Object_to_Check_for, Offset +1)) and
           owner = decode(Offset, 0, user,
                             upper(substr(Object_to_Check_for, 1, Offset - 1)));
   if FoundObject = 'NO' then
        execute immediate statement_to_process;
   end if;
end;
/

to use:
execute if_not_exists_then('fred.mysequence','create sequence fred.mysequence')

or:

execute if_not_exists_then('fred.emp',-
'create table emp(empid number, -
  ename varchar2(30),-
  mgr number)')
           

Good luck!
DrSQL

20120131-EE-VQP-002

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