I'm writing some migration scripts for an Oracle database, and was hoping Oracle had something similar to MySQL's IF EXISTS construct.
Specifically, whenever I want to drop a table in MySQL, I do something like
DROP TABLE IF EXISTS `table_name`;
This way, if the table doesn't exist, the DROP doesn't produce an error, and the script can continue.
Does Oracle have a similar mechanism? I realize I could use the following query to check if a table exists or not
SELECT * FROM dba_tables where table_name = 'table_name';
but the syntax for tying that together with a DROP is escaping me.
There is no 'DROP TABLE IF EXISTS' in oracle, you would have to do the select statement.
try this (i'm not up on oracle syntax, so if my variables are ify, please forgive me):
declare @count int
select @count=count(*) from all_tables where table_name='Table_name';
if @count>0
BEGIN
DROP TABLE tableName;
END
You could always catch the error yourself.
begin
execute immediate 'drop table mytable';
exception when others then null;
end;
It is considered bad practice to overuse this, similar to empty catch()'es in other languages.
Regards
K
Sadly no, there is no such thing as drop if exists, or CREATE IF NOT EXIST
You could write a plsql script to include the logic there.
http://download.oracle.com/docs/cd/B12037_01/server.101/b10759/statements_9003.htm
I'm not much into Oracle Syntax, but i think @Erich's script would be something like this.
declare
cant integer
begin
select into cant count(*) from dba_tables where table_name='Table_name';
if count>0 then
BEGIN
DROP TABLE tableName;
END IF;
END;
BEGIN
EXECUTE IMMEDIATE 'DROP TABLE "IMS"."MAX" ';
EXCEPTION
WHEN OTHERS THEN
IF SQLCODE != -942 THEN
RAISE;
END IF;
EXECUTE IMMEDIATE '
CREATE TABLE "IMS"."MAX"
( "ID" NUMBER NOT NULL ENABLE,
"NAME" VARCHAR2(20 BYTE),
CONSTRAINT "MAX_PK" PRIMARY KEY ("ID")
USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "SYSAUX" ENABLE
) SEGMENT CREATION IMMEDIATE
PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING
STORAGE(INITIAL 65536 NEXT 1048576 MINEXTENTS 1 MAXEXTENTS 2147483645
PCTINCREASE 0 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT FLASH_CACHE DEFAULT CELL_FLASH_CACHE DEFAULT)
TABLESPACE "SYSAUX" ';
END;
// Doing this code, checks if the table exists and later it creates the table max. this simply works in single compilation
With SQL*PLUS you can also use the WHENEVER SQLERROR command:
WHENEVER SQLERROR CONTINUE NONE
DROP TABLE TABLE_NAME;
WHENEVER SQLERROR EXIT SQL.SQLCODE
DROP TABLE TABLE_NAME;
With CONTINUE NONE an error is reported, but the script will continue. With EXIT SQL.SQLCODE the script will be terminated in the case of an error.
see also: WHENEVER SQLERROR Docs
One way is to use DBMS_ASSERT.SQL_OBJECT_NAME :
This function verifies that the input parameter string is a qualified SQL identifier of an existing SQL object.
DECLARE
V_OBJECT_NAME VARCHAR2(30);
BEGIN
BEGIN
V_OBJECT_NAME := DBMS_ASSERT.SQL_OBJECT_NAME('tab1');
EXECUTE IMMEDIATE 'DROP TABLE tab1';
EXCEPTION WHEN OTHERS THEN NULL;
END;
END;
/
I have been looking for the same but I ended up writing a procedure to help me out:
CREATE OR REPLACE PROCEDURE DelObject(ObjName varchar2,ObjType varchar2)
IS
v_counter number := 0;
begin
if ObjType = 'TABLE' then
select count(*) into v_counter from user_tables where table_name = upper(ObjName);
if v_counter > 0 then
execute immediate 'drop table ' || ObjName || ' cascade constraints';
end if;
end if;
if ObjType = 'PROCEDURE' then
select count(*) into v_counter from User_Objects where object_type = 'PROCEDURE' and OBJECT_NAME = upper(ObjName);
if v_counter > 0 then
execute immediate 'DROP PROCEDURE ' || ObjName;
end if;
end if;
if ObjType = 'FUNCTION' then
select count(*) into v_counter from User_Objects where object_type = 'FUNCTION' and OBJECT_NAME = upper(ObjName);
if v_counter > 0 then
execute immediate 'DROP FUNCTION ' || ObjName;
end if;
end if;
if ObjType = 'TRIGGER' then
select count(*) into v_counter from User_Triggers where TRIGGER_NAME = upper(ObjName);
if v_counter > 0 then
execute immediate 'DROP TRIGGER ' || ObjName;
end if;
end if;
if ObjType = 'VIEW' then
select count(*) into v_counter from User_Views where VIEW_NAME = upper(ObjName);
if v_counter > 0 then
execute immediate 'DROP VIEW ' || ObjName;
end if;
end if;
if ObjType = 'SEQUENCE' then
select count(*) into v_counter from user_sequences where sequence_name = upper(ObjName);
if v_counter > 0 then
execute immediate 'DROP SEQUENCE ' || ObjName;
end if;
end if;
end;
Hope this helps
And if you want to make it re-enterable and minimize drop/create cycles, you could cache the DDL using dbms_metadata.get_ddl and re-create everything using a construct like this:
declare
v_ddl varchar2(4000);
begin
select dbms_metadata.get_ddl('TABLE','DEPT','SCOTT') into v_ddl from dual;
[COMPARE CACHED DDL AND EXECUTE IF NO MATCH]
exception when others then
if sqlcode = -31603 then
[GET AND EXECUTE CACHED DDL]
else
raise;
end if;
end;
This is just a sample, there should be a loop inside with DDL type, name and owner being variables.
I prefer following economic solution
BEGIN
FOR i IN (SELECT NULL FROM USER_OBJECTS WHERE OBJECT_TYPE = 'TABLE' AND OBJECT_NAME = 'TABLE_NAME') LOOP
EXECUTE IMMEDIATE 'DROP TABLE TABLE_NAME';
END LOOP;
END;
A block like this could be useful to you.
DECLARE
table_exist INT;
BEGIN
SELECT Count(*)
INTO table_exist
FROM dba_tables
WHERE owner = 'SCHEMA_NAME'
AND table_name = 'EMPLOYEE_TABLE';
IF table_exist = 1 THEN
EXECUTE IMMEDIATE 'drop table EMPLOYEE_TABLE';
END IF;
END;
I prefer to specify the table and the schema owner.
Watch out for case sensitivity as well. (see "upper" clause below).
I threw a couple of different objects in to show that is can be used in places besides TABLEs.
.............
declare
v_counter int;
begin
select count(*) into v_counter from dba_users where upper(username)=upper('UserSchema01');
if v_counter > 0 then
execute immediate 'DROP USER UserSchema01 CASCADE';
end if;
end;
/
CREATE USER UserSchema01 IDENTIFIED BY pa$$word
DEFAULT TABLESPACE users
TEMPORARY TABLESPACE temp
QUOTA UNLIMITED ON users;
grant create session to UserSchema01;
And a TABLE example:
declare
v_counter int;
begin
select count(*) into v_counter from all_tables where upper(TABLE_NAME)=upper('ORDERS') and upper(OWNER)=upper('UserSchema01');
if v_counter > 0 then
execute immediate 'DROP TABLE UserSchema01.ORDERS';
end if;
end;
/
Another method is to define an exception and then only catch that exception letting all others propagate.
Declare
eTableDoesNotExist Exception;
PRAGMA EXCEPTION_INIT(eTableDoesNotExist, -942);
Begin
EXECUTE IMMEDIATE ('DROP TABLE myschema.mytable');
Exception
When eTableDoesNotExist Then
DBMS_Output.Put_Line('Table already does not exist.');
End;
just wanted to post a full code that will create a table and drop it if it already exists using Jeffrey's code (kudos to him, not me!).
BEGIN
BEGIN
EXECUTE IMMEDIATE 'DROP TABLE tablename';
EXCEPTION
WHEN OTHERS THEN
IF SQLCODE != -942 THEN
RAISE;
END IF;
END;
EXECUTE IMMEDIATE 'CREATE TABLE tablename AS SELECT * FROM sourcetable WHERE 1=0';
END;
declare
c int;
begin
select count(*) into c from user_tables where table_name = upper('table_name');
if c = 1 then
execute immediate 'drop table table_name';
end if;
end;
That's for checking whether a table in the current schema exists.
For checking whether a given table already exists in a different schema, you'd have to use all_tables instead of user_tables and add the condition all_tables.owner = upper('schema_name')
Source: Stackoverflow.com