Drop table if it exists with DB2/400 SQL - sql

Question

My goal is pretty straightforward - if table has rows, drop it.
Despite the fact that currently there are several similar answers none of them worked for me.
DB2 Drop table if exists equivalent
Suggested solution:
IF EXISTS (SELECT name FROM sysibm.systables WHERE name = 'mylib.mytable') THEN
DROP TABLE mylib.mytable;END IF;
Result:
SQL State: 42601 Vendor Code: -199 Message: [SQL0199] Keyword IF not expected.
Valid tokens: ( CL END GET SET CALL DROP FREE HOLD LOCK OPEN WITH ALTER BEGIN
Drop DB2 table if exists
Suggested solution:
--#SET TERMINATOR #
begin
declare statement varchar(128);
declare continue handle for sqlstate '42710' BEGIN END;
SET STATEMENT = 'DROP TABLE MYLIB.MYTABLE';
EXECUTE IMMEDIATE STATEMENT;
end #
Result:
Message: [SQL0104] Token HANDLE was not invalid. Valid tokens: HANDLER or, if replace handle with handler:
Message: [SQL0199] Keyword STATEMENT not expected. Valid tokens: SQL PATH RESULT SCHEMA CURRENT CONNECTION DESCRIPTOR.
From answer about views
Suggested solution:
DROP TABLE MY_TABLE ONLY IF EXISTS source.
Result:
Message: [SQL0104] Token ONLY was not invalid. Valid tokens: RESTRICT CASCADE
So, I wonder if an alternate solution exists. CL solution is also interesting.

Answer 1

I'm assuming you may want to do this more than once, so a procedure might be in order.
CREATE or replace PROCEDURE DROP_LIVE_TABLE
(in #table varchar(10)
,in #library varchar(10)
)
BEGIN
declare #stmt varchar(100);
declare #cnt int;
IF exists( select * from systables
where sys_dname = #library
and sys_tname = #table
and table_type in ('P','T')
) THEN
SELECT int(sum(number_rows))
INTO #cnt
from SYSTABLESTAT
where sys_dname = #library
and sys_tname = #table
;
IF #cnt > 0 THEN
set #stmt = 'DROP TABLE '||#library||'.'||#table||' CASCADE';
execute immediate #stmt;
END IF;
END IF;
RETURN;
END;
The CASCADE keyword causes any dependent objects such as indexes, logical files, views, or such to be deleted as well.

Answer 2

Here is a CL answer to this question:
PGM PARM(&FILENAME)
DCL VAR(&FILENAME) TYPE(*CHAR) LEN(10)
DCL VAR(&NUMRECS) TYPE(*DEC) LEN(10 0)
RTVMBRD FILE(&FILENAME) NBRCURRCD(&NUMRECS)
IF COND(&NUMRECS > 0) THEN(DLTF +
FILE(&FILENAME))
OUT: ENDPGM
This solution would have trouble if the physical file has dependencies such as indexes or logical files. Those dependencies would have to be deleted first.
The solution by #danny117 on the other hand does not work in all environments. For example I was unable to coerce it to work in SQuirreL client. But it does work in i Navigator. It also works in RUNSQLSTM, but I was unable to determine how to make it work with unqualified table references. If the tables are unqualified, RUNSQLSTM uses the default collection from DFTRDBCOL. The CURRENT_SCHEMA special register does not return the value from DFTRDBCOL.
Here is the if table has rows drop it solution using a compound statement:
begin
if( exists(
select 1 from qsys2.systables
where table_schema = 'MYLIB'
and table_name = 'MYTABLE'
)) then
if( exists(
select 1 from mylib.mytable
)) then
drop table mylib.mytable;
end if;
end if;
end;
I am guessing at the reason you would want to do this, but if it is to allow creation of a new table, then best way may be with a CREATE OR REPLACE TABLE if you are at IBM i v7.2 or greater.
If all you want to do is make sure you have an empty table, TRUNCATE (v7.2+) or DELETE may be better options.

Answer 3

Drop table if exists using atomic statement.
BEGIN ATOMIC
IF( EXISTS(
SELECT 1 FROM TABLES
WHERE TABLE_SCHEMA = 'MYLIB'
AND TABLE_NAME = 'MYTABLE'
)) THEN
DROP TABLE MYLIB/MYTABLE;
END IF;
END;

Answer 4

try this:
BEGIN
IF EXISTS (SELECT NAME FROM QSYS2.SYSTABLES WHERE TABLE_SCHEMA = 'YOURLIBINUPPER' AND TABLE_NAME = 'YOURTABLEINUPPER') THEN
DROP TABLE YOURLIB.YOURTABLE;
END IF;
END ;