Cursor and dynamic SQL statement

Hi all,

I am new to DB2 and writing a DB2 script to change all INT data type in my database to BIGINT. In SQL Server I can do something as below. But when I ran it on DB2 Command Editor, it always said "DB21034E The command was processed as an SQL statement because it was not a
valid Command Line Processor command..."

Does anyone know how to change this script to make it work under DB2?

Thanks!!
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BEGIN

DECLARE tablename VARCHAR(100)
DECLARE columnname VARCHAR(100)
DECLARE sqlstmt VARCHAR(1000)
DECLARE flag bigint
declare int_cursor cursor with hold for SELECT t.tabname, c.colname FROM syscat.columns c JOIN syscat.tables t ON c.tabname = t.tabname WHERE c.typename = 'INTEGER' AND t.tabschema= 'my'

OPEN int_cursor
repeat
FETCH int_cursor INTO tablename, columnname

SET sqlstmt ='ALTER TABLE my.' + tablename + ' ALTER COLUMN ' + columnname + ' SET DATA TYPE BIGINT'
EXEC sqlstmt

until exitcode=1
END repeat
CLOSE int_cursor

END