oracle正确缩短字段（要考虑以前的是否有值）

--表名.email (字段调整为varchar2(100))
--表名.corpname (字段调整为varchar2(40))
--表名.INDUSTRY (字段调整为varchar2(2))
--表名.duty (字段调整为varchar2(32))
declare
iCount INTEGER := 0;
begin
select count(1) into iCount from user_tab_cols u where lower(u.table_name )= '表名' and u.column_name = 'email';
if iCount > 0 THEN
UPDATE 表名 t SET t.email = substrb(t.email, 0, 100) WHERE lengthb(t.email)>100;
COMMIT;
execute immediate 'alter table 表名 modify email varchar2(100)';--原值---120
END IF;
select count(1) into iCount from user_tab_cols u where lower(u.table_name )= '表名' and u.column_name = 'corpname';
if iCount > 0 THEN
UPDATE 表名 t SET t.corpname = substrb(t.corpname, 0, 40) WHERE lengthb(t.corpname)>40;
COMMIT;
execute immediate 'alter table 表名 modify corpname varchar2(40)';--原值---80
END IF;
select count(1) into iCount from user_tab_cols u where lower(u.table_name )= '表名' and u.column_name = 'INDUSTRY';
if iCount > 0 THEN
UPDATE 表名 t SET t.INDUSTRY=trim(t.INDUSTRY) where lengthb(INDUSTRY)>2;
COMMIT;
execute immediate 'alter table 表名 modify INDUSTRY varchar2(2)';--原值是字典值---3
END IF;
select count(1) into iCount from user_tab_cols u where lower(u.table_name )= '表名' and u.column_name = 'duty';
if iCount > 0 THEN
execute immediate 'alter table 表名 modify duty varchar2(32)';--原值----60
END IF;
END;
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