如下操作将对已存在的表进行删除，并创建新表，适用于首次初始化过程。
SqlServer：
IF EXISTS (SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = N'tableA')
drop table tableA
go
create table tableA
(
id bigint identity (1, 1) not null primary key,
operator_id bigint not null,
res_source_key numeric(10, 0) not null,
res_source_type int not null
)
go
mysql:
drop table if exists tableA;
create table tableA
(
id bigint(20) not null primary key AUTO_INCREMENT,
operator_id bigint(20) not null,
res_source_key bigint(20) not null,
res_source_type int not null
);
commit;
ORACLE：
Declare
num number;
begin
select count(1) into num from all_tables where table_name = upper('tableA') ;
if num > 0 then
execute immediate 'drop table tableA' ;
end if;
end;
/
create table tableA
(
id number(20) not null primary key,
operator_id number(20) not null,
res_source_key number(20) not null,
res_source_type int not null
);
commit;
++++++++++++++++++++++++++++++++++++++++++++++++++
增加表字段时增加保护：
sqlserver：
If (not exists (select 1 from sysobjects where id in (select id from syscolumns where name = ‘columnA’) and name = ‘tableA’))
begin
alter table tableA add columnA varchar(256) null;
end
go
mysql：
Delimiter //
Create PROCEDURE upgrade()
BEGIN
declare exist_flag int;
select count(0) into exist_flag from INFORMATION_SCHEMA.COLUMNS where TABLE_SCHEMA=‘vnm_db’ and COLUMN_NAME=‘columnA’ and table_name=‘tableA’;
if exist_flag = 0 then
alter table tableA add columnA varchar(256) null;
end if
end;
Call upgrade();
Drop PROCEDURE upgrade;
Commit;
//
Delimiter;
ORACLE：
declare
column_exist_flag int;
BEGIN
select count(0) into column_exist_flag from user_tab_columns where column_name=upper(‘columnA’) and table_name=upper(‘tableA’);
if column_exist_flag = 0 then
execute immediate ‘alter table tableA add columnA varchar(256) null’;
end if
end;
/