oracle 查询判断语句

1.查询表是否存在，如果不存在，就添加

select count(*)
into v_count
from user_all_tables
where table_name = 'A';
if v_count = 0 then
execute immediate 'create table A(ID NUMBER not null';
end If;

2.查询表的主键是否存在，不存在就添加主键

select count(*)
into v_count
from user_cons_columns a
where a.constraint_name = 'PK_A'
and a.table_name = 'A;
if v_count = 0 then
execute immediate 'alter table A
add constraint PK_A primary key (ID)
using index
tablespace DAAN_DATA
pctfree 10
initrans 2
maxtrans 255
storage
(
initial 64K
minextents 1
maxextents unlimited
)';
end if;

3.查询表的序列是否存在，不存在的话，添加

select count(*)
into v_count
from user_sequences
where sequence_name = 'SEQ_A_ID';
if v_count = 0 then
execute immediate 'create sequence SEQ_A_ID
minvalue 1 maxvalue 9999999999999999 start with 61 increment by 1 cache 20';
end if;

4.判断表是否存在该字段，不存在的话，就添加

select COUNT(*)
into v_count
from user_tab_columns
where table_name = 'A'
and column_name = 'CREATE_TIME';
if v_count = 0 then
execute immediate 'alter table A add(CREATE_TIME DATE default SYSDATE not null)';
end if;

5.判断表是否存在该条数据，如果不存在，就添加，存在，就修改

merge into A a
using (select count(*) num from A where id = 1) c
on (c.num <> 0)

WHEN MATCHED THEN

update set a.id=2 where a.id=1
WHEN not MATCHED THEN
insert
(id)
values
(1);
commit;