Oracle中Union与Union All的区别(适用多个数据库)

如果我们需要将两个select语句的结果作为一个整体显示出来，我们就需要用到union或者union all关键字。union(或称为联合)的作用是将多个结果合并在一起显示出来

Union 与 Union ALL 的作用都是合并 SELECT 的查询结果集，那么它们有什么不同呢？

Union 将查询到的结果集合并后进行重查，将其中相同的行去除。缺点：效率低；
而Union ALL 则只是合并查询的结果集，并不重新查询，效率高，但是可能会出现冗余数据。

Union：对两个结果集进行并集操作，不包括重复行，同时进行默认规则的排序；

Union All：对两个结果集进行并集操作，包括重复行，不进行排序；

Intersect：对两个结果集进行交集操作，不包括重复行，同时进行默认规则的排序；

Minus：对两个结果集进行差操作，不包括重复行，同时进行默认规则的排序。

可以在最后一个结果集中指定Order by子句改变排序方式。

例如：

复制代码代码如下:

select employee_id,job_id from employees
union
select employee_id,job_id from job_history

以上将两个表的结果联合在一起。这两个例子会将两个select语句的结果中的重复值进行压缩，也就是结果的数据并不是两条结果的条数的和。如果希望即使重复的结果显示出来可以使用union all,例如：

2.在oracle的scott用户中有表emp

复制代码代码如下:

select * from emp where deptno >= 20
union all
select * from emp where deptno <= 30

这里的结果就有很多重复值了。

有关union和union all关键字需要注意的问题是：

union 和 union all都可以将多个结果集合并，而不仅仅是两个，你可以将多个结果集串起来。
使用union和union all必须保证各个select 集合的结果有相同个数的列，并且每个列的类型是一样的。但列名则不一定需要相同，oracle会将第一个结果的列名作为结果集的列名。例如下面是一个例子：

代码如下:
select empno,ename from emp
union
select deptno,dname from dept

我们没有必要在每一个select结果集中使用order by子句来进行排序，我们可以在最后使用一条order by来对整个结果进行排序。例如：

复制代码代码如下:

select empno,ename from emp
union
select deptno,dname from dept
order by ename;

转自：http://www.jb51.net/article/30792.htm

本人写的，比较复杂一点的sql（left join union all）

-- 查询基本信息
select * from
(
select
max(trans_item.BASIC_TERM_ID) BASIC_TERM_ID,
trans_item.APP_TERM_NO APP_TERM_NO,
max(trans_item.DEVICE_TYPE) DEVICE_TYPE,
max(trans_item.MODEL_DESC) MODEL_DESC,
max(trans_item.branch_name) branch_name,
max(trans_item.sub_name) sub_name,
max(trans_item.self_name) self_name,
max(trans_item.INST_TYPE) INST_TYPE
from(
select    term.TERMINAL_ID BASIC_TERM_ID,
term.APP_TERM_NO APP_TERM_NO,
device.DEVICE_TYPE DEVICE_TYPE,
model.MODEL_DESC MODEL_DESC,
branch.SHORT_NAME branch_name,
subbranch.SHORT_NAME sub_name,
self.SHORT_NAME self_name,
self.INST_TYPE INST_TYPE
from SELFCUR.OPS_TERMINAL_INFO    term,
SELFCUR.OPS_DEVICE_INFO     device,
SELFCUR.OPS_DEVICE_MODEL    model,
SELFCUR.OPS_INSTITUTION     branch,
SELFCUR.OPS_INSTITUTION     subbranch,
SELFCUR.OPS_INSTITUTION     self,
SELFCUR.BIZ_MAIN_TRANS    trans
where    trans.TERM_ID=term.APP_TERM_NO
and term.TERMINAL_ID=device.TERMINAL_ID
and device.MODEL_ID=model.MODEL_ID
and term.INST_ID=self.INST_ID
and self.PARENT_INST_ID=subbranch.INST_ID
and subbranch.PARENT_INST_ID=branch.INST_ID
-- 这里需要加入特殊符号来标识，用界面传过来的参数组成sql进行替换
--XXXXYYYY--
union all
select    term.TERMINAL_ID BASIC_TERM_ID,
term.APP_TERM_NO APP_TERM_NO,
device.DEVICE_TYPE DEVICE_TYPE,
model.MODEL_DESC MODEL_DESC,
branch.SHORT_NAME branch_name,
subbranch.SHORT_NAME sub_name,
self.SHORT_NAME self_name,
self.INST_TYPE INST_TYPE
from SELFCUR.OPS_TERMINAL_INFO    term,
SELFCUR.OPS_DEVICE_INFO     device,
SELFCUR.OPS_DEVICE_MODEL    model,
SELFCUR.OPS_INSTITUTION     branch,
SELFCUR.OPS_INSTITUTION     subbranch,
SELFCUR.OPS_INSTITUTION     self,
SELFCUR.BIZ_MAIN_TRANS_HIS    trans_his
where    trans_his.TERM_ID=term.APP_TERM_NO
and term.TERMINAL_ID=device.TERMINAL_ID
and device.MODEL_ID=model.MODEL_ID
and term.INST_ID=self.INST_ID
and self.PARENT_INST_ID=subbranch.INST_ID
and subbranch.PARENT_INST_ID=branch.INST_ID
-- 这里需要加入特殊符号来标识，用界面传过来的参数组成sql进行替换
--XXXXYYYY--
)trans_item
group by trans_item.APP_TERM_NO
)trans_basic
left join(
-- 联通缴费
select
trans_pay_lt.TERM_ID TERM_ID,
) PAY_LT_Count,
sum(trans_pay_lt.TRAN_AMT) PAY_LT_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
'
) trans_pay_lt
group by trans_pay_lt.TERM_ID
)trans_pay_lt_l
on
trans_basic.APP_TERM_NO=trans_pay_lt_l.TERM_ID
left join(
-- 移动缴费
select
trans_pay_yd.TERM_ID TERM_ID,
) PAY_YD_Count,
sum(trans_pay_yd.TRAN_AMT) PAY_YD_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
'
) trans_pay_yd
group by trans_pay_yd.TERM_ID
)trans_pay_yd_l
on
trans_basic.APP_TERM_NO=trans_pay_yd_l.TERM_ID
left join(
-- 查询电信缴费
select
trans_pay_dx.TERM_ID TERM_ID,
) PAY_DX_Count,
sum(trans_pay_dx.TRAN_AMT) PAY_DX_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
'
) trans_pay_dx
group by trans_pay_dx.TERM_ID
)trans_pay_dx_l
on
trans_basic.APP_TERM_NO=trans_pay_dx_l.TERM_ID
left join(
-- 电力缴费
select
trans_pay_dl.TERM_ID TERM_ID,
) PAY_DL_Count,
sum(trans_pay_dl.TRAN_AMT) PAY_DL_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
--重庆电力014 三峡电力 008
')
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
--重庆电力014 三峡电力 008
')
) trans_pay_dl
group by trans_pay_dl.TERM_ID
)trans_pay_dl_l
on
trans_basic.APP_TERM_NO=trans_pay_dl_l.TERM_ID
left join(
-- 自来水缴费
select
trans_pay_zls.TERM_ID TERM_ID,
) PAY_ZLS_Count,
sum(trans_pay_zls.TRAN_AMT) PAY_ZLS_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
--水务2测试 004 水费 005
')
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
--水务2测试 004 水费 005
')
) trans_pay_zls
group by trans_pay_zls.TERM_ID
)trans_pay_zls_l
on
trans_basic.APP_TERM_NO=trans_pay_zls_l.TERM_ID
left join(
-- 燃气缴费
select
trans_pay_rq.TERM_ID TERM_ID,
) PAY_RQ_Count,
sum(trans_pay_rq.TRAN_AMT) PAY_RQ_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
--再生资源 003
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
--再生资源 003
'
) trans_pay_rq
group by trans_pay_rq.TERM_ID
)trans_pay_rq_l
on
trans_basic.APP_TERM_NO=trans_pay_rq_l.TERM_ID
left join(
-- 现金交易 取款
select
trans_cash_qk.TERM_ID TERM_ID,
) CASH_QK_Count,
sum(trans_cash_qk.TRAN_AMT) CASH_QK_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
) trans_cash_qk
group by trans_cash_qk.TERM_ID
)trans_cash_qk_l
on
trans_basic.APP_TERM_NO=trans_cash_qk_l.TERM_ID
left join(
-- 现金交易 存款
select
trans_cash_ck.TERM_ID TERM_ID,
) CASH_CK_Count,
sum(trans_cash_ck.TRAN_AMT) CASH_CK_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
) trans_cash_ck
group by trans_cash_ck.TERM_ID
)trans_cash_ck_l
on
trans_basic.APP_TERM_NO=trans_cash_ck_l.TERM_ID
left join(
-- 现金交易 查询
--余额查询1011001 查询交易明细1011002 积分查询 1011003
select
trans_cash_cx.TERM_ID TERM_ID,
) CASH_CX_Count
from(
select trans.TERM_ID TERM_ID
from SELFCUR.BIZ_MAIN_TRANS trans
'
union all
select trans_his.TERM_ID TERM_ID
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
) trans_cash_cx
group by trans_cash_cx.TERM_ID
)trans_cash_cx_l
on
trans_basic.APP_TERM_NO=trans_cash_cx_l.TERM_ID
left join(
-- 现金交易 转账
select
trans_cash_zh.TERM_ID TERM_ID,
) CASH_ZH_Count,
sum(trans_cash_zh.TRAN_AMT) CASH_ZH_Money
from(
select trans.TERM_ID TERM_ID,
trans.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS trans
'
union all
select trans_his.TERM_ID TERM_ID,
trans_his.TRAN_AMT TRAN_AMT
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
) trans_cash_zh
group by trans_cash_zh.TERM_ID
) trans_cash_zh_l
on
trans_basic.APP_TERM_NO=trans_cash_zh_l.TERM_ID
left join(
-- 补登折 存折
select
trans_budeng_cz.TERM_ID TERM_ID,
) BUDENG_CZ_Count
from(
select trans.TERM_ID TERM_ID
from SELFCUR.BIZ_MAIN_TRANS trans
'
union all
select trans_his.TERM_ID TERM_ID
from SELFCUR.BIZ_MAIN_TRANS_HIS trans_his
'
) trans_budeng_cz
group by trans_budeng_cz.TERM_ID
) trans_budeng_cz_l
on
trans_basic.APP_TERM_NO=trans_budeng_cz_l.TERM_ID

巴特西

Oracle中Union与Union All的区别(适用多个数据库)

Oracle中Union与Union All的区别(适用多个数据库)

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