深入理解和使用Oracle中with as语句以及与增删改查的结合使用

WITH AS短语,也叫做子查询部分(subquery factoring),可以做很多事情,定义一个SQL片断,该SQL片断会被整个SQL语句所用到。有的时候,是为了让SQL语句的可读性更高些,也有可能是在UNION ALL的不同部分,作为提供数据的部分。
特别对于UNION ALL比较有用。因为UNION ALL的每个部分可能相同,但是如果每个部分都去执行一遍的话,则成本太高,所以可以使用WITH AS短语,则只要执行一遍即可。如果WITH AS短语所定义的表名被调用两次以上,则优化器会自动将WITH AS短语所获取的数据放入一个TEMP表里,如果只是被调用一次,则不会。而提示materialize则是强制将WITH AS短语里的数据放入一个全局临时表里。

一、with as 语法
单个语法:
with  tempName  as  ( select  ....)
select  ...

多个语法:
with  tempName1  as  ( select  ....),
tempName2  as  ( select  ....),
tempName3  as  ( select  ....) ...
select  ...  

With查询语句不是以select开始的,而是以“WITH”关键字开头
可认为在真正进行查询之前预先构造了一个临时表TT,之后便可多次使用它做进一步的分析和处理

二、WITH AS实例
例:现在要从1-19中得到11-14。一般的sql如下:
select   *   from
(
             --模拟生一个20行的数据
              SELECT   LEVEL   AS  lv
                FROM  DUAL
         CONNECT  BY   LEVEL   <   20
) tt
  WHERE  tt.lv  >   10   AND  tt.lv  <   15
 
使用With as 的SQL为:
with TT as ( --模拟生一个20行的数据 SELECT LEVEL AS lv FROM DUAL CONNECT BY LEVEL < 20 ) select lv from TT WHERE lv > 10 AND lv < 15

多个临时表实例:
WITH
T3 AS
(
SELECT T1.ID, T1.CODE1, T2.DESCRIPTION
FROM TB_DATA T1, TB_CODE T2
WHERE T1.CODE1 = T2.CODE
),
T4 AS
(
SELECT T1.ID, T1.CODE2, T2.DESCRIPTION
FROM TB_DATA T1, TB_CODE T2
WHERE T1.CODE2 = T2.CODE
)
SELECT T3.ID, T3.DESCRIPTION, T4.DESCRIPTION
FROM T3, T4
WHERE T3.ID = T4.ID
ORDER BY ID;  

三、WITH Clause方法的优点
     增加了SQL的易读性,如果构造了多个子查询,结构会更清晰;更重要的是:“一次分析,多次使用”,这也是为什么会提供性能的地方,达到了“少读”的目标。
     第一种使用子查询的方法表被扫描了两次,而使用WITH Clause方法,表仅被扫描一次。这样可以大大的提高数据分析和查询的效率。
     另外,观察WITH Clause方法执行计划,其中“SYS_TEMP_XXXX”便是在运行过程中构造的中间统计结果临时表。

四、WITH AS 与增删改查结合用法
注意:1. with必须紧跟引用的select语句
2.with创建的临时表必须被引用,否则报错
4.1与select查询语句结合使用
查询同一个单据编号对应的借款单和核销单中,借款金额不相等的单据
with verificationInfo as
 (select ment.fnumber,
         sum(t.famount) vLoanSum,
         ment.fnumber "单据编号",
         sum(t.famount) "核销单中借款总额"
    from shenzhenjm.t_finance_expenseremburseitem t
    left join shenzhenjm.t_finance_expenserembursement ment
      on ment.fid = t.fkrembursementid
   where 1 = 1
   group by ment.fnumber),

loanInfo as
 (select ment.fnumber,
         sum(t.famount) loanSum,
         ment.fnumber "单据编号",
         sum(t.famount) "借款单中借款总额"
    from shenzhenjm.t_finance_expenseremburseitem2 t
    left join shenzhenjm.t_finance_expenserembursement ment
      on ment.fid = t.fkrembursementid
   where 1 = 1
   group by ment.fnumber)

select *
  from verificationInfo v, loanInfo l
 where l.fnumber = v.fnumber
   and l.loanSum != v.vLoanSum;
4.2与insert结合使用
如下的with as语句,不能放在insert前,而是放在紧接着要调用的地方前
要求将同一个单据编号对应的借款单和核销单中,借款金额不相等的单据,对应的借款单删除,并将对应的核销单插入到借款单表中 (借款单和核销单表结构完全一样)
insert into T_finance_ExpenseRemburseItem2
  (FID,
   FKREMBURSEMENTID,
   FAMOUNT,
   FKCREATEBYID,
   FCREATETIME,
   FKCUID,
   FKCOSTTYPEID,
   FCOSTTYPENAME)

  with verificationInfo as
   (select ment.fnumber,
           sum(t.famount) vLoanSum,
           ment.fnumber "单据编号",
           sum(t.famount) "核销单中借款总额"
      from shenzhenjm.t_finance_expenseremburseitem t
      left join shenzhenjm.t_finance_expenserembursement ment
        on ment.fid = t.fkrembursementid
     where 1 = 1
     group by ment.fnumber),
  
  loanInfo as
   (select ment.fnumber,
           sum(t.famount) loanSum,
           ment.fnumber "单据编号",
           sum(t.famount) "借款单中借款总额"
      from shenzhenjm.t_finance_expenseremburseitem2 t
      left join shenzhenjm.t_finance_expenserembursement ment
        on ment.fid = t.fkrembursementid
     where 1 = 1
     group by ment.fnumber)
  
  select sys_guid(),
         ment.fid,
         t.famount,
         ment.fkcreatebyid,
         ment.fcreatetime,
         ment.fkcuid,
         t.fkcosttypeid,
         t.fcosttypename
    from T_finance_ExpenseRemburseItem t
    left join t_finance_expenserembursement ment
      on ment.fid = t.fkrembursementid
   where 1 = 1
     and exists (select *
            from verificationInfo v, loanInfo l
           where l.fnumber = v.fnumber
             and l.loanSum != v.vLoanSum
             and v.fnumber = ment.fnumber);
4.3 与delete删除结合使用
delete from t_finance_expenseremburseitem2 item2
 where exists(with temp as (select t.fnumber,
                             sum(item1.famount) vloanSum,
                             sum(item1.frealityamount) vSum,
                             sum(item2.famount) loanSum
                        from t_finance_expenserembursement t
                        left join t_finance_expenseremburseitem item1
                          on item1.fkrembursementid = t.fid
                        left join t_finance_expenseremburseitem2 item2
                          on item2.fkrembursementid = t.fid
                       where 1 = 1
                         and t.frembursementtype = 'LOAN_REPORT'
                         and to_char(t.fcreatetime, 'yyyy') > '2017'
                       group by t.fnumber
                       order by t.fnumber asc)
 
   select 1
     from temp t
     left join t_finance_expenserembursement ment
       on t.fnumber = ment.fnumber
     left join t_finance_expenseremburseitem2 item
       on item.fkrembursementid = ment.fid
    where t.vloanSum != t.loanSum
      and item.fid = item2.fid);


4.4与update结合使用
update dest b
   set b.NAME =
       (with t as (select * from temp)
         select a.NAME from temp a where a.ID = b.ID)


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