oracle将select作为字段查询

在Oracle中，如果你想将一个SELECT语句作为字段的值，你可以使用子查询或者使用WITH子句（也称为公用表表达式CTE）。以下是两种方法的示例：

方法1：使用子查询

语法如下：

SELECT
    column1,
    (SELECT COUNT(*) FROM another_table WHERE another_table.column2 = table1.column1) AS count_value
FROM
    table1;
  

实例：

SELECT
(SELECT a.companycname
          FROM ggcompany a
         WHERE a.companycode = SUBSTR(mm.companycode, 0, 4)) 二级机构,
       (SELECT a.companycname
          FROM ggcompany a
         WHERE a.companycode = SUBSTR(mm.companycode, 0, 6)) 三级机构,
       (SELECT a.companycname
       
          FROM ggcompany a
         WHERE a.companycode = mm.companycode) 四级机构,
       mm.policyno 保单号
       from gppolicyplandetail mm

方法2：使用WITH子句（CTE）

语法：

WITH count_cte AS (
    SELECT column2, COUNT(*) AS count_value
    FROM another_table
    GROUP BY column2
)
SELECT
    t1.column1,
    count_cte.count_value
FROM
    table1 t1
    LEFT JOIN count_cte ON count_cte.column2 = t1.column1;

解释：count_cte 是中间表，命名随意，要是需要多个中间表，可以用逗号连接。

实例：

WITH
          w AS (
                    SELECT
                              statdate          ,
                              classname         ,
                              riskname          ,
                              cityname          ,
                              policyno          ,
                              registno          ,
                              claimno           ,
                              damagedate        ,
                              reportdate        ,
                              claimdate         ,
                              underwriteenddate ,
                              endcasedate       ,
                              rgstcncldate      ,
                              canceldate        ,
                              firstestloss      ,
                              unsettledpaidbegin,
                              unsettledpaidend  ,
                              settled           ,
                              sumpaid           ,
                              reportlossfee     ,
                              canceldateloss
                    FROM
                              r_lsts_jsreportlist
                    WHERE
                              statdate = DATE '2022-03-31'
          )     ,
          ff AS (
                    SELECT
                              statdate          ,
                              classname         ,
                              riskname          ,
                              cityname          ,
                              policyno          ,
                              registno          ,
                              claimno           ,
                              damagedate        ,
                              reportdate        ,
                              claimdate         ,
                              underwriteenddate ,
                              endcasedate       ,
                              rgstcncldate      ,
                              canceldate        ,
                              firstestloss      ,
                              unsettledpaidbegin,
                              unsettledpaidend  ,
                              settled           ,
                              sumpaid           ,
                              reportlossfee     ,
                              canceldateloss
                    FROM
                              r_lsts_jsreportlist
                    WHERE
                              statdate = DATE '2024-09-30'
          )
SELECT
          ff.statdate 统计日期,
          ff.classname 险类 ,
          ff.riskname 险种  ,
          ff.cityname 机构  ,
          w.settled
FROM
          ff
          LEFT JOIN w ON ff.riskname = w.riskname AND
          ff.policyno = w.policyno AND
          ff.registno = w.registno AND
          ff.claimno = w.claimno

         解释：W和FF都是临时表，中间用逗号隔开，中间结束需要有select ，select前不能有逗号。