主 select 查询以及具有 "select * dual" 的子查询

Question

我有以下查询，它有一个从 dual 到 select 的子查询。主查询和子查询的结果都需要在输出中显示。

SELECT
a.ROW_EXISTS AS CLIENT_EXIST,
c.AP_Before AS AP_before,
c.AP_TIMESTAMP AS AP_TIMESTAMP,
cd.AAM_FLAG AS AAM_FLAG,
cd.SSM_FLAG AS SSM_FLAG
FROM 
(
select
case when exist (select 1 from c.clients where client_id='c-001' then 'Y' else 'N' end as ROW_EXISTS
from dual
) AS a
INNER JOIN CLIENT_DYN cd ON c.CLIENT_ID = cd.CLIENT_ID
WHERE c.CLIENT_ID = 'c-001';

执行查询时，错误 ORA-00933: SQL command not properly ended 在行 ) AS A 附近遇到。

Answer 1

exists，不是exist
缺少右子查询括号
table 别名不接受 as 关键字（相对于列）

SELECT a.ROW_EXISTS AS CLIENT_EXIST,
       c.AP_Before AS AP_before,
       c.AP_TIMESTAMP AS AP_TIMESTAMP,
       cd.AAM_FLAG AS AAM_FLAG,
       cd.SSM_FLAG AS SSM_FLAG
  FROM client c
       INNER JOIN CLIENT_DYN cd ON c.CLIENT_ID = cd.CLIENT_ID
       CROSS JOIN (SELECT CASE
                             WHEN EXISTS
                                     (SELECT 1
                                        FROM clients c
                                       WHERE client_id = 'c-001')
                             THEN
                                'Y'
                             ELSE
                                'N'
                          END AS ROW_EXISTS
                     FROM DUAL) a
 WHERE c.CLIENT_ID = 'c-001';

Answer 2

修复语法错误后（EXISTS 而不是 EXIST，缺少右大括号并且不对 table 别名使用 AS 关键字），您的外部查询是

SELECT <some columns>
FROM   (SELECT 'Y/N Value' AS row_exists FROM DUAL) a
       INNER JOIN client_dyn cd
       ON (c.CLIENT_ID = cd.CLIENT_ID)

外部查询中没有 c table 或别名，因为子查询的别名是 a 而不是 c 并且只有子查询包含一个 row_exists 列而不是 CLIENT_ID 列；所以在这两点上，c.CLIENT_ID 都是无效的。

您可能想要的是：

如果要检查 client_id 匹配当前行：

SELECT CASE WHEN c.client_id IS NOT NULL THEN 'Y' ELSE 'N' END AS CLIENT_EXIST,
       c.AP_Before AS AP_before,
       c.AP_TIMESTAMP AS AP_TIMESTAMP,
       cd.AAM_FLAG AS AAM_FLAG,
       cd.SSM_FLAG AS SSM_FLAG
FROM   clients c
       RIGHT OUTER JOIN CLIENT_DYN cd
       ON (c.CLIENT_ID = 'c-001' AND c.CLIENT_ID = cd.CLIENT_ID);

或者，如果您想检查 client_id 是否与返回的行集合匹配：

SELECT CASE
       WHEN COUNT(CASE WHEN c.client_id = 'c-001' THEN 1 END) OVER () > 0
       THEN 'Y'
       ELSE 'N'
       END AS CLIENT_EXIST,
       c.AP_Before AS AP_before,
       c.AP_TIMESTAMP AS AP_TIMESTAMP,
       cd.AAM_FLAG AS AAM_FLAG,
       cd.SSM_FLAG AS SSM_FLAG
FROM   clients c
       INNER JOIN CLIENT_DYN cd
       ON (c.CLIENT_ID = cd.CLIENT_ID);

或者，如果您想检查 client_id 是否存在于 clients table 中的任何位置：

SELECT CASE
       WHEN EXISTS(SELECT 1 FROM clients WHERE client_id = 'c-001')
       THEN 'Y'
       ELSE 'N'
       END AS CLIENT_EXIST,
       c.AP_Before AS AP_before,
       c.AP_TIMESTAMP AS AP_TIMESTAMP,
       cd.AAM_FLAG AS AAM_FLAG,
       cd.SSM_FLAG AS SSM_FLAG
FROM   clients c
       INNER JOIN CLIENT_DYN cd
       ON (c.CLIENT_ID = cd.CLIENT_ID);

取决于您要如何检查客户端是否存在。

主 select 查询以及具有 "select * dual" 的子查询

Main select query together with subquery having "select * dual"

oracle

subquery

case

dual-table