[英]Sql subquery for DB2
sql查询需要连接4张表,我这样做了,我必须在其中满足条件的列中显示几列。 说这是Where子句中的查询。 现在,我如何编写子查询来显示另一列(ORG_NAME,在ORG_UNIT中),其内容基于查询中Where子句满足的行。 我写了这段代码,但是对我不起作用:
SELECT T33.CONTRACT_NUM, T135.MINOR_ORG_NUM, T96.ORG_TYPE,T22.CFD_FLAG,
(SELECT T96.ORG_NAME
FROM ORG_UNIT T96, SUB_UNIT T135
WHERE T96.ORG_NUMBER IN (T135.MAJOR_ORG_NUMBER)) AS HEAD_ORG_NAME
FROM
ORG_UNIT T96, SUB_UNIT T135, CUST_CONTRACT T33, CONT_ASSIGNMT T22
WHERE
T96.ORG_NUMBER = T22.ORG_NUMBER
AND T22.CTR_SYS_NUM = T33.CTR_SYS_NUM
AND T96.ORG_NUMBER = T135.MINOR_ORG_NUMBER
AND T135.RELTN_TYPE = 'HOS'
AND T22.CFD_FLAG = 'Y';
作为记录,T135包含总公司编号(MAJOR_ORG_NUMBER)及其子办事处编号(MINOR_ORG_NUMBER)
在SQL中,使用JOIN根据表的公共列将表“合并”在一起。
这是一个简单的指南,可以为您提供基本思路: SQL JOIN
在SQL中,最好总是绘制要执行的操作,因此请参考此链接以查看“ LEFT JOIN”图片示例: LEFT JOIN
使用“ LEFT JOIN”合并表(其中:ORG_UNIT.ORG_NUMBER = SUB_UNIT.MAJOR_ORG_NUMBER),看起来像这样:
LEFT JOIN SUB_UNIT T135 ON T96.ORG_NUMBER = T135.MAJOR_ORG_NUMBER
在查询中,在“ FROM”之后和“ WHERE”之前放置一个JOIN:
SELECT
T33.CONTRACT_NUM,
T135.MINOR_ORG_NUM,
T96.ORG_TYPE,
T22.CFD_FLAG,
T135.ORG_NAME AS HEAD_ORG_NAME
FROM
ORG_UNIT T96,
CUST_CONTRACT T33,
CONT_ASSIGNMT T22
LEFT JOIN SUB_UNIT T135 ON T96.ORG_NUMBER = T135.MAJOR_ORG_NUMBER
WHERE
T96.ORG_NUMBER = T22.ORG_NUMBER
AND T22.CTR_SYS_NUM = T33.CTR_SYS_NUM
AND T96.ORG_NUMBER = T135.MINOR_ORG_NUMBER
AND T135.RELTN_TYPE = 'HOS'
AND T22.CFD_FLAG = 'Y';
请注意,您可以(应该)使用JOIN合并所有表(并避免使用昂贵的WHERE条件):
SELECT
T33.CONTRACT_NUM,
T135.MINOR_ORG_NUM,
T96.ORG_TYPE,
T22.CFD_FLAG,
T135.ORG_NAME AS HEAD_ORG_NAME
FROM
ORG_UNIT T96
LEFT JOIN SUB_UNIT T135 ON
T96.ORG_NUMBER = T135.MAJOR_ORG_NUMBER
AND T96.ORG_NUMBER = T135.MINOR_ORG_NUMBER
LEFT JOIN ON
CONT_ASSIGNMT T22 ON T96.ORG_NUMBER = T22.ORG_NUMBER
LEFT JOIN ON
CUST_CONTRACT T33 ON T22.CTR_SYS_NUM = T33.CTR_SYS_NUM
WHERE
T135.RELTN_TYPE = 'HOS'
AND T22.CFD_FLAG = 'Y';
有几种JOIN类型(左/右/内/外),因此请使用所需的一种。
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