仅当特定列的值为 1 时才考虑内部联接，如果该特定列的值为 2 则不考虑联接

Question

如果特定列的值为 1，则强制考虑内部连接子查询，否则如果列值为 2，则甚至不考虑内部连接。如果特定列的值为 1，则强制考虑内部连接子查询，否则如果其值为 2，则不考虑内部连接。

SELECT DISTINCT Ta.aFI, Ta.cid, Ta.applicationno, dbk.bsg, dbk.cis, Ta.time
FROM   ArrowAged Ta
INNER JOIN infy sc WITH (NOLOCK) ON sc.id = Ta.applicationno
INNER JOIN Intelligent ING WITH (NOLOCK) ON sc.serverid = ING.serverid AND sc.typeid = ING.typeid 
LEFT JOIN IntelligentProp IP WITH (NOLOCK) ON ING.id = IP.cnid AND IP.attrName = 'sc table' AND IP.changed = 0
INNER JOIN DBKnowledge dbk WITH (NOLOCK) ON dbk.bSID  = sc.bS AND ((ISNULL(IP.value, 0) = 0) OR dbk.databasename = sc.uniqueID)
INNER JOIN (SELECT DISTINCT applicationno FROM impObjects WITH (NOLOCK) WHERE objectType in (2,6) and name = 'Version1' and checksumid = CHECKSUM(N'Version1')) AF  ON AF.applicationno = Ta.applicationno

现在在查询中看到有这个语句

INNER JOIN (SELECT DISTINCT applicationno FROM impObjects WITH (NOLOCK) WHERE objectType in (2,6) and name = 'Version1' and checksumid = CHECKSUM(N'Version1')) AF  ON AF.applicationno = Ta.applicationno

where 如果etype 为1 则强制考虑inner join 和里面的子查询条件，否则不考虑inner join 语句。 etype 1 必须跟在子查询、内连接和条件之后。

例如：

case dbk.etype = 1
INNER JOIN (SELECT DISTINCT applicationno FROM impObjects WITH (NOLOCK) WHERE objectType in (2,6) and name = 'Version1' and checksumid = CHECKSUM(N'Version1')) AF  ON AF.applicationno = Ta.applicationno
case dbk.etype = 2
DON'T CONSIDER THE INNER JOIN STATEMENT

注意：我不想使用 case 语句

Answer 1

使用 LEFT 连接代替 INNER 连接并在 ON 子句中设置条件：

LEFT JOIN (
  SELECT DISTINCT applicationno 
  FROM impObjects WITH (NOLOCK) 
  WHERE objectType in (2,6) AND name = 'Version1' AND checksumid = CHECKSUM(N'Version1')
) AF ON AF.applicationno = Ta.applicationno AND dbk.etype = 1

并添加一个 WHERE 子句：

WHERE dbk.etype IN (1, 2)

Answer 2

因为你实际上并没有从那个子查询中选择任何东西，所以当指定为半连接时会好得多，例如 EXISTS. 然后你可以简单地使用 OR:

WHERE dbk.etype = 2
  OR EXISTS (SELECT 1
      FROM impObjects AF
      WHERE AF.objectType in (2, 6)
        AND AF.name = 'Version1'
        AND AF.checksumid = CHECKSUM(N'Version1')
        AND AF.applicationno = Ta.applicationno   -- this line is the join condition
  )

或者，如果 etype 有更多可能的值，则：

WHERE dbk.etype = 2
  OR (dbk.etype = 1 AND EXISTS (SELECT 1
      FROM impObjects AF
      WHERE AF.objectType in (2, 6)
        AND AF.name = 'Version1'
        AND AF.checksumid = CHECKSUM(N'Version1')
        AND AF.applicationno = Ta.applicationno   -- this line is the join condition
  ))

仅当特定列的值为 1 时才考虑内部联接，如果该特定列的值为 2 则不考虑联接

Consider a inner join only if value from a particular column is 1 and don't consider the join if the value of that particular column is 2

sql

sql-server

join

inner-join

left-join