判断接收的参数是否为null解决思路

判断接收的参数是否为null
 
  接收四个参数，判断四个参数是否为null，根据判断结果，查询数据库，但是没有按照设想执行，这是什么原因？？
  sybm=request("sybm")
  sydd=request("sydd")
  jdyf=request("jdyf")
  syr=request("syr")
  set rs_cjtzd =server.createobject("ADODB.RecordSet")
  if (IsNull(sybm) and IsNull(sydd) and IsNull(syr)) then
  sql_cjtzd="select * from jdjzjh where sybm is null and sydd is null and syr is null and jdyf='"&jdyf&"'"
  end if
  if ((Not IsNull(sybm)) and IsNull(sydd) and IsNull(syr)) then
  sql_cjtzd="select * from jdjzjh where sybm='"&sybm&"' and sydd is null and syr is null and jdyf='"&jdyf&"'"
  end if
  if ((Not IsNull(sybm)) and (Not IsNull(sydd)) and IsNull(syr)) then
  sql_cjtzd="select * from jdjzjh where sybm='"&sybm&"' and sydd='"&sydd&"' and syr is null and jdyf='"&jdyf&"'"
  end if
  if ((Not IsNull(sybm)) and (Not IsNull(sydd)) and (Not IsNull(syr))) then
  sql_cjtzd="select * from jdjzjh where sybm='"&sybm&"' and sydd='"&sydd&"' and syr='"&syr&"' and jdyf='"&jdyf&"'"
  end if
  rs_cjtzd.open sql_cjtzd,conn,1,1


------解决方案--------------------

VBScript code

sybm = Trim(request("sybm"))
sydd = Trim(request("sydd"))
jdyf = Trim(request("jdyf"))
syr = Trim(request("syr"))

If sybm = "" Then sybm = Null
If sydd = "" Then sydd = Null
If jdyf = "" Then jdyf = Null
If syr = "" Then syr = Null

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