按条款分组并具有最高记录-MYsql

Question

I have written the following SQL query which works great

SELECT  W.LineItems_LineItemID
     , P.CurrentRate
     , P.CurrentEffectiveDate 
  FROM WorkOrderLineItems W 
  JOIN PayScaleLoaclJObCodes P 
    ON P.JobCodeID = W.LineItems_LineItemID 
 WHERE P.PayScalesLocal_ID = 29
   AND W.WorkOrderCurrent_WorkOrderID = 120420
   AND P.CurrentEffectiveDate <= '2018-05-27' 
 ORDER 
    BY P.CurrentEffectiveDate DESC

Shows following results

Is there a way to return only a single that is the Top record, I do not want to show multiple records only the first record in the resulset

Answer 1

SELECT TOP 1 W.LineItems_LineItemID, P.CurrentRate, P.CurrentEffectiveDate 
  FROM WorkOrderLineItems W 
  JOIN PayScaleLoaclJObCodes P ON P.JobCodeID = W.LineItems_LineItemID 
  WHERE P.PayScalesLocal_ID = 29 AND W.WorkOrderCurrent_WorkOrderID = 120420
  AND P.CurrentEffectiveDate <= '2018-05-27' 
  ORDER BY P.CurrentEffectiveDate DESC

The SELECT TOP clause is used to specify the number of records to return. For your case all you would need is TOP 1 for one.

OR

SELECT W.LineItems_LineItemID, P.CurrentRate, P.CurrentEffectiveDate 
  FROM WorkOrderLineItems W 
  JOIN PayScaleLoaclJObCodes P ON P.JobCodeID = W.LineItems_LineItemID 
  WHERE P.PayScalesLocal_ID = 29 AND W.WorkOrderCurrent_WorkOrderID = 120420
  AND P.CurrentEffectiveDate <= '2018-05-27' 
  ORDER BY P.CurrentEffectiveDate DESC 
  LIMIT 1