WHERE 子句对性能的影响

Question

I am no SQL expert and I am trying to optimize a query I'm making. Assume the following situation: I want to extract all the unpaid bills for a list of clientID. My current query looks a bit like this:

SELECT CLIENT_ID, BILL_ID, BILL_PAID  
FROM T_BILLS 
WHERE CLIENT_ID IN [LIST OF IDs] 
  AND BILL_PAID = 'No' 

My first thinking was that the second where condition (BILL_PAID = 'No') is reducing the number of rows returned thus making the query faster. My company server has a time limit for running SQL Queries. Right now I'm busting it. I know I could slice my LIST OF IDs into smaller lists but before doing so I was wondering if eliminating the second where clause could help. The logic being I would get more data but that might require less computing. The extra data could easily be filtered out later with excel.

Answer 1

As mentioned in comments if you don't have indexes on CLIENT_ID and BILL_PAID then add them. Also consider change BILL_PAID type from string to int or tiny int (model enum or boolean type if applicable) to bust the index on that column even more.