Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
What is the excution order in Query like:
SELECT * FROM [users] WHERE [userid] = 50001 AND [username] = 'new user'
My question is what will be matched for first – [userid] or [username].
and so will affect the execution time.
Any suggesetion to improve this query will be appriciated.
The answer depends on the indexes that you make available to the SQL engine. If
useridis indexed butusernameis not, the engine is likely to start withuserid; ifusernameis indexed butuseridis not, then the engine would probably start with the name; if both fields are indexed, the engine will search that index, and look up the rows by internal ids. Note that all of this is highly dependent on the RDBMS that you are using. Some engines would forego index searches altogether in favor of full table scans when the number of rows is low.