Query Optimisation

Reading an execution plan, and why the same result can take a thousand times longer.

0 of 23 answered

• Not triedCounting all the rowsFoundation
• Not triedLIMIT with no ORDER BYFoundation
• Not triedReading the planFoundation
• Not triedWhat SELECT * costsFoundation
• Not triedWhat SELECT * costs in real codeFoundation
• Not triedAn index that will not be usedCore
• Not triedFast on the laptop, slow on the serverCore
• Not triedThe cost of fourteen indexesCore
• Not triedThe index that was ignoredCore
• Not triedThe OR that lost the indexCore
• Not triedThe wildcard at the wrong endCore
• Not triedA plan that used to be goodChallenge
• Not triedA sequential scan that is the right planChallenge
• Not triedA type mismatch that costs a scanChallenge
• Not triedEstimated 12, actual 900,000Challenge
• Not triedThe index that answered the whole queryChallenge
• Not triedThe index that is missingpart of The dashboard that got slower every weekChallenge
• Not triedWhat LIMIT 20 does and does not savepart of The dashboard that got slower every weekChallenge
• Not triedWhich column goes firstChallenge
• Not triedWhich table to drive frompart of The dashboard that got slower every weekChallenge
• Not triedWhich table to filter firstChallenge
• Not triedWhy page 5000 is slowChallenge
• Not triedWhy the planner chose badlypart of The dashboard that got slower every weekChallenge