query-optimization – Read For Learn

SQL: How to properly check if a record exists

February 8, 2022 by admin

It’s better to use either of the following: The first alternative should give you no result or one result, the second count should be zero or one. How old is the documentation you’re using? Although you’ve read good advice, most query optimizers in recent RDBMS’s optimize SELECT COUNT(*) anyway, so while there is a difference … Read more

Hive Map-Join configuration mystery

January 31, 2022 by admin

These parameters are used to make decision on when to use Map Join against Common join in hive, which ultimately affects query performance at the end. Map join is used when one of the join tables is small enough to fit in the memory, so it is very fast. here’s the explanation of all parameters: hive.auto.convert.join When this parameter set … Read more