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Why does inner join perform faster than left join?
OPTION (FORCE ORDER) is a query hint that forces the optimizer to build the execution plan with the join order you provided in the query. If INNER JOIN starts performing as fast as LEFT JOIN, it’s because: In a query composed entirely by INNER JOIN s, the join order doesn’t matter.
Why are inner join queries kill server performance?
Have seen inner queries kill server performance because two large (millions to tens of millions of rows) tables are inner joined both pulling a large number of fields and no covering index exists. The biggest issue though, doesn’t seem to appeaer in the discussions above.
Why do we have to use inner join in SQL?
If those 10 tables had been inner-joined together, then the query optimizer would have to join them all even though your query itself doesn’t need 7 out of 10 of the tables. That’s because the inner joins themselves might filter down the data, making them essential to compute.
When to drop outer join from execution plan?
When using an outer join, the optimizer is always free to drop the outer joined table from the execution plan if the join columns are the PK of the outer table, and none of the outer table columns are referenced outside of the outer join itself. For example SELECT A.* FROM A LEFT OUTER JOIN B ON A.KEY=B.KEY and B.KEY is the PK for B.
How to optimize inner join in SQL Server?
BUT, the optimizer may also optimize a left join sub-optimally as a left semi join. To make it choose the one you want you can use the force order hint. Try both queries (the one with inner and left join) with OPTION (FORCE ORDER) at the end and post the results.
Which is better inner join or where in MySQL?
Inner Join (V2) is slightly better than Where (V1). This might indicate that MySQL could use better optimization technique (s) in the case of Inner Join. [Note: other RDMBS can have the same performance for the two cases]. Having indexes on both sides of the join has the best performance.