If the number of duplicates relative to the size of the table is small, this approach may make your delete faster. This is because it can swap a full scan of your table for rowid lookups: If your table has hundreds of millions of rows or more, this could massively reduce how long the...
因此,就需要DBA来不断的优化SQL。 对于查询情况,其实MySQL提供给我们一个功能来引导优化器更好的优化,那便是MySQL的查询优化提示(Query Optimizer Hints)。比如,想让SQL强制走索引的话,可以使用 FORCE INDEX 或者USE INDEX;它们基本相同,不同点:在于就算索引的实际用处不大,FORCE INDEX也得要使用索引。 EXPLAIN SEL...
DELETE: A delta file contains the txnid and rowid fields, both of which have a value of the BIGINT type. The rowid field indicates the deleted row in the base files of the transactional table. The txnid field indicates the delete operation that is performed on the row. For example, ...