![]() Oracle Database is being used by many companies in the IT industry for transaction processing, business analytics, and also business intelligence app purposes.įirst commercialized in 1979, it was built around a relational database where data could be accessed by users via an application or Structured Query Language (SQL). It’s commonly known as Oracle Database or Oracle DB. Oracle is one of the largest vendors of Relational Database Management Systems (RDBMS) in the market today. The following article will put these two rivals under the microscope to try and determine which is more capable of handling the ever-growing list of challenges in the IT space. ![]() Oracle Database has been a globally recognized and appreciated solution for decades, but there is a rising star called PostgreSQL, which is gaining the confidence of developers from all around the world. Interestingly, this also applies to the tech and software world. This changed in PostgreSQL 12, where CTEs are no longer materialized and are treated like sub-queries.一篇 2021年1月份国外的一篇文字关于评论 PG VS ORACLE的文字.看完觉,从技术的角度看,有点LOWERĪs the saying goes, change is the only constant in life. Keep in mind that the database has to evaluate all the predicates, so adding too many might make a query slower.īefore PostgreSQL 12, Common Table Expressions (aka CTE) were materialized. It should only be used to provide more information to the optimizer that can improve the query performance. You might be able to improve the performance of a query by providing additional information to the optimizer, using what I like to call, a "Faux Predicate".ĭb=# ( SELECT * FROM sale WHERE modified < ' asia/tel_aviv' AND created < ' asia/tel_aviv' ) QUERY PLAN - Index Scan using sale_created_ix on sale (cost=0.44.4.52 rows=1 width=276) Index Cond: (created < ' 00:00:00+02'::timestamp with time zone) Filter: (modified < ' 00:00:00+02'::timestamp with time zone)Īfter we added the "Faux Predicate" the optimizer decided to use the index on the created field, and the query got much faster! Note that the previous predicate on the modified field is still being evaluated, but it's now being applied on much fewer rows.Ī "Faux Predicate" should not change the result of the query. In some circumstances, you have knowledge of your data that the optimizer does not have, or cannot have. In this case, it might conclude that it makes more sense to use an index rather than scan the entire table. ![]() For example, if you apply a filter on a column with a unique constraint, the optimizer knows it can expect exactly one row for each value. To generate a good execution plan, the optimizer utilizes metadata and statistics it has on your data. For example, the optimizer decides whether to use a specific index or not, in what order to execute a join, which table to filter first, and so on. The execution plan describes how the database in going to access the data necessary to satisfy the query. The query optimizer looks at your SQL and generates an execution plan. One of the most important components in database implementations, and usually the one that makes one database better than the other, is the query optimizer. Using BETWEEN incorrectly might produce overlapping results, for example, counting sales twice in two different periods. SELECT * FROM sales WHERE created >= '' AND created < ''
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