Without a date clause limiting the results to eg the most recent 2years worth of orders, you will get all orders for all time. This can be absolutely dire for performance if you don't have a where clause that significantly narrows down the result set in the View Query.Ĭonsider an example view that contains Customer Orders and Details. Your query will then be run against this table. With the Temptable option MySQL will run the View Query and store the results in a temporary table. So when using the Merge algorithm, the performance of your View is only as good as the query that creates it. Trying to use any of these will force MySQL to use the below Temptable Algorithm. One thing to be away of is that you cannot use the merge algorithm if you have any of the following in your View Query:ġ.Aggregate functions (SUM(), MIN(), MAX(), COUNT(), and so forth) It is the result set of a stored query in the database server that can then be queried like a table.Ĭonsider this example query to return actors and films they are in ( using the Sakilla sample Database ).Įnter fullscreen mode Exit fullscreen mode While this sounds great it can be an absolute disaster performance-wise for your database.įirst off what exactly is a Database View ? The common solution across their documentation for both issues is to create Views to simplify tables, hide joins etc. Some of these BI tools also allow users to create their own "Queries" with the tables, which can be confusing as they wont know the schema. You can only do this (the trigger is irrelevant) when inserting in a partitioned view, which is view that can UNION ALL data in which the underlying tables have proper CHECK constraints that are disjoint together with a primary key, so an INSERT would unmistakably go in one underlying table. The recursive SELECT part must reference the CTE only once and only in its FROM clause, not in any subquery. I tend to err on the side of caution and do not want to expose my table structure to these applications. The prohibition on DISTINCT applies only to UNION members UNION DISTINCT is permitted.
#Mysql create view with union trial
Recently I have had the opportunity to trial several third party BI tools which integrate with my database. MySQL UNION operator can combine two or more result sets hence we can use UNION operator to create a view having data from multiple tables. Other flavours of SQL (eg SQL Server, PostgreSQL, SQLite) may be slightly different, SQL Server in particular has Indexed Views which can improve performance.
Optional second argument for passing options:* cancel: if true, cancel query if timeout is reached.This article is relevant to MYSQL. The UNION operator is a set operator that combines result sets of two or more SELECT statements into a single result set. Useful for complex queries that you want to make sure are not taking too long to execute. The error contains information about the query, bindings, and the timeout that was set. Sets a timeout for the query and will throw a TimeoutError if the timeout is exceeded. If you don't want to manually specify the result type, it is recommended to always use the type of last value of the chain and assign result of any future chain continuation to a separate variable (which will have a different type).
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