To specify optimizer hints to be used in the SELECT statement. Support for setting optimizer hints on databases.ĪctiveRecord::QueryMethods#optimizer_hints
#Mysql optimizer hints full#
The FULL hint instructs that a full table scan should be performed on the students table. In the example above, the + before the comment tells the database server that this is a hint.
execute ( sql ) (0.4ms) Select /*+ FULL(students) */ first_name Pry(main)> * Where year = 1 " => "Select /*+ FULL(students) */ first_name \n From students \n Where year = 1 \n " pry(main)> ActiveRecord :: Base. Example pry(main)> sql = "Select /*+ FULL(students) */ first_name To use Optimizer Hints before Rails 6, we had to use raw SQL queries. We, as an application architect, might know information about our data that the optimizer does not.Īnd that knowledge, on some occasions, can help us to choose a more optimized execution plan than the optimizer. The Optimizer Hints give us the opportunity to influence the optimizer. Which are used to calculate the said cost and pick an execution plan. The optimizer has such internal statistics The optimizer chooses the plan with the lowest cost in terms of I/O,Ībout our objects like the number of rows,
The query optimizer attempts to generate the most optimal execution plan for a SQL statement. An execution plan describes a recommended method of execution for a SQL statement.
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