the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can
MySQL wasable to do a LEFT JOIN optimization on the query and does not examine morerows in this table for the previous row combination after it finds one row thatmatches the LEFT JOIN criteria. Here is an example of the type of querythat can be optimized this way: Assumethat is defined ...
the MySQL optimizer considers many techniques to efficiently performthe lookups involved in an SQL query. A query on a huge table can be performedwithout reading all the rows; a join involving several tables can be performedwithout comparing every combination of rows. The set of operations...
Access method – The way in which the data is being accessed, via either a table scan or index access. Join method – The method (e.g., hash, sort-merge, etc.) used to join tables with each other. Join type – The type of join (e.g., outer, anti, semi, etc...
Join types Join types define the way in which the join operation occurs. CrossJoin –Produces the Cartesian product of the two tables joined. InnerJoin –Selects records that have matching values in both tables. LeftJoin –Selects all records from the left table and the matching records from...
EXPLAIN returnsa row of information for each table used in the SELECT statement. It lists thetables in the output in the order that MySQL would read them while processingthe statement. MySQL resolves all joins using a nested-loop join method. Thismeans that MySQL reads a row from the first...
If SQL query performance is poor or query results do not meet expectations, you can execute the EXPLAIN and EXPLAIN ANALYZE statements in Hologres to obtain execution plans of query statements. This way, you can optimize query statements or database structures. This topic describes how to execute...
Part of[EPIC] CompleteSQL EXPLAINTree Rendering#14914 @irenjjadded a newtreeexplain mode in#14677. Now we need to add support for different types of operators. Here is an example of how to see the new explain plans: setdatafusion.explain.format='tree';createtablefoo(xint, yint)asvalues(1...
BatchGet RPC request is sent in the prefetch step. Get RPC request is sent when the insert on duplicate statement executes duplicate update. backoff: Contains different types of backoff and the total waiting time of backoff. IndexJoin The IndexJoin operator has 1 outer w...
indexed but not only roll_no. MySql can use class or class and roll_no for the index but not only roll_no). There is only one row in the address table for each combination in the student_detail table(We used the id of address to join and it is the primary key in the address ...