unionM,N: The row refers to the union of the rows with id values of M and N. derivedN: The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause. subqueryN: The row refers to the...
Depending on thedetails of your tables, columns, indexes, and the conditions in your WHEREclause, 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 seve...
<derivedN>:ID值n的行的派生表结果,派生表可能是从FROM子句中的一个子查询生成的(The row refers to the derived table result for the row with an id value of N. A derived table may result, for example, from a subquery in the FROM clause.)。 <subqueryN>:ID值n的行的物化子查询结果。 4....
SQL- Where Clause: Answer and Explanation: The purpose of ''Where'' clause in a query is to specify, to limit and to filter a condition when getting data from a table. Tables can be either be... Learn more about this topic:
show_upper_qual(((HashJoin *) plan)->hashclauses, "Hash Cond", planstate, ancestors, es); show_upper_qual(((HashJoin *) plan)->join.joinqual, "Join Filter", planstate, ancestors, es); if (((HashJoin *) plan)->join.joinqual) show_instrumentation_count("Rows Removed by Join Fil...
This type of join is usually used for queries with the EXISTS clause. When you view execution plans of hash join operations, you also need to focus on the child nodes. hash cond: the join condition. Example: hash cond(tmp.a=tmp1.b). hash key: the key that is used for hash ...
Run the EXPLAIN command to inspect the planned execution path for your SQL query. Look at the tables order MySQL chose for the execution. Does it makes sense? If not, ask yourself why did MySQL get it wrong, what's missing? Find the conditions in the WHERE clause which are the most se...
Sequential ScanscanAmazon Redshift relation scan or table scan operator or step. Scans whole table sequentially from beginning to end; also evaluates query constraints for every row (Filter) if specified with WHERE clause. Also used to run INSERT, UPDATE, and DELETE statements. ...
<derivedN>: 这行指出派生表结果集在这行中的id值为N。A derived table may result, for example, from a subqueryin the FROM clause. <subqueryN>: 该行指的是物化查询在这行的ID值为N。 SeeSection 9.2.1.18.2,“Optimizing Subqueries with Subquery Materialization”. ...
Plan nodes that refer to execution on compute nodes are prefixed with XN in the EXPLAIN output. info character(400) Qualifier and filter information for the plan node. For example, join conditions and WHERE clause restrictions are included in this column. Sample queries Consider the ...