using index:只用到索引,可以避免访问表. using where:使用到where来过虑数据. 不是所有的where clause都要显示using where. 如以=方式访问索引. using tmporary:用到临时表 using filesort:用到额外的排序. (当使用order by v1,而没用到索引时,就会使用额外的排序) range checked for eache record(index m...
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...
If you want to query execution plans with higher readability, we recommend that you upgrade your Hologres instance to V1.3.4x or later. EXPLAIN Syntax You can execute the following EXPLAIN statement to query the execution plan that is estimated by the QO: EXPLAIN <sql>; Example In this ...
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...
Description:For queries with HAVING clause EXPLAIN may not show real plan used (suggesting other one). This makes troubleshooting more complex. Here is a simplified example (based on real life case where query execution time was very different, while EXPLAIN had not let to see why), on MySQL...
SQL- Where Clause: Answer and Explanation: Become a Study.com member to unlock this answer!Create your account View this answer The purpose of ''Where'' clause in a query is to specify, to limit and to filter a condition when getting data from a...
Example 19-4 Using EXPLAIN PLAN with the INTO ClauseEXPLAIN PLAN INTO my_plan_table FOR SELECT last_name FROM employees; You can specify a statement Id when using the INTO clause.EXPLAIN PLAN SET STATEMENT_ID = 'st1' INTO my_plan_table FOR SELECT last_name FROM employees; ...
re new to the data set this takes time. Even if the data are clear, if this isn’t a query we wrote in the first place; it can be hard to decide where to add additional joins and where clauses, etc., and not mess up the entire result. Have no fear, the SQL AI Assistant is...
If you run an ANALYZE TABLE on the table in question, you might find that the number of rows it returns are not even close to the actual number in the real table. To fix this you could use a different type of JOIN or even go so far as to reorder your tables in your FROM clause...
Cause: A GROUP BY column in the query is not present in the GROUP BY clause of the materialized view. This usually requires a join back to a third table. Action: No action required. QSM-01059 HAVING clause in the query block is malformed Cause: An illegal HAVING clause has been specif...