ExampleFollowing is an example of the EXPLAIN statement with ANALYZE −EXPLAIN ANALYZE SELECT * FROM CUSTOMERS; It displays the output that includes more timing and cost-related details as shown below −EXPLAIN –> Table scan on CUSTOMERS (cost=0.35 rows=1) (actual time=0.070..0.070 rows=...
[转]Oracle执行计划（ExplainPlan）说明 [转]Oracle执⾏计划（ExplainPlan）说明 原⽂地址:http://langgufu.iteye.com/blog/2158163 如果要分析某条SQL的性能问题，通常我们要先看SQL的执⾏计划，看看SQL的每⼀步执⾏是否存在问题。如果⼀条SQL平时执⾏的好好的，却有⼀天突然性能很差，如果排除了...
Example: Execute the following statement to check the execution plan of a query on a partitioned parent table with one partition scanned. EXPLAIN SELECT * FROM public.hologres_parent; The following figure shows the returned result. Query data by using a foreign table If you query data by usi...
Nested Loop nloop Least optimal join; mainly used for cross-joins (Cartesian products; without a join condition) and some inequality joins. Hash Join hjoin Also used for inner joins and left and right outer joins and typically faster than a nested loop join. Hash Join reads the outer tabl...
Example 1-4, "EXPLAIN PLAN Output"is an example of the plan table output when using theUTLXPLS.SQLscript. If you have specified a statement identifier, then you can write your own script to query thePLAN_TABLE. For example: Start with ID = 0 and givenSTATEMENT_ID. ...
Example: int a,b,c; In this statement,comma is a separator and tells to the compiler that these (a, b, and c) are three different variables. 2) Comma (,) as an operator Sometimes we assign multiple values to a variable using comma, in that case comma is known as operator. ...
The performance of the EXPLAIN statement is mostly affected by the factor of the time taken for the creation of the temporary tables. While executing query statements that include the subexpression or nested queries, there might be a necessity of creation of the internal temporary tables by the ...
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...
(Try writing such a statement if you don’t see it intuitively). Therefore, you can just find the enclosing scope’s boundaries, and the rest is easy. Notice in the example above, the UNION is over <union3,5>, which includes the row with id 4 – it includes every row between 3 ...
FAST'SLOW' indicates that the scan is expected to progress slowly over the table. For example, if the scan is the outer of a nested loop join). 'FAST' indicates that the scan is expected to progress with higher speed. This information is used to group scans together for efficient sharing...