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Questions tagged [explain]

Explain is a SQL command that shows the execution plan of a query.

Explain is an useful command used in various Database servers(like Oracle, MySQL, PostgreSQL, etc). It shows the execution plan of a query.

Oracle: 

EXPLAIN PLAN FOR SELECT …

PostgreSQL, MySQL:

EXPLAIN SELECT …

MSSQL doesn't support explain, but uses

"SET SHOWPLAN_TEXT ON".

instead.

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Hive View query is not using partition

I have hive tables and views on top of that tables . When executing query on Table using where clause for partition columns , I see from explain plain that query is using partition column . But same query when running on view , it is showing from…
Dibakar Paul
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sql plan discrepancy in DBMS_XPLAN.DISPLAY_CURSOR

Running on Oracle 12.1 I am looking for SQL with full table scans in their plans. When I look in: select * from V$SQL_PLAN where sql_id = '89p47f9wnnwg9' I get 21 rows back, one of them with TABLE ACCESS FULL However, if I call this for the same…
OldProgrammer
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Are query execution plans stored anywhere in postgresql?

I am trying to figure out if PostgreSQL query execution plans are stored somewhere (possibly as complimentary to pg_stat_statements and pg_prepared_statements) in a way they are available for longer than the duration of the session. I understand…
chi
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MySQL Index and Explain Plan

I have this query: SELECT * FROM dwDimDate d LEFT JOIN tickets t FORCE INDEX FOR JOIN (idx_tickets_id_and_date) ON DATE_FORMAT(t.ticket_date, '%Y%m%d') = d.date_key LEFT JOIN sales s ON s.ticket_id = t.ticket_id WHERE d.date_key BETWEEN 20130101…
hyphen
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How to find the time for each step of the process in Spark

I use the following function written in PySpark to log steps in a SQL table. def log_df_update(spark,IsComplete,Status,EndDate,ErrorMessage,RowCounts,StartDate,FilePath,tablename): import pandas as pd l =…
Raj
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Making radix sort in-place - trying to understand how

I'm going through all the known / typical sorting algorithms (insertion, bubble, selection, quick, merge sort..) and now I just read about radix sort. I think I have understood its concept but I still wonder how it could be done in-place? Let me…
eyesima
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Mongo - How to explain query without executing it

I'm new to Mongo and have searched but don't see a specific answer. I understand that Mongo explain method will execute the query in parallel with possible access plans and choose a winning plan based on execution time. The Best Practices Guide…
Jim Fletcher
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Explaining the Explain in teradata

Explain sel * from sandbox.comapny_employees ce left join sandbox.comapny_age ca on ce.age=ca.age and ce.age>42 some times its really confusing to understand how explain plan was created. below explain plan totally skipped the…
dev
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MySQL Performance Degrades during Concurrent Stored Proc Execution

Machine Specs : macOS Sierra, Version 10.12.5, Memory 8 GB MySQL Version: MySQL Enterprise Server - Advanced Edition (Commercial)3 innodb_version : 5.7.18 Problem : When same stored procedure is called concurrently by different sessions, the…
DeeJay14
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Why is UIView removed from heirarchy after presenting view controller?

Ok I just ran into something bizarre. I've got my app controller dependency injecting a view (header) into a view controller. That view controller presents another view controller modally and dependency injects it's own header for the presenting…
Aquila Sagitta
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explains shows fast execution time, but running the query never returns

I have a query that seems to never return. When I run explain on that query, it shows me executionStats.executionTimeMillis of 27ms, and that the initial input-stage is IXSCAN that should return 4 objects only. I've confirmed that querying for the…
marmor
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Explain this Kotlin function structure

I am working with this Kotlin function. I know that we have a function called mPasswordView!!.setOnEditorActionListener, that take parameter TextView.OnEditorActionListener, but what's that after it? we have curly brackets inside parameter?…
Vlad Skurtolov
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how to understand postgres EXPLAIN output

EXPLAIN SELECT a.name, m.name FROM Casting c JOIN Movie m ON c.m_id = m.m_id JOIN Actor a ON a.a_id = c.a_id AND c.a_id < 50; Output QUERY PLAN …
tarun14110
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mysql difference in number of rows scanned

I have a query : mysql> explain SELECT * FROM OTHERS_TINY_URL_TBL WHERE LINK_TYPE = 'BITLY' AND URL_SHORTNER_ID = '5434e3b9e4b03aa06f25da11' AND MODIFIED_TM >= '2016-03-13 21:09:43' AND MODIFIED_TM <= '2017-03-13…
sudeepdino008
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Clarification of join order for creation of temporary tables

I have a large query in mysql that involves joining multiple tables together. It's too slow, so I've done "explain" and see that it's creating a temporary table, which I suspect of taking most of the execution time. I found some related…
Brick
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