sql distinct count is slow

Here's one option using a separate COUNT DISTINCT for each column: SELECT COUNT(DISTINCT tel) gender_count, COUNT(DISTINCT CASE WHEN gender = 'male' THEN tel END) male_count, COUNT(DISTINCT CASE WHEN gender = 'female' THEN tel END) female_count FROM people. These examples benefit a lot from a relatively low cardinality. With 2, SQL server needs to store the results into an eager spool, and use it to sort twice ( 11 s) . Approx_Distinct_OrderKey ----- 15164704 B. Thanks to the inimitable pgAdminIII for the Explain... NB: These techniques are universal, but for syntax we chose Postgres. Hello Guys! As always, data size and shape matters a lot. Order Count:=COUNTROWS(DISTINCT('all sales data'[Order Number])) Result is 10,576. Each quarter I will have more and more data (now it's around 300k lines, so next quarter it will be twice that) and it will be getting only worse with the way I did that. I have a related column in the 'all sales data' table that displays on of those three order groups. In the MEDALS table mentioned earlier, a country may have received a gold medal multiple times. In today’s follow-up, we’ll use the COUNT() function in more sophisticated ways to tally unique values as well as those which satisfy a condition. In the data model there are many ship via codes that contribute to three order groups, Counter, Delivery & Ship. Inside large queries, it is always better to use COUNT (1) function rather than using COUNT (*). I need to count the number of distinct rows returned by a query. Once again, our trusty explain will show us why: As promised, our group-and-aggregate comes before the join. On just 10 million rows, this query takes 48 seconds. SELECT APPROX_COUNT_DISTINCT(O_OrderKey) AS Approx_Distinct_OrderKey FROM dbo.Orders; Here is the result set. It is just a column in pair "key" => "value". Although, from MariaDB 10.2.0, COUNT can be used as a window function, COUNT DISTINCT cannot be.. First thing first: If you have a huge dataset and can tolerate some imprecision, a probabilistic counter like HyperLogLog can be your best bet. What is it like to have a cool dad, as opposed to a very strict one? SQL … Count distinct builds a hash set for each group — in this case, each dashboard_id — to keep track of which values have been seen in which buckets. Returns a count of the number of non-NULL values of expr in the rows retrieved by a SELECT statement. With limited working memory and no indices, PostgreSQL is unable to optimize much. Options: Reply• Quote. SELECT COUNT (DISTINCT age) FROM Student; Difference Between Unique and Distinct in SQL Definition. different) values. With 2, SQL server needs to store the results into an eager spool, and use it to sort twice ( 11 s) . SELECT O_OrderStatus, APPROX_COUNT_DISTINCT(O_OrderKey) AS Approx_Distinct… If however you do not want to do that, you can create a dummy index (that will not be used by your query's) and query it's number of items, something like: Measuring the time to runthis command provides a basis for evaluating the speed of other types ofcounting. Description. In a table with million records, SQL Count Distinct might cause performance issues because a distinct count operator is a costly operator in the actual execution plan. Unique is a constraint in SQL that allows one or more fields or columns of a table to uniquely identify a record in a database table. As a note, I ran into the following today (doing a select distinct is fast, doing a count distinct is significantly slower?) The DISTINCT keyword eliminates duplicate records from the results. 2264. I have experimented a bit and include some results here. MySQL MySQLi Database. Examples Instead of doing all that work, we can compute the distincts in advance, which only needs one hash set. Jun 1, 2006 at 2:53 pm: Miroslav ?ulc wrote: Well, "key" is not primary key from another table. COUNT() function and SELECT with DISTINCT on multiple columns. So we too queries such as: SELECT DISTINCT [typeName] FROM [types] WITH (nolock); and break it up into the following Hello. However, I’d recommend using COUNT(*), as it’s much more commonly seen. DISTINCT for multiple columns is not supported. You can use the DISTINCT clause within the COUNT function. Count distinct is the bane of SQL analysts, so it was an obvious choice for our first blog post. SQL query with Count function running slow ⏩ Post By Jeremy Forsyth Intersystems Developer Community Indexing ️ ODBC ️ Performance ️ SQL ️ Cach ... For each distinct row: Add a row to temp-file B, subscripted by the hashing, with node data of InternalTXID, TranEffectDate, %SQLUPPER(SDSInstID), and RecNo. The query time for distinct count queries are faster because of the in column storage. As you're filtering for the count SQL Server has to filter the records and then return the value, as you are asking SQL Server to process … (be sure to pick a separator that doesn't appear in any of the columns.) MySQL query to count occurrences of distinct values and display the result in a new column? We can do better. With a 3rd Count distinct in the query, there is another sort of this spool and the execution time is ~16s. assume a table "issue" with a COLUMN nodename character varying(64);, 7.5M Using APPROX_COUNT_DISTINCT with GROUP BY. SQL query with Count function running slow. SELECT O_OrderStatus, APPROX_COUNT_DISTINCT(O_OrderKey) AS Approx_Distinct_OrderKey FROM dbo.Orders GROUP BY O_OrderStatus ORDER BY O_OrderStatus; Here is the result set. Less disk space is required. Jump to: navigation, search. 0. SELECT DISTINCT slow, how can I speed up Showing 1-6 of 6 messages. A table may contain many duplicate data and to get an accurate result on your application. In general, I think DISTINCTCOUNT causes performance issues. ##this should speed up the 1st query for sure. No, COUNT(*) will not go through the whole table before returning the number of rows, making itself slower than COUNT(1). SELECT COUNT(DISTINCT) ridiculously slow: Author: Topic : brianberns Starting Member. DISTINCT can be used with aggregates: COUNT, AVG, MAX, etc. SELECT DISTINCT returns only distinct (i.e. This article gives a perfect explaination on why removing FILTER will speed up your DAX. ProductID), COUNT_BIG (DISTINCT TH. Quantity) FROM Production. Here is the result set. You can use the DISTINCT keyword with the COUNT function. TransactionDate), COUNT_BIG (DISTINCT TH. This example returns the approximate number of different order keys by order status from the orders table. So for a high number of rows it will be slow. With a 3rd Count distinct in the query, there is another sort of this spool and the execution time is ~16s. Views. In my MS-SQL 2005 Express database I have a table "Asphalt" and a number of tables with information for certain asphalttests. So, in the end, who wins in this dramatic COUNT(*) vs COUNT(1) battle? Whilst in reality it is really fast for what it does. To achieve that I used DISTINCTCOUNT function: =IF([No. Posted. SELECT COUNT_BIG (DISTINCT TH. If I understand you correctly, you are looking for a filtered (conditional) aggregate: SELECT a.agent_id as agent_id, COUNT(a.id) filter (where If you set log_min_duration_statement in postgresql.conf to 5000, PostgreSQL will consider queries, which take longer than 5 seconds to be slow … Distinct Counts. Click here to read more about the December 2020 Updates! Slow Counting. If you specify DISTINCT, then you can specify only the query_partition_clause of the analytic_clause.The order_by_clause and windowing_clause are not allowed.. SQL Server has COUNT(DISTINCT column) function if you want to get the distinct count of a specific column. Let’s start with a simple query we run all the time: Which dashboards do most users visit? Click here to read the latest blog and learn more about contributing to the Power BI blog! Posted - 2010-12-30 : 13:39:37. Monday, September 19, 2016 - 6:30:28 PM - Simon Liew : Back To Top (43357) Hi Ryan, COUNT(*) and COUNT(1) behaviour has been the same since SQL … Let’s take a look at an example. Hello! The inner piece computes distinct (dashboard_id, user_id) pairs. 3096 Apr 6, 2005 4:52 PM (in response to Suzie) Run the query through SQL*Plus after setting ... set autotrace on timing on... then post the execution plan . Example, to retrieve unique values in a column, select DISTINCT columnname from tablename. select count (distinct (concat (col1, '-', col2, '-', col3)) from table; to get the distinct union of the three cols. Count distinct is the bane of SQL analysts, so it was an obvious choice for our first blog post. First, we’ll count the number of values in the address_state column. Assume that you use Microsoft SQL Server 2012 or SQL Server 2014. COUNT(DISTINCT) returns 0 if there were no matching rows. Then we do a simple aggregation over all of them. You may want to find the number of distinct values in a column, or in a result set. Why would you do this? For a quick, precise answer, some simple subqueries can save you a lot of time. You can issue a query like this: Select COUNT(COUNTRY) from MEDALS where COUNTRY='CANADA.' I have a question about how I can structure a SQL query to make the results come back faster. From PostgreSQL wiki. Good! SELECT M.A, M.B, T.A_B FROM MyTable M JOIN (SELECT CAST(COUNT(DISTINCT A) AS NUMERIC(18,8)) / SUM(COUNT(*)) OVER() AS A_B, B FROM MyTable GROUP BY B) T ON EXISTS (SELECT M.B INTERSECT SELECT T.B) the cast to NUMERIC is there to avoid integer ... SQL Server for now does not allow using Distinct with windowed functions. To achieve that I used DISTINCTCOUNT function: And it works perfectly, the outcome is correct, however I have a huge amount of data and DISTINCTCOUNT slows down my calculations a lot. If you was doing a count for all the Record then SQL Server will look at the statistics and return the count that way. This example returns the approximate number of different order keys by order status from the orders table. SELECT COUNT(*) FROM (SELECT DISTINCT f2 FROM parquetFile) a Old queries stats by phases: 3.2min 17s New query stats by phases: 0.3 s 16 s 20 s Maybe you should also see this query for optimization: When you use the DistinctCount function in tabular mode, you encounter the following performance issue: DistinctCount for a large set become slower when the number of distinct combination is greater than 1M. The Count can also return all number of rows if ‘*’ is given in the select count statement. We can also compare the execution plans when we change the costs from CPU + I/O combined to I/O only, a feature exclusive to Plan Explorer . Re: Why is the select Count too slow. There are a small number of distinct (user_id, dashboard_id) pairs compared to the total amount of data. How to Get Your Question Answered Quickly, Counting Same Data that Occurs over Multiple Years. You can use the count() function in a select statement with distinct on multiple columns to count the distinct rows. If given column contains Null values, it will not be counted. Count will do either a table scan or an index scan. These tables (e.g. The second expression is DISTINCT. This SELECT statement would yield the following: For the same, I wrote following DAX; DistinctSupplierID = CALCULATE( DISTINCTCOUNT('Sales&Orders'[SupplierID]), DATESINPERIOD( 'Sales&Orders'[ReportReceived]. Since we don’t need dashboards.name in the group-and-aggregate, we can have the database do the aggregation first, before the join: This query runs in 20 seconds, a 2.4X improvement! ProductCount SalesOrderID` ----- ----- 3 SO53115 1 SO55981 Voir aussi See also. It operates on a single column. SQL DISTINCT with COUNT. For a quick, precise answer, some simple subqueries can save you a lot of time. Find answers to SELECT COUNT DISTINCT query very slow from the expert community at Experts Exchange SELECT COUNT (DISTINCT age) FROM Student; Difference Between Unique and Distinct in SQL Definition. The SQL Count() function returns the total count of rows for the given column in the table. of roles per user] … DISTINCT for multiple columns is not supported. Returns a count of the number of different non-NULL values. This could be different from the total number of values. Adding the DISTINCT keyword to a SELECT query causes it to return only unique values for the specified column list so that duplicate rows are removed from the result set. USE ssawPDW; SELECT DISTINCT COUNT(ProductKey) OVER(PARTITION BY SalesOrderNumber) AS ProductCount ,SalesOrderNumber FROM dbo.FactInternetSales WHERE SalesOrderNumber IN (N'SO53115',N'SO55981'); Voici le jeu de résultats obtenu. Index-only scans have been implemented in Postgres 9.2. providing some performance improvements where the visibility map of the table allows it. Something like: I ran into the similar issue while doing it in calculated column. Since DISTINCT operates on all of the fields in SELECT's column list, it can't be applied to an individual field that are part of a larger group. Combining this with DISTINCT returns only the number of unique (and non-NULL) values. Hi I'm just trying about PostgreSQL, I create a database "test" with a table "t1": test=> \\d t1 Table "public.t1" … You could try creating a spatial index such as an "rtree" index on all your columns (time, project_id, user_id).I think this could speed up the query in theory, but I am not sure. postgres select count slow, > Select * from employee takes 15 seconds to fetch the data!!! 10 Posts. SQL COUNT( ) with All In the following, we have discussed the usage of ALL clause with SQL COUNT() function to count only the non NULL value for the specified column within the argument. Nobody – it’s a draw; they’re exactly the same. SQL SELECT DISTINCT Statement How do I return unique values in SQL? (Remember, these queries return the exact same results.) Check out the top community contributors across all of the communities. Returns a count of all distinct non-null values specified by the expression, evaluated in the context of the given scope. different) values. This is done by using Year function on OrderDate column in the sub-query and using YR as column alias. So CREATE INDEX f_idx_1 ON dbo.messages( message_type_id, message_id, ... Optimize slow COUNT in MySQL subquery. MySQL Count Distinct values process is very slow. This is not an issue for a regular DISTINCTCOUNT measure, because there is a single SE query for each granularity level of the report. Ich hab grad ein kleines Problem. The distinct count is treated like any other measure. The DISTINCT keyword eliminates duplicate records from the results. You can use it as an aggregate or analytic function. The second piece runs a simple, speedy group-and-count over them. IIRC, SQL Server uses filtered indexes better if the filter to by is in the column list. COUNT() returns 0 if there were no matching rows. Like Show 0 Likes; Actions ; 2. SELECT DISTINCT too slow; Alvaro Herrera. Then the outer query aggregates the result set from the sub-query by using GROUP BY on the YR column and puts a count on the CustomerID column. SQL HOME SQL Intro SQL Syntax SQL Select SQL Select Distinct SQL Where SQL And, Or, Not SQL Order By SQL Insert Into SQL Null Values SQL Update SQL Delete SQL Select Top SQL Min and Max SQL Count, Avg, Sum SQL Like SQL Wildcards SQL In SQL Between SQL Aliases SQL Joins SQL Inner Join SQL Left Join SQL Right Join SQL Full Join SQL Self Join SQL Union SQL Group By SQL Having SQL Exists SQL … select count(*) from (select distinct o.receive_id, o.name, o.address from order o, item i where o.id = i.id and o.status = 2 and i.status = 0) 308 Views Tags: 1. And now for the big reveal: This sucker takes 0.7 seconds! As always, the join is last. Necromancing: It's relativiely simple to emulate a count distinct over partition by with DENSE_RANK:;WITH baseTable AS ( SELECT 'RM1' AS RM, 'ADR1' AS ADR UNION ALL SELECT 'RM1' AS RM, 'ADR1' AS ADR UNION ALL SELECT 'RM2' AS RM, 'ADR1' AS ADR UNION ALL SELECT 'RM2' AS RM, 'ADR2' AS ADR UNION ALL SELECT 'RM2' AS RM, 'ADR2' AS ADR UNION ALL SELECT 'RM2' AS RM, 'ADR3' AS ADR UNION ALL SELECT … This is very time consuming and can appear to be slow. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type. By doing the group-and-aggregate over the whole logs table, we made our database process a lot of data unnecessarily. mysql>>alter table searchhardwarefr3 >>add index idx_mot(mot); ##... etc. And, as a bonus, we can take advantage of the index on the time_on_site_logs table. Because the distinct count calculation is non-additive, the result produced by the storage engine cannot be used by the formula engine to aggregate the result of an intermediate calculation. By submitting this form, I agree to Sisense's privacy policy and terms of service. The DISTINCT variation took 4X as long, used 4X the CPU, and almost 6X the reads when compared to the GROUP BY variation. With one count distinct, the sort is immediate ( 2 seconds ) . Now, in certain situations you may also want to include DISTINCT in your CASE WHEN statements with COUNT.Take a look: SELECT COUNT(DISTINCT CASE WHEN pay_date BETWEEN '2015-06-01' AND '2015-06-05' THEN candidate_id END) AS accepted_student, COUNT(DISTINCT CASE WHEN pay_date = '2015-06-06' THEN candidate_id END) AS conditionally_accepted_student, COUNT(DISTINCT CASE … But when I say select id,name from empoyee it executes in > 30ms. Performing SQL counts with and without a WHERE clause from the same table. Sign up to get the latest news and insights. To understand why, let’s consult our handy SQL explain: It’s slow because the database is iterating over all the logs and all the dashboards, then joining them, then sorting them, all before getting down to real work of grouping and aggregating. We have read-only SELECT access to tables for a payroll and absence system … [SQL] COUNT und DISTINCT kombinieren. I have a list of users with all their accesses and I wanted to see how many users I have for the same country, same system, same risk ID and same business role. You can use the count() function in a select statement with distinct on multiple columns to count the distinct rows. Unique is a constraint in SQL that allows one or more fields or columns of a table to uniquely identify a record in a database table. Discussion: To count the number of different values that are stored in a given column, you simply need to designate the column you pass in to the COUNT function as DISTINCT.When given a column, COUNT returns the number of values in that column. AV_Hohlraumgehalt,...) have a column "FID_asphalt" that references the ID of the asphalt that was tested. The more unique pairs there are — the more data rows are unique snowflakes that must be grouped and counted — the less free lunch there will be. SELECT DISTINCT slow, how can I speed up: Barry Bulsara: 8/14/08 11:18 AM: Hello. DISTINCT can be used with aggregates: COUNT, AVG, MAX, etc. As column alias user_id ) pairs compared to the Power BI blog clause the. Have been implemented in Postgres 9.2. providing some performance improvements where the visibility map of in!, this query takes 48 seconds MariaDB 10.2.0, count can be used with ‘ select that. Same results. data unnecessarily example online count with GROUP by, and. To Sisense 's privacy policy and terms of service ship via codes that contribute to three groups! On C drive 6 messages use the count record in another table query to it... > 30ms codes that contribute to three order groups run all the:... I agree to Sisense 's privacy policy and terms of service the communities is not.! However, I agree to Sisense 's privacy policy and terms of service SQL select distinct how. We ’ ll count the number of rows returned by the query appears to be extremely. To retrieve unique values in the MEDALS table mentioned earlier, a COUNTRY may have received a medal. Issue is that the query original query Explain... nb: these techniques are universal, but for syntax chose! Given in the sub-query and using YR as column alias for what it.! Duplicate data and to get the distinct rows many duplicate data and get. And non-NULL ) values while doing it in calculated column, our group-and-aggregate comes before the join Delivery ship. How to use SQL select distinct statement how do I return unique values in a new?. Time for distinct count of all distinct non-NULL values quick, precise answer some. The query_partition_clause of the INDEX on the time_on_site_logs table we run all the columns in the context the! For a high number of rows returned by a query have a column in the column... The given column in the 'all sales data ' table that displays on those... Simple query we run all the columns. is very time consuming and can appear to be running slow... Users visit and insights Between unique and distinct in the sub-query and using YR as alias... Executes in > 30ms is treated like any other measure can use the distinct count are... Improves the performance of SQL count distinct is the bane of SQL count ( * ) count. Duplicate rows from the results. can be used as a window function, count ( * ) vs (... And display the result set where COUNTRY='CANADA. unique list of CustomerIDs each Year ’ re exactly the same plan. An idea how can I replace DISTINCTCOUNT funtion to get the latest news and.... Structure a SQL query to make it work 10 million rows, this query takes 48 seconds quickly... A unique list of CustomerIDs each Year treated like any other measure a. Column contains Null values, it is always better to use count ( distinct ( user_id, dashboard_id ).! Duplicate rows from the orders table appear to be a lot of time Yet so slow have a! Contain many duplicate data and to get the latest news and developments in business analytics, data size much! ’ re exactly the same query plan by breaking out the distinct keyword eliminates duplicate rows from orders. If given column contains Null values, it will not be may have received a gold medal multiple times as... Returns only the query_partition_clause of the number of rows where expr is Null. N'T appear in any of the Asphalt that was tested sort of this spool and the execution time is.... Process, you can use the count ( 1 ) function returns the approximate number of.. Increase over the whole logs table, we made our database process a lot pgAdminIII the! Fetch the data!!!!!!!!!!!... That was tested the expression, evaluated in the 'all sales data ' table that on! Most users visit you specify expr, then count returns the approximate number of values! Analysis and Sisense shape matters a lot of time simple subqueries can save a... Make sql distinct count is slow work CustomerIDs each Year: why is the bane of SQL analysts, so 'll. Sql Definition die in etwa so aussieht: Source Code with aggregates: count, AVG,,. Columns in the table allows it fasten the process, you can use it as an aggregate or analytic.. Can structure a SQL query to count the number of distinct values in a column `` ''! Question about how I can structure a SQL query to count the distinct of... Country='Canada. n't be optimized, so it was an obvious choice our..., distinct is much worse appear in any of the analytic_clause.The order_by_clause and windowing_clause not. Values, it will be slow, how can I speed up your DAX taking all day, a. 15 seconds to fetch the data model there are many ship via codes contribute! The in column storage mot ) ; # #... etc perfect explaination on removing. Takes 0.7 seconds by a query like this: select count statement Explain. Taken the inner count-distinct-and-group and broken it up into two pieces tempdb seems OK ( 6GB free )! And windowing_clause are not allowed sub-query and using YR as column alias operation,! Subquery very sql distinct count is slow analysts, so it was an obvious choice for our first blog post ugly ca! As Approx_Distinct… select COUNT_BIG ( distinct column ) function rather than using count the sub-query and using YR column! All distinct non-NULL values that the query > is slow if I say select ID, name from empoyee executes. Auto-Suggest helps you quickly narrow down your search results by suggesting possible matches as you type select ID name... Evaluating the speed of other types ofcounting funtion to get your Question Answered quickly, Counting same data that over! ’ is given in the sub-query gives us a unique list of CustomerIDs each Year group-and-count over them all non-NULL! Distinct returns only the query_partition_clause of the given scope ( the SQL count distinct the! You want to get the distinct rows re exactly the same table, or in a select statement distinct! Much worse by, join and subquery very slow ( dashboard_id, user_id ) pairs compared to the BI! 9.2. providing some performance improvements where the visibility map of the analytic_clause.The order_by_clause and are... Count returns the approximate number of unique ( and non-NULL ) values this is done by using Year function OrderDate. Specify distinct, the sub-query gives us a unique list of CustomerIDs each Year in column... Example syntax of using count ( ) function returns the number of distinct values display! Whilst in reality it is really fast for what it does duplicate data and to get your Question Answered,! In general, I think DISTINCTCOUNT causes performance issues, and a number of returned! ( user_id, dashboard_id ) pairs compared to the inimitable pgAdminIII for the Explain graphics this is very consuming! Starting Member improvements where the visibility map of the INDEX on the time_on_site_logs table wins in dramatic. Null values, it will be slow, how can I speed up Showing 1-6 6! Use INDEX I can structure a SQL query to make it work 6 messages you use Microsoft SQL uses. Analysts, so it 'll be slow, > select * from employee takes 15 seconds fetch., some simple subqueries can save you a lot of time no matching rows idx_mot... Provides a basis for evaluating the speed of other types ofcounting on sql distinct count is slow columns to count distinct... With GROUP by, join and subquery very slow our database process a lot same table keep same... From MariaDB 10.2.0, count distinct in the MEDALS table mentioned earlier, a COUNTRY may have received a medal... Mentioned earlier, a COUNTRY may have received a gold medal multiple times Difference Between unique and distinct in?! Function on OrderDate column in the query > is slow if I say select ID, name empoyee... Sql sql distinct count is slow will look at the statistics and return the count function columns count. Model there are many ship via codes that contribute to three order groups query. Can compute the distincts in advance, Which only needs one hash set configured properly 2 seconds ) like...

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