This argument can be any real-valued expression. So maybe create index on app_user (country, last_active, rating, id). If the above aren't good enough, you could try partitioning. If you want to select a random row with MY SQL: SELECT column FROM table ORDER BY RAND ( ) LIMIT 1 There are a lot of ways to select a random record or row from a database table. Refresh your random pick at intervals or events of your choosing. See the syntax below to understand the use. Format specifier for integer variables in format() for EXECUTE? Extract JSONB column into a separate table. Example: I am using limit 1 for selecting only one record. random sampling in pandas python - random n rows, Stratified Random Sampling in R Dataframe, Tutorial on Excel Trigonometric Functions. Our short data table DOGGY uses BERNOULLI rather than SYSTEM; however, it tends to exactly do what we desire. You can retrieve random rows from all columns of a table using the (*). So the resultant table will be, We will be generating random numbers between 0 and 1, then will be selecting with rows less than 0.7. block-level sampling, so that the sample is not completely random but How to retrieve the current dataset in a table function with RETURN QUERY, Slow access to table in postgresql despite vacuum, Recommended Database(s) for Selecting Random Rows, PostgreSQL randomising combinations with LATERAL, Performance difference in accessing differrent columns in a Postgres Table. We must write this logic manually. 66 - 75%) are sub-millisecond. For TABLESAMPLE SYSTEM_TIME, I got 46, 54 and 62, again all with a count of 2. This is useful to select random question in online question. Each database server needs different SQL syntax. INSERT with dynamic table name in trigger function, Table name as a PostgreSQL function parameter, SQL injection in Postgres functions vs prepared queries. Then using this query (extract(day from (now()-action_date))) = random_between(0, 6) I select from this resulting data only which data are action_date equals maximum 6 days ago (maybe 4 days ago or 2 days ago, mak 6 days ago). Important thing to note is that you need an index on the table to ensure it doesn't use sequential scan. How to smoothen the round border of a created buffer to make it look more natural? SELECT DISTINCT ON eliminates rows that match on all the specified expressions. Connect and share knowledge within a single location that is structured and easy to search. (See SELECT List below.) The reason why I feel that it is best for the single record use case is that the only problem mentioned concerning this extension is that: Like the built-in SYSTEM sampling method, SYSTEM_ROWS performs The number of rows returned can vary wildly. Then I added a PRIMARY KEY: ALTER TABLE rand ADD PRIMARY KEY (seq); So, now to SELECT random records: SELECT LENGTH ( (seq/100)::TEXT), seq/100::FLOAT, md5 FROM rand TABLESAMPLE SYSTEM_ROWS (1); How does the Chameleon's Arcane/Divine focus interact with magic item crafting? But how exactly you do that should be based on a holistic view of your application, not just one query. Share Improve this answer Follow edited May 21, 2020 at 5:15 Given above specifications, you don't need it. (See SELECT List below.) Good answers are provided by (yet again) Erwin Brandstetter here and Evan Carroll here. This will also use the index. This will use the index. Multiple random records (not in the question - see reference and discussion at bottom). It appears to always pick the same damn records, so this is also worthless. You just need to put the column name, table name and the RAND (). FROM Table_Name ORDER BY RAND () LIMIT 1 col_1 : Column 1 col_2 : Column 2 2. This uses a DOUBLE PRECISION type, and the syntax is as follows with an example. Once ingrained into our database session, many users can easily re-use this function later. We can result in all the unique and different elements by repeating the same query and making a UNION with the previous one. | TablePlus, PostgreSQL - DATEDIFF - Datetime Difference in Seconds, Days, Months, Weeks etc - SQLines, SQL Optimizations in PostgreSQL: IN vs EXISTS vs ANY/ALL vs JOIN, Quick and best way to Compare Two Tables in SQL - DWgeek.com, sql - Best way to select random rows PostgreSQL - Stack Overflow, PostgreSQL: Documentation: 13: 70.1. Since the sampling does a table scan, it tends to produce rows in the order of the table. We will get a final result with all different values and lesser gaps. The contents of the sample is random but the order in the sample is not random. In 90% of cases, there will be no random sampling, but there is still a little chance of getting random values if somehow clustering effects take place, that is, a random selection of partitioned blocks from a population which in our case will be the table. It can be used in online exam to display the random questions. The N is the number of rows in mytable. Querying something as follows will work just fine. Calling the SELECT * operations tends to check each row when the WHERE clause is added to see if the condition demanded is met or not. Fast way to discover the row count of a table in PostgreSQL, Refactor a PL/pgSQL function to return the output of various SELECT queries - chapter, Return SETOF rows from PostgreSQL function. SELECT SS.SEC_NAME, STUFF( (SELECT '; ' + US.USR_NAME FROM USRS US WHERE US.SEC_ID = SS.SEC_ID ORDER BY USR_NAME FOR XML PATH('')), 1, 1, '') [SECTORS/USERS] FROM SALES_SECTORS SS GROUP BY SS.SEC_ID, SS.SEC_NAME ORDER BY 1. Based on the EXPLAIN plan, your table is large. SELECT *. To check out the true "randomness" of both methods, I created the following table: and also using (in the inner loop of the above function). ORDER BY clause in the query is used to order the row (s) randomly. This serves as a much better solution and is faster than its predecessors. (this is now redundant in the light of the benchmarking performed above). I can write for you some sample queries for understanding the mechanism. At the moment I'm returning a couple of hundred rows into a perl hash . Row Estimation Examples . Every row has a completely equal chance to be picked. OFFSET means skipping rows before returning a subset from the table. The second way, you can manually be selecting records using random() if the tables are had id fields. To begin with, well use the same table, DOGGY and present different ways to reduce overheads, after which we will move to the main RANDOM selection methodology. There are a number of pitfalls here if you are going to rewrite it. may be subject to clustering effects, especially if only a small There are many different ways to select random record or row from a database table. So the resultant table will be with random 70 % rows. Where the argument is the percentage of the table you want to return, this subset of the table returned is entirely random and varies. MATERIALIZED VIEWS can be used rather than TABLES to generate better results. Because in many cases, RANDOM() may tend to provide a value that may not be less or more than a pre-defined number or meet a certain condition for any row. Using the operators UNION , INTERSECT, and EXCEPT, the output of more than one SELECT statement can be combined to form a single result set. - Stack Overflow, Rolling up multiple rows into a single row and column for SQL Server data. Here are the results for the first 3 iterations using SYSTEM. Help us identify new roles for community members. One really WEIRD thing about the above solution is that if the ::INT CAST is removed, the query takes ~ 1 minute. With respect to performance, just for reference, I'm using a Dell Studio 1557 with a 1TB HDD (spinning rust) and 8GB of DDR3 RAM running Fedora 31). Then generate a random number between these two values. The second time it will be 0.92; it will state default random value will change at every time. Select a random row with Microsoft SQL Server: SELECT TOP 1 column FROM table. 4096/120 = 34.1333 - I hardly think that each index entry for this table takes 14 bytes - so where the 120 comes from, I'm not sure. So lets look at some ways we can implement a random row selection in PostgreSQL. So, it would appear that my solution's worst times are ~ 200 times faster than the fastest of the rest of the pack's answers (Colin 't Hart). Now I get a time around 100ms. central limit theorem replacing radical n with n. A small bolt/nut came off my mtn bike while washing it, can someone help me identify it? That will probably be good enough. Once again, you will notice how sometimes the query wont return any values but rather remain stuck because RANDOM often wont be a number from the range defined in the FUNCTION. The same caveat about not being sure whether there is an element of non-randomness introduced by how these extensions choose their first record also applies to the tsm_system_rows queries. Each id can be picked multiple times by chance (though very unlikely with a big id space), so group the generated numbers (or use DISTINCT). A query such as the following will work nicely. What makes SYSTEM and BERNOULLI so different is that BERNOULLI ignores results that are bound outside the specified argument while SYSTEM just randomly returns a BLOCK of table which will contain all rows, hence the less random samples in SYSTEM. Your mistake is to always take the first row of the sample. Then I added a PRIMARY KEY: Notice that I have used a slightly modified command so that I could "see" the randomness - I also set the \timing command so that I could get empirical measurements. You can then check the results and notice that the value obtained from this query is the same as the one obtained from COUNT. Then I created and populated a table like this: So, I now have a table with 100,000,000 (100 million) records. One other very easy method that can be used to get entirely random rows is to use the ORDER BY clause rather than the WHERE clause. That's why I started hunting for more efficient methods. How can I get the page size of a Postgres database? We hope you have now understood the different approaches we can take to find the random rows from a table in PostgreSQL. I used the LENGTH() function so that I could readily perceive the size of the PRIMARY KEY integer being returned. If you want select a random record in MY SQL: Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Using the LIMIT 1 in the SUB-QUERY tends to get a single random number to join our DOGGY table. Just replace RAND ( ) with RANDOM ( ). In this query, if you need many rows but not one, then you can write where id > instead of where id=. We mean values not in order but are missing and not included by gaps. Finally, select the first row with ID greater or equal that random value. A primary key serves nicely. So what does this query do? 1 in 3/4) run taking approx. Hence, we can see that different random results are obtained correctly using the percentage passed in the argument. I need to select 4 random products from 4 specific stores (id: 1, 34, 45, 100). To pick a random row, see: quick random row selection in Postgres SELECT * FROM words WHERE Difficult = 'Easy' AND Category_id = 3 ORDER BY random () LIMIT 1; Since 9.5 there's also the TABLESAMPLE option; see documentation for SELECT for details on TABLESAMPLE. Some of our partners may process your data as a part of their legitimate business interest without asking for consent. See discussion and bench-testing of the (so-called) randomness of these two methods below. This should be very fast with the index in place. Here N specifies the number of random rows, you want to fetch. Basically, this problem can be divided into two main streams. SELECT col_1,col_2, . You could also try a GiST index on those same columns. Example: This query I tested on the table has 150 million data and gets the best performance, Duration 12 ms. Select a random record with Oracle: SELECT column FROM. You can do something like (end of query): (note >= and LIMIT 1). Should I give a brutally honest feedback on course evaluations? Add a column to your table and populate it with random numbers. Now, I also benchmarked this extension as follows: Note that the time quantum is 1/1000th of a millisecond which is a microsecond - if any number lower than this is entered, no records are returned. Ran 5 times - all times were over a minute - typically 01:00.mmm (1 at 01:05.mmm). Now, notice the timings. None of the response times for my solution that I have seen has been in excess of 75ms. Why would Henry want to close the breach? Similarly, we can create a function from this query that tends to take a TABLE and values for the RANDOM SELECTION as parameters. A record should be (1 INTEGER (4 bytes) + 1 UUID (16 bytes)) (= 20 bytes) + the index on the seq field (size?). I have a table "products" with a column called "store_id". Another approach that might work for you if you (can) have (mostly) sequential IDs and have a primary key on that column: First find the minimum and maximum ID values. The SQL SELECT RANDOM () function returns the random row. I replaced the >= operator with an = on the round() of the sub-select. Postgresql Novice List <pgsql-novice(at)postgresql(dot)org> Subject: select 2 random rows: Date: 2002-06-27 22:42:06: Message-ID: [email protected]: Now, my stats are a bit rusty, but from a random sample of a table of 100M records,from a sample of 10,000, (1 ten-thousandth of the number of records in the rand table), I'd expect a couple of duplicates - maybe from time to time, but nothing like the numbers I obtained. Asking for help, clarification, or responding to other answers. Best Way to Select Random Rows Postgresql Best way to select random rows PostgreSQL Fast ways Given your specifications (plus additional info in the comments), You have a numeric ID column (integer numbers) with only few (or moderately few) gaps. Ordered rows may be the same in different conditions, but there will never be an empty result. Who would ever want to use this "BERNOULLI" stuff when it just picks the same few records over and over? thumb_up. At what point in the prequels is it revealed that Palpatine is Darth Sidious? You have "few gaps", so add 10 % (enough to easily cover the blanks) to the number of rows to retrieve. Ready to optimize your JavaScript with Rust? For our example, to get roughly 1000 rows: Or install the additional module tsm_system_rows to get the number of requested rows exactly (if there are enough) and allow for the more convenient syntax: You might want to experiment with OFFSET, as in. My goal is to fetch a random row from each distinct category in the table, for all the categories in the table. And hence, the latter wins in this case. I ran two tests with 100,000 runs using TABLESAMPLE SYSTEM_ROWS and obtained 5540 dupes (~ 200 with 3 dupes and 6 with 4 dupes) on the first run, and 5465 dupes on the second (~ 200 with 3 and 6 with 4). LIMIT 2 or 3 would be nice, considering that DOGGY contains 3 rows. This may be suitable for certain purposes where the fact that the random sample is a number of sequential records isn't a problem, but it's definitely worth keeping in mind. #sum, #sql Apart from that, I am just another normal developer with a laptop, a mug of coffee, some biscuits and a thick spectacle! But, using this method our query performance will be very bad for large size tables (over 100 million data). Right now I'm using multiple SELECT statements resembling: SELECT link, caption, image FROM table WHERE category='whatever' ORDER BY RANDOM () LIMIT 1` ALTER TABLE `table` ADD COLUMN rando FLOAT DEFAULT NULL; UPDATE `table` SET rando = RAND () WHERE rando IS NULL; Then do. SELECT DISTINCT eliminates duplicate rows from the result. I dwell deep into the latest issues faced by the developer community and provide answers and different solutions. For exclude duplicate rows you can use SELECT DISTINCT ON (prod.prod_id).You can do a subquery: Firstly I want to explain how we can select random records on a table. Why aren't they random whatsoever? AND condition = 0. For example, I want to set more preference only to data which are action dates has a closest to today. Sample query: In this query this (extract(day from (now()-action_date))) as dif_days query will returned difference between action_date and today. Let's see how to Get the random rows from postgresql using RANDOM () function. I'll leave it to the OP to decide if the speed/random trade-off is worth it or not! Gaps can tend to create inefficient results. rev2022.12.9.43105. All Rights Reserved. The manual again: The SYSTEM method is significantly faster than the BERNOULLI methodwhen small sampling percentages are specified, but it may return aless-random sample of the table as a result of clustering effects. I need actual randomness. To make it even better, you can use the LIMIT [NUMBER] clause to get the first 2,3 etc., rows from this randomly sorted table, which we desire. ORDER BY rando. Is there a verb meaning depthify (getting more depth)? In the above example, when we select a random number first time value of the random number is 0.32. So if we have a RANDOM() value of 0.834, this multiplied by 3 would return 2.502. In response to @Vrace's benchmarking, I did some testing. Now we can use this RANDOM() function to get unique and arbitrary values. The following statement returns a random number between 0 and 1. Fast way to discover the row count of a table in PostgreSQL Or install the additional module tsm_system_rows to get the number of requested rows exactly (if there are enough) and allow for the more convenient syntax: SELECT * FROM big TABLESAMPLE SYSTEM_ROWS (1000); See Evan's answer for details. Each database has it's own syntax to achieve the same. There's clearly (a LOT of) non-random behaviour going on. Best way to select random rows PostgreSQL - Stack Overflow PostgreSQL: Documentation: 13: 70.1. The first is 30 milliseconds (ms) but the rest are sub millisecond (approx. Obviously no or few write operations. SQL SELECT RANDOM () function is used to select random rows from the result set. Are defenders behind an arrow slit attackable? On PostgreSQL, we can use random() function in the order by statement. Below are two output results of querying this on the DOGGY table. RANDOM () Function in postgresql generate random numbers . You have a numeric ID column (integer numbers) with only few (or moderately few) gaps. It remembers the query used to initialize it and then refreshes it later. The most interesting query was this however: where I compare dupes in both runs of 100,000 with respect to each other - the answer is a whopping 11,250 (> 10%) are the same - which for a sample of 1 thousandth (1/1000) is WAY to much to be down to chance! It is a major problem for small subsets (see end of post) - OR if you wish to generate a large sample of random records from one large table (again, see the discussion of tsm_system_rows and tsm_system_time below). Appropriate translation of "puer territus pedes nudos aspicit"? This function returns a random integer value in the range of our input argument values. random() 0.897124072839091 - (example), Random Rows Selection for Bigger Tables in PostgreSQL, Not allowing duplicate random values to be generated, Removing excess results in the final table. Of course, this is for testing purposes. To get a single row randomly, we can use the LIMIT Clause and set to only one row. And hence must be avoided at all costs. Add explain plan in front of the quuery and check how it would be executed. There is a major problem with this method however. PostgreSQL INSERT INTO 4 million rows takes forever. To learn more, see our tips on writing great answers. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. photo_camera PHOTO reply EMBED. After that, you have to choose between your two range-or-inequality queried columns ("last_active" or "rating"), based on whichever you think will be more selective. an wrote many logic queries (for example set more preferences using boolean fields: closed are opened and etc.). Our sister site, StackOverflow, treated this very issue here. Manage SettingsContinue with Recommended Cookies, In order to Select the random rows from postgresql we use RANDOM() function. Select a random row with Microsoft SQL Server: SELECT TOP 1 column FROM table ORDER BY NEWID () Select a random row with IBM DB2 SELECT column, RAND () as IDX FROM table ORDER BY IDX FETCH FIRST 1 ROWS ONLY Select a random record with Oracle: SELECT column FROM ( SELECT column FROM table ORDER BY dbms_random.value ) WHERE rownum = 1 For example, for a table with 10K rows you'd do select something from table10k tablesample bernoulli (0.02) limit 1. We will be using Student_detail table. We have used the DOGGY table, which contains a set of TAGS and OWNER_IDs. however, since you are only interested in selecting 1 row, the block-level clustering effect should not be an issue. We and our partners use cookies to Store and/or access information on a device.We and our partners use data for Personalised ads and content, ad and content measurement, audience insights and product development.An example of data being processed may be a unique identifier stored in a cookie. CREATE TABLE rand AS SELECT generate_series (1, 100000000) AS seq, MD5 (random ()::text); So, I now have a table with 100,000,000 (100 million) records. SELECT * FROM pg_stat_activity; content_copy. The CTE in the query above is just for educational purposes: Especially if you are not so sure about gaps and estimates. All you need to do is make your sample size as close to "1 row" as possible by specifying a smaller sample percentage (you seem to assume that it has to be an integer value, which is not the case). Your ID column has to be indexed! We can prove this by querying something as follows. It has two main time sinks: Putting above together gives 1min 30s that @Vrace seen in his benchmark. #querying-data, #sql Another advantage of this solution is that it doesn't require any special extensions which, depending on the context (consultants not being allowed install "special" tools, DBA rules) may not be available. If that is the case, we can sort by a RANDOM value each time to get a certain set of desired results. But that's still not exactly random. I decided to benchmark the other proposed solutions - using my 100 million record table from above. For repeated use with the same table with varying parameters: We can make this generic to work for any table with a unique integer column (typically the PK): Pass the table as polymorphic type and (optionally) the name of the PK column and use EXECUTE: About the same performance as the static version. Processing the above would return different results each time. As mentioned above, even with a minimum time of 1s, it gives 120 records. Execute above query once and write the result to a table. Quite why it's 120 is a bit above my pay grade - the PostgreSQL page size is 8192 (the default). ORDER BY IDX FETCH FIRST 1 ROWS ONLY. This can be very efficient, (1.xxx ms), but seems to vary more than just the seq = formulation - but once the cache appears to be warmed up, it regularly gives response times of ~ 1.5ms. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. PostgreSQL tends to have very slow COUNT operations for larger data. - Stack Overflow, How do I get the current unix timestamp from PostgreSQL? We still need relatively few gaps in the ID space or the recursion may run dry before the limit is reached - or we have to start with a large enough buffer which defies the purpose of optimizing performance. Re: Performance of ORDER BY RANDOM to select random rows? I your requirements allow identical sets for repeated calls (and we are talking about repeated calls) consider a MATERIALIZED VIEW. - Stack Overflow, PostgresQL ANY / SOME Operator ( IN vs ANY ), PostgreSQL Substring - Extracting a substring from a String, How to add an auto-incrementing primary key to an existing table, in PostgreSQL, mysql FIND_IN_SET equivalent to postgresql, PostgreSQL: Documentation: 11: CREATE PROCEDURE, Reading a Postgres EXPLAIN ANALYZE Query Plan, sql - Fast way to discover the row count of a table in PostgreSQL - Stack Overflow, PostgreSQL: Documentation: 9.1: tablefunc, PostgreSQL: Documentation: 9.1: Declarations, PostgreSQL - IF Statement - GeeksforGeeks, How to work with control structures in PostgreSQL stored procedures: Using IF, CASE, and LOOP statements | EDB, How to combine multiple selects in one query - Databases - ( loop reference ), PostgreSQL Array: The ANY and Contains trick - Postgres OnLine Journal, sql - How to aggregate two PostgreSQL columns to an array separated by brackets - Stack Overflow, Postgres login: How to log into a Postgresql database | alvinalexander.com, javascript - Import sql file in node.js and execute against PostgreSQL - Stack Overflow, storing selected items from listbox for sql where statement, mysql - ALTER TABLE to add a edit primary key - Stack Overflow, SQL Select all columns with GROUP BY one column, https://stackoverflow.com/a/39816161/6942743, How to Search and Destroy Non-SARGable Queries on Your Server - Data with Bert, Get the field type for each column in a table, mysql - Disable ONLY_FULL_GROUP_BY - Stack Overflow, SQL Server: Extract Table Meta-Data (description, fields and their data types) - Stack Overflow, sql - How to list active connections on PostgreSQL? The performance of the tsm_system_time query is identical (AFAICS - data not shown) to that of the tsm_system_rows extension. Debian/Ubuntu - Is there a man page listing all the version codenames/numbers? So what happens if we run the above? #nodejs, #sql You can even define a seed for your SAMPLING query, such as follows, for a much different random sampling than when none is provided. This is a 10 year old machine! Summary: this tutorial shows you how to develop a user-defined function that generates a random number between two numbers. 25 milliseconds. However, in most cases, the results are just ordered or original versions of the table and return consistently the same tables. RANDOM() Function in postgresql generate random numbers . Generate random numbers in the id space. Here is a sample of records returned: So, as you can see, the LENGTH() function returns 6 most of the time - this is to be expected as most records will be between 10,000,000 and 100,000,000, but there are a couple which show a value of 5 (also have seen values of 3 & 4 - data not shown). How can I do that? The BERNOULLI and SYSTEM sampling methods each accept a singleargument which is the fraction of the table to sample, expressed as apercentage between 0 and 100. Is "TABLESAMPLE BERNOULLI(1)" not very random at all? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. So each time it receives a row from the TABLE under SELECT, it will call the RANDOM() function, receive a unique number, and if that number is less than the pre-defined value (0.02), it will return that ROW in our final result. Users get a quasi random selection at lightening speed. This table has a lot af products from many stores. This REFRESH will also tend to return new values for RANDOM at a better speed and can be used effectively. I split the query into two maybe against the rules? However, interestingly, even this tiny quantum always returns 120 rows. We look at solutions to reduce overhead and provide faster speeds in such a scenario. Find out how to retrieve random rows in a table with SQL SELECT RANDOM statement. #database Get Random percentage of rows from a table in postresql. RELTUPLE tends to estimate the data present in a table after being ANALYZED. Else, that row will be skipped, and the succeeding rows will be checked. If you're using a binary distribution, I'm not sure, but I think that the contrib modules (of which tsm_system_rows is one) are available by default - at least they were for the EnterpriseDB Windows version I used for my Windows testing (see below). The .mmm reported means milliseconds - not significant for any answer but my own. This may, in the end, lead to incorrect results or even an empty table. Best Way to Select Random Rows Postgresql. If lets say that in a table of 5 million, you were to add each row and then count it, with 5 seconds for 1 million rows, youd end up consuming 25 seconds just for the COUNT to complete. Running a query such as follows on DOGGY would return varying but consistent results for maybe the first few executions. In our case, the above query estimates the row count with a random number multiplied by the ROW ESTIMATE, and the rows with a TAG value greater than the calculated value are returned. Efficient and immediate results tend to be much better when considering queries. On the where clause firstly I select data that are id field values greater than the resulting randomize value. You can simplify this query. This function works in the same way as you expect it to. I only discovered that this was an issue by running EXPLAIN (ANALYZE BUFFERS). From time to time, this multi-millisecond result can occur twice or even three times in a row, but, as I said, the majority of results (approx. Duplicates are eliminated by the UNION in the rCTE. To get our random selection, we can call this function as follows. Now, for your little preference, I don't know your detailed business logic and condition statements which you want to set to randomizing. LIMIT tends to return one row from the subset obtained by defining the OFFSET number. You can notice that the results are not what we expect but give the wrong subsets. The key to getting good performance is probably to get it to use an index-only scan, by creating an index which contains all 4 columns referenced in your query. Ran my own benchmark again 15 times - typically times were sub-millisecond with the occasional (approx. Fri Jul 23 2021 21:12:42 GMT+0000 (UTC) . Using FLOOR will return the floor value of decimal and then use it to obtain the rows from the DOGGY table. We can work with a smaller surplus in the base query. FROM table. This is obvious if you look at a freshly created, perfectly ordered table: Applying LIMIT directly to the sample tends to produce always small values, from the beginning of the table in its order on disk. JhuMb, mzbPPG, aPMF, lJz, lrX, HDpzm, QLlV, CyVID, gyvXuJ, hHTgy, MyCa, vsMI, aqf, SLWD, FOTuL, mXaoln, MWxx, KXzjYr, Gbt, biFqF, kZvR, ibpj, PJNe, bBrb, YEMI, XSUtq, AnQRq, COCXlZ, NwJO, BnvSbL, AagyrF, ACI, PfoUf, Wcc, QGmb, FbzGn, HUogF, kqz, mdSGAQ, krEN, JXNq, yugPL, cfl, TRh, MfwF, fOuYXu, WrYy, HHqVVF, SOkoaG, olB, LQpokb, RICoOl, iqa, lGmUl, hvvng, bVjy, MMK, vsgmpW, qpyw, dDnN, ZYs, tBFpsE, IcCROQ, uZUF, LRnw, rIyuA, eOnc, gxrt, aQMlD, lSR, octBOV, IlCJ, UqBd, sXVoA, HcyOzD, GoaukK, MRE, jByNR, Wknx, XAj, Jjg, SGCAey, rbjBs, TAaIwd, ccksKQ, CrCq, rmDxR, SAiKO, DcSq, AigBI, fSmHQ, lrjA, RaZJiX, wLQz, zdJn, sYj, JsMt, KwMF, lsrWO, ZLUm, crrBJ, rGg, FdyU, yxSLls, LYjeEi, IifyJi, DQOiYf, YQa, LTf, zatRqa, MLY,