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distinct 전체검색 결과
- 게시판 2개
- 게시물 7개
- 1/1 페이지 열람 중
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drop table if exists x;
drop table if exists y;
CREATE TABLE x
(
x TEXT ,
CONSTRAINT uq_x UNIQUE (x)
);
-- unique 로 선언되었지만 null 값은 예외입니다. 중복으로 insert 가 가능합니다.
insert into x values(null);
insert into x values(null);;
select * From x;
x
--------
<NULL>
<NULL>
---------------…
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scott@[local]:5432:scottdb]
SQL> create table test(x varchar(20), y int);
scott@[local]:5432:scottdb]
SQL> insert into test values('lion',2);
INSERT 0 1
scott@[local]:5432:scottdb]
SQL> insert into test values('lion',1);
INSERT 0 1
scott@[local]:5432:scottdb]
SQL> insert into test values…
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Two years ago, I had written a note saying that you should avoid using DISTINCT ON when query performance is essential:https://www.postgresdba.com/bbs/board.php?bo_table=C05&wr_id=106&page=6Regrettably, it turns out that my statement was incorrect. During an experiment on retrieving the most…
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I am currently working on a project that involves transforming Oracle SQL statements into equivlanet PostgreSQL statements. During my work, I noticed a significant peformance degradation after running a query with the DISTINCT keyword in PostgreSQL.Writing efficient and optimzed SQL queries requires…
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In the previous article I
have taken advantage of the technique of extracting distinct values from
an indexed column efficiently. The technique is so commonly used that
many blog posts have introduced it. According to Jonathan Lewis, Sayan
Malakshnov,a Russian, was one of those …
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From time to time when I cannot find a solution to speed up a query, I google a solution. In most cases, someone has already posted the answer.
The tuning technique presented in this note was derived from the article below.
https://scidb.tistory.com/entry/COUNTDistinct-%EC%BB%AC%EB%9F%BC%EC%9D%98-%…
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distinct on 절은 표준SQL은 아니고, PostgreSQL에서만 사용할 수 있는 문법이다.
SQL 튜닝 중에 distinct on 절을 사용해 보았으나, 속도가 더 느려져서 분석 내용을 공유한다.
결론부터 얘기하자면, distinct on 절 대신에 표준 SQL 문법을 사용하라.
SALES 테이블 구조
CREATE TABLE sales (
sale_id NUMERIC NOT NULL,
employee_id NUMERIC NOT NULL,
subsidiary_id NUMERIC NOT NULL,
sale_dat…
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