![]() ![]() ![]() Would the above approach work fast when there are say 100,000 records in the database? Would it not be better to have a [unique_constraint: (book_id, status:1) field in the records table indicating the active (or most recent row per book_id) and not to look for it by max(id). I have learned much about SQL and Ecto with this, yet at the same time I come to question the design of my tables. Where: books.institute_id = ^claims,īut your code looks nicer and possibly faster than the above. Left_join: records in subquery(records_query), Join: records in subquery(records_max_id_query), In the meantime, I had written a working code, like this: records_max_id_query = # started with the records table first. Despite that I did not express clearly what I was trying to achieve, you have grasped it and provided the needed solution. PostgreSQL GROUP Words cannot express how grateful I am to you. R in "records", d.book_id = r.book_id and d.record_id = r.id |> join(:left,, r in "records", b.id = r.book_id) You can view EDUCBA’s recommended articles for more information.I was to select from records the row with the highest id (newest in database) only for each book_id. ![]() We hope that this EDUCBA information on “PostgreSQL DISTINCT” was beneficial to you. We hope from the above article, you have understood how to use PostgreSQL SELECT DISTINCT statement to return unique rows by removing duplicate rows from the result set. We have defined an expression (s.department_id) for a DISTINCT ON clause to ORDER the result set in the above statement.JOIN departments d ON d.department_id = s.department_id Let’s look at the following statement, which joins student and department tables.Ĭode: SELECT DISTINCT ON (s.department_id) s.department_id, s.name, d.department_name INSERT INTO departments (department_id, department_name) VALUES INSERT INTO students (name, department_id) VALUES CREATE TABLE students (ĬONSTRAINT students_pk PRIMARY KEY (name) Let’s consider we have two tables named: students and departments. After the select list has been processed, the result table can optionally be subject to the elimination of duplicate rows. We should define the statement to get the sorted result set: remove all duplicate rows and keep a one-row entry for all. RED COLOR is present in both columns, back_color, and fore_color, in the ColorProperties table as we added back_color and fore_color with the DISTINCT clause, only one-row entry was kept for duplicate rows. The PostgreSQL statement will give us the unique values for both columns, back_color, and fore_color, from the ColorProperties table.As the SELECT DISTINCT clause contains back_color and fore_color, for removing the result’s duplicate rows, set the PostgreSQL combines values of both columns back_color and fore_color, etc.Let’s understand how to use the DISTINCT clause on multiple columns using the following statement: ![]() Also, to sort output results alphabetically, we will use the ORDER BY clause for the values in the fore_color column. We will use the following statement to fetch the unique values of the column named fore_color. Output: After executing the above statement, we will follow the result.
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