Questions tagged [distinct]

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23
votes
5answers
82k views

SELECT DISTINCT on multiple columns

Supposing we have a table with four columns (a,b,c,d) of the same data type. Is it possible to select all distinct values within the data in the columns and return them as a single column or do I ...
7
votes
2answers
10k views

Get the last 5 distinct values for each ID

I'm working with PostgreSQL 9.4. I have a table that contains the following entries: id | postcode | date_created ---+----------+----------------- 14 | al2 2qp | 2015-09-23 14:46:57 14 | al2 ...
5
votes
1answer
988 views

Fastest query for distinct IDs in a many-to-many relationship

I have this table in PostgreSQL 9.4: CREATE TABLE user_operations( id SERIAL PRIMARY KEY, operation_id integer, user_id integer ) The table consists of ~1000-2000 different operations ...
2
votes
0answers
55 views

Oracle DISTINCT with NULLable columns

There is a longstanding(?) problem(?) with Oracle that if you want to use a DISTINCT select on a column which has a B*-Tree Index but is nullable, that the index is not used. (As other answers suggest,...
1
vote
1answer
39 views

Query to partially summarize data in a table using SQL

I'm learning how to handle databases, so this is a trivial question, and quite likely has been answered already. I'm just not familiar to the lingo and have no idea how to search for it (although I ...
1
vote
1answer
141 views

Improving distinct values estimates in Postgres

Full counts in Postgres can be slow, for reasons that are well-understood and much discussed. So, I've been using estimation techniques instead, where possible. For rows, pg_stats seems fine, for ...
0
votes
0answers
110 views

Retrieving a record for the last date received and returning the value of another column in that row

I have the following query which is returning me total number of expected records : select a.New_FirstName + ' ' + a.New_LastName as 'Account Name', a.New_MPRNNumber,MAX(b.New_readdate) as 'Last SC ...