Questions tagged [union]

Combines two or more query results. UNION removes duplicates; UNION ALL retains all rows.

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2answers
18 views

Select next or first row

For a given ID, I'm trying to get the next row or if not present (end of list), return the first one. ID (primary key) value 1 John 3 Bob 9 ...
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1answer
19 views

is it relatively safe to union two tables with UUID PK? [closed]

I want to union two tables whose primary keys are UUID(V4) and I want to preserve them in the result. I work with PostgreSQL Is it safe to do this? What are the pitfalls may be encountered?
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1answer
27 views

Combine two union all using group by and 2 limit row for each group id [closed]

I need to use a faster and better performance query than the one below: (SELECT * FROM ((SELECT * FROM index_trade_summaries WHERE index_id = 1) UNION ALL (SELECT * FROM ...
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2answers
57 views

Get rows above and below a certain row, based on two criteria SQL (with SUM)

Say I have a table like so: +----------+---------+------+---------------------+ |student_no|level_id |points| timestamp | +----------+---------+------+---------------------+ | 4 | ...
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2answers
61 views

Get rows above and below (neighbouring rows) a certain row, based on two criteria SQL

Say I have a table like so: +---+-------+------+---------------------+ |id | level |score | timestamp | +---+-------+------+---------------------+ | 4 | 1 | 70 | 2021-01-14 21:50:38 | |...
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3answers
39 views

Understanding comparison operators on columns

Consider this dummy_data: number 1 2 3 4 5 I want to return all the rows from dummy_data where column number is below a certain value. Came up with this: WITH dummy_data AS ( (SELECT 1 ...
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2answers
28 views

Why MySQL doesn't use indexes in view with union select?

I've created a view: create view dh_hits_new_all_old as select * from dh_hits_new_201806 union all select * from dh_hits_new_201807; When I select something with a where clause containing a field ...
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1answer
41 views

What does UNION do? Difference between Union and Union ALL? [closed]

I need some help to understand this question with some examples please never done them before in database. What does UNION do? Difference between Union and Union All?
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1answer
66 views

T-SQL equivalent to Python Pandas Concatenate

I have a few tables that I would like to merge in a similar way that Python Pandas Concatenate does. I do not want to replicate the information for it is rather large. I'd like to have a VIEW like ...
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2answers
32 views

How to combine multiple EXEC statements into a single SELECT?

I run this every month to extract database logs, and I have to change the dates as well. DECLARE @start DATETIME SET @start = CONVERT(DATETIME, '2020-08-01 00:00'); DECLARE @end DATETIME SET @end = ...
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4answers
189 views

Get results from “combined, either inner join”

I have a feeling this must have been asked multiple times, but I just cannot find a solution, or even a questions probably because of difficulty in explaining. We all know that inner join basically ...
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1answer
68 views

Why does Type Resolution fail when using SELECT DISTINCT instead of SELECT on PostgreSQL?

Here is a minimal reproduction: SELECT 1 UNION ALL SELECT DISTINCT NULL Fails with: UNION types numeric and text cannot be matched According to the PostgreSQL documentation on Type Resolution for ...
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2answers
27 views

How to order some rows one way, and the rest another way?

I am trying to sort rows from a table in PostgreSQL 10.12: CREATE TABLE example ( id serial PRIMARY KEY, val text NOT NULL, x integer NOT NULL, y integer NOT NULL ); INSERT INTO example (...
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0answers
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Select Type UNION RESULT doesn't appear in the output of Explain statement

EXPLAIN SELECT actor_id, (SELECT 1 FROM sakila.film_actor WHERE film_actor.actor_id = der_1.actor_id LIMIT 1) FROM ( SELECT actor_id FROM sakila.actor LIMIT 5 ) AS der_1 UNION ALL SELECT film_id, (...
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0answers
20 views

Save multiple dynamic filter for aggregation in Postgresql

What is the most efficient way to store multiple dynamic filters which can be created by users on given data and us the filter for aggregating data? Lets assume I have a table called t_filter which ...
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0answers
15 views

Single table with many null fields or two tables used with union? [duplicate]

I am designing database for my small project and I've hit a "good design practice" wall ;) I need to add records that will have one of two structures, containing different set of information (10-20 ...
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1answer
65 views

Select from other table if exist

hi I want to union 2 tables but I am not sure if the table is exits this is my query: select a from table union select case when exists(select a from table1) then (select a from table1) else (...
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1answer
576 views

Subqueries for JSON path where outer query is part of a UNION result in strings rather than JSON

Bear with me - the example code has bit going on and I'll do my best to explain it, below. with ENTITIES as ( select [name] as entityName from (values ('A'), ('B'), ('C')) X([name]) ), PROPERTIES as ( ...
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1answer
101 views

JOIN/Union Two tables, removing NULL where possible (similar to pandas concatenate)

I am wondering how to perform an operation that I guess is most akin to a concatenate if you're familiar with pandas. Basically, what I want to do seems like a UNION where records are "collapsed" in ...
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2answers
133 views

Union probably not right for this [closed]

I have a table witrh 3 columns: id price created_at 1 0 ts 2 5 ts 3 0 ts 4 3 ts I'd like to have a result table that contains 2 rows, like this: id ...
1
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1answer
27 views

Caching derived dataset automatically in SQL Server

I have a view that combines multiple tables via UNION ALL, and handles some basic errors with the data. Due to the way that the errors are handled, the view is a bit slower than I would hope. Is there ...
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0answers
31 views

Why does UNION fail here?

I have a problem that I can't seem to figure out how to fix. What I want to do is simple, select data and append a row of sums as the last row. But I keep getting the error An error occurred in ...
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1answer
43 views

How do I join on a timestamp and include NULL entries?

I am attempting a query to compare the sum of daily accounting invoices to a daily budget. The budget is stored as one value for a month, so I divide that amount by the total number of days as in ...
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0answers
29 views

SQL Server - is there a way to convert OR conditions to UNION to improve performance (as part of execution plan, under the hood)? [duplicate]

Let's assume we have following query (greatly simplified, of course): SELECT * FROM MyTable Where A or B The query takes about 30 seconds to run When I rewrite the query as SELECT DISTINCT * FROM ...
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1answer
192 views

Bag union operation in relational algebra

I have difficulty in understanding how does the bag union operates in relational algebra? Here, 1) has a schema (X, Y, A) 2) (Y, A) 3) (X, A) 4) (Y, A) so how will output look like after union ...
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1answer
28 views

MySQL COUNT based on a condition [duplicate]

I have a MariaDB database, in which I have this table: ID | Item Name | Item replaced | ----------------------------------------- 0 | Item 1 | Replaced 1 | Item 2 | 2 | Item 3 | ...
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2answers
263 views

Microsoft SQL Server 2014 Nested From Query in Cross-Apply

When selecting from a nested query in an OUTER APPLY statement the nested query seems to be evaluated only once in certain circumstances. Bug reported to Azure Feedback Forum: https://feedback.azure....
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2answers
309 views

Alternative to slow [LEFT JOIN + OR] without UNION?

I have a reasonably simple query that returns all purchases for a given user, searching by his government issued id. The document could be in two different tables. The query using only left joins ...
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3answers
2k views

UNION queries with different number of columns?

I have 2 queries on a table: SELECT *, 1 as query_cr_0 FROM invoices LEFT OUTER JOIN customers ON customers.id = invoices.customer_id WHERE (customers.id IN (64, 66, 63, 62, 65)) SELECT *, 5 as ...
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1answer
117 views

Union from Multiple Tables in many databases and group results in batches of n

First post in dba, so please be gentle. I have a project I am working through and have 4+ SQL Server databases to work with. These DBs contain 2 (or more tables) I wish to UNION the results from. ...
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1answer
41 views

SQL db query using UNION and Left Join

I have 6 tables (t1, t2, t3, ...,t6 in the same SQL Server 2008 R2 database. I wanted to group them into two. Group 1 (TG1) includes tables 1, 2 and 3. Group 1 (TG1) includes tables 4, 5 and six. I ...
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1answer
68 views

Is it faster to split a large table into 12 rolling monthly tables & use UNION them for reports or keep large table & delete rows older than 1 year?

My co-worker wants to split a large 158M row stats table into stats_jan, stats_feb, ... and use UNION to select from them for reports. Is that standard practice and is it faster than to just use the ...
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2answers
241 views

How to sort rows after union

I have two tables that I want to combine. I need to be able to show all DelDates that had changes from the original (record 1). Record 1 as the first Record and Record 0 (table 2) always being the ...
1
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1answer
7k views

Msg 8114, Level 16, State 5, Line 1 Error converting data type nvarchar to float

I created some select statements which run without any problem in SQL Server. Then I joined them together with UNION and got this error message> Msg 8114, Level 16, State 5, Line 1 Error ...
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0answers
113 views

Does MySQL Lazy Union really work?

Following query is an example of Lazy Union: SELECT GREATEST(@found := -1, userId) AS userId FROM user WHERE userId = 1 UNION ALL SELECT userId FROM user WHERE userNumber = 1 AND @found IS NULL UNION ...
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1answer
4k views

syntax error at or near “AS” [closed]

I have a program that takes in one or more than one table names, from a list stored in a reference table and runs a SELECT query on it. so I retrieve the table names and insert it into the SELECT ...
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2answers
36 views

Optimizing PostgreSQL where clause with OR

I have a query that uses an or in the where clause. It is slow. It seems that re-writing the query using a union could get the same results much quicker. But I'm in an environment where we generate ...
1
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1answer
121 views

Get the combined row count by month from 3 tables

Using Postgres 10+, I have three tables with similar structures, where I'm trying to get a count of rows grouped by months. I have a functional query working for two tables, as below: CREATE TABLE ...
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1answer
831 views

Will too many tables slow Mysql down?

I'm making a database which should be able to handle over 1,000,000,000 rows. in order to optimize it's performance i've decided to split tables. so instead of having 1,000,000,000 entries in one ...
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1answer
62 views

Print Two Different Columns with Union All- SQL

I have an SQL statement like this, SELECT * FROM (select "John" as FirstName Union All select "Mary" Union All select "Alis"), (select "Doe" as LastName union all select "Queen" union all ...
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Combine multiple queries that each require a row of input values

I'm looking for a way to combine multiple queries that each need two values. For example, I can look up a patient's age and weight as follows: select age , weight from patients join ...
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1answer
378 views

Oracle DB union two select statements which return multiple rows

I am trying to create a union inside a stored procedure which unions two select statements. One of the select statement returns two or more rows. Thus I get the error "exact fetch returns more ...
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1answer
48 views

Handle 4 tables and to show 4 columns as result

i can't figure out how to build the correct query that involves 4 tables and shows these 4 columns: I want to show this 4 rows, each from a different table. EDIT: Each company belongs to a Sector. ...
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2answers
118 views

MySQL Select Union; Filter by Shared Relation?

Currently, I have 3 tables (see structure below), speakers, venues, and events. I'm trying to do a relevance search on the names of the speakers and venues. However, on the Search Results page, if the ...
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2answers
42 views

MYSQL search for each name in 2 columns and add values associated for each player

I have a database "game_results". It contains the following: PlayerID (int not null primary key auto increment) player1 (varchar) p1destroyed (int) player2 (varchar) p2destroyed (int) winner (...
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1answer
643 views

Backend Table/Row Locking Structure using CTE Queries

This question is an extension of a previous question that I asked. Table Locking When using Unions With the same query we are using that is causing blocking the various queries used in these UNIONS ...
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1answer
565 views

Table Locking When using Unions

When multiple selects are used in a UNION/UNION ALL are the table locks for each individual SELECT statement handled individually or are all table locks held until all SELECT statements are completed? ...
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2answers
62 views

Remove multiple joins to same table with where

I am stucked at below situation. Need expert advice. I have 3 tables, login_details,deleted_login_details and custom_fields as below. login_details structure = deleted_login_details custom-fields have ...
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1answer
228 views

Oracle Subselect Union Multiple Column

I want to select and count all cats and dogs at one location; location | cats | dogs | new york | 150 | 66 | paris | 34 | 12 | What I've got so far: SELECT cats,dogs FROM (select ...
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1answer
34 views

MySQL, comparison between, tables with not all records common, on 2 time intervals

I want to make comparisons on the volume of sales, turnover and margin of all product sales between 2 time intervals (2017-10-1 to 2017-10-31 ) and (2018-10-1 to 2018-10-31). for example: Product ...

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