Distinct

The DISTINCT keyword is used to remove duplicate values from a result of a SQL or SPARQL query.

Union

Use this tag only for questions about UNION, a keyword of the SQL language for combining the results of multiple SQL queries

Note rows outer

Quality Example
Faster

"A side note since you want all rows using union all is faster since it does not need to perform a distinct to eliminate duplicates"

from question "SQL select from table and get table name"

"I am currently using union all and a distinct in the outer query as this proved much faster than using union s for the uniqueness of data"

from question "Should I use a T-SQL function, view, or stored proc?"

Slower de-dupping tables

Quality Example
Slower

"Union distinct is slower than union all but you may need it for de-dupping."

from question "How to optimize select sum() on mysql?"

"Keep in mind that union will return a distinct list - duplicates will be removed but it will perform slower than using union all which will not remove duplicates"

from question "Checking if a string is found in one of multiple columns in mySQL"

Faster

"However the tables are huge and the union all i read its faster than distinct takes forever to execute even with just two tables let alone 6"

from question "MySQL: Optimizing SELECT from 6 huge identical tables with different data split up by timestamp"

"Union all is generally faster than using distinct or grouping"

from question "SQL Server : shortest syntax using distinct?"

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