What is the Difference Between Unique and Distinct in SQL

The main difference between Unique and Distinct in SQL is that Unique helps to ensure that all the values in a column are different while Distinct helps to remove all the duplicate records when retrieving the records from a table.

1. Does distinct mean unique?
2. How can I get unique records without distinct in SQL?
3. What is unique SQL?
4. Why distinct is bad in SQL?
5. How do you get distinct?
6. Why we use distinct in SQL query?
7. Does distinct slow down a query?
8. How do I get distinct rows in SQL?
9. What we can use instead of distinct in SQL?
10. Can foreign key be null?
11. How do I get a unique key in SQL?
12. How many nulls are allowed in unique key?

Does distinct mean unique?

The main difference between unique and distinct is that UNIQUE is a constraint that is used on the input of data and ensures data integrity. While DISTINCT keyword is used when we want to query our results or in other words, output the data.

How can I get unique records without distinct in SQL?

Below are alternate solutions :

1. Remove Duplicates Using Row_Number. WITH CTE (Col1, Col2, Col3, DuplicateCount) AS ( SELECT Col1, Col2, Col3, ROW_NUMBER() OVER(PARTITION BY Col1, Col2, Col3 ORDER BY Col1) AS DuplicateCount FROM MyTable ) SELECT * from CTE Where DuplicateCount = 1.
2. Remove Duplicates using group By.

What is unique SQL?

The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint.

Why distinct is bad in SQL?

Placing the DISTINCT inside a sub-query results in a somewhat bloated query for others to try and understand. Also, the DBMS might even perform worse from a performance perspective with the sub-query approach since it could cause indexes to be eliminated).

How do you get distinct?

How to use distinct in SQL?

1. SELECT DISTINCT returns only distinct (different) values.
2. DISTINCT eliminates duplicate records from the table.
3. DISTINCT can be used with aggregates: COUNT, AVG, MAX, etc.
4. DISTINCT operates on a single column.
5. Multiple columns are not supported for DISTINCT.

Why we use distinct in SQL query?

The SQL DISTINCT keyword is used in conjunction with the SELECT statement to eliminate all the duplicate records and fetching only unique records. There may be a situation when you have multiple duplicate records in a table.

Does distinct slow down a query?

Running with the DISTINCT keyword

If you do, your phone will ring, your pager will go vibrate, your users will have a hard time forgiving you, and performance will slow to a crawl for a little while. A quick examination of the query plan reveals that a table scan is still being used to retrieve the data from the table.

How do I get distinct rows in SQL?

The SQL SELECT DISTINCT Statement

The SELECT DISTINCT statement is used to return only distinct (different) values. Inside a table, a column often contains many duplicate values; and sometimes you only want to list the different (distinct) values.

What we can use instead of distinct in SQL?

Using GROUP BY instead of DISTINCT | SQL Studies.

Can foreign key be null?

Short answer: Yes, it can be NULL or duplicate. I want to explain why a foreign key might need to be null or might need to be unique or not unique. First remember a Foreign key simply requires that the value in that field must exist first in a different table (the parent table). ... Null by definition is not a value.

How do I get a unique key in SQL?

A unique key is a set of one or more than one fields/columns of a table that uniquely identify a record in a database table. You can say that it is little like primary key but it can accept only one null value and it cannot have duplicate values.

How many nulls are allowed in unique key?

The primary key column cannot have null values while the Unique Key column can have one null value.