What is select distinct in SQL?

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 is the difference between SELECT and SELECT distinct?

What is the difference between select and select distinct. SELECT DISTINCT statement is used for returning only distinct (different) values from a column. SELECT statement is used for returning all the values in the table column.

How does SELECT distinct work?

When only one expression is provided in the DISTINCT clause, the query will return the unique values for that expression. When more than one expression is provided in the DISTINCT clause, the query will retrieve unique combinations for the expressions listed. In SQL, the DISTINCT clause doesn’t ignore NULL values.

What is distinct in SQL with examples?

SELECT DISTINCT returns only distinct (different) values. DISTINCT eliminates duplicate records from the table. DISTINCT can be used with aggregates: COUNT, AVG, MAX, etc. DISTINCT operates on a single column.

Example: DISTINCT Clause handles NULL Values

  • SELECT DISTINCT fruit_id.
  • FROM fruits.
  • ORDER BY category_id;
IT IS INTERESTING:  Your question: What is Java System time?

Does distinct include NULL?

The DISTINCT clause counts only those columns having distinct (unique) values. … COUNT DISTINCT does not count NULL as a distinct value.

How do you eliminate duplicate rows in SQL query without distinct?

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.

How do I select distinct values from multiple columns in SQL?

Select with distinct on all columns of the first query. Select with distinct on multiple columns and order by clause. Count() function and select with distinct on multiple columns.

What is difference between unique and distinct?

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 do I count distinct rows in SQL?

The COUNT DISTINCT function returns the number of unique values in the column or expression, as the following example shows. SELECT COUNT (DISTINCT item_num) FROM items; If the COUNT DISTINCT function encounters NULL values, it ignores them unless every value in the specified column is NULL.

Can we apply distinct on multiple columns?

Yes, the DISTINCT clause can be applied to any valid SELECT query. It is important to note that DISTINCT will filter out all rows that are not unique in terms of all selected columns.

IT IS INTERESTING:  Why do business analysts need SQL skills?

Can we use distinct and count together in SQL?

Yes, you can use COUNT() and DISTINCT together to display the count of only distinct rows. SELECT COUNT(DISTINCT yourColumnName) AS anyVariableName FROM yourTableName; … If you do not use DISTINCT, then COUNT() function gives the count of all rows.

What is distinct salary?

First, let us see how the following SELECT query returns the duplicate salary records. … Now, let us use the DISTINCT keyword with the above SELECT query and then see the result. SQL> SELECT DISTINCT SALARY FROM CUSTOMERS ORDER BY SALARY; This would produce the following result where we do not have any duplicate entry.

Why distinct is bad in SQL?

The fact that the resultset has duplicates is frequently (though not always) the result of a poor database design, an ineffective query, or both. In any case, issuing the query without the DISTINCT keyword yields more rows than expected or needed so the keyword is employed to limit what is returned to the user.

Does count (*) ignore NULL values?

Using SELECT COUNT(*) or SELECT COUNT(1) (which is what I prefer to use) will return the total of all records returned in the result set regardless of NULL values. … Since the COUNT (and other aggregate functions) will ignore NULL values we use the CASE to turn NULLs into values and values into NULLs.

How does distinct handle NULL values?

Using the SQL DISTINCT with NULL

The DISTINCT operator treats NULL duplicate. It means that the two NULLs are the same. Therefore, if the SELECT statement returns NULL s, the DISTINCT returns only one NULL . As you can see from the output, the query returns duplicate regions.

IT IS INTERESTING:  Is Java enough to get a job?

What will count (*) do?

The COUNT (*) function returns the number of rows that satisfy the WHERE clause of a SELECT statement.

Secrets of programming