What does Union do in SQL Server?

What is the function of union in SQL?

The Union operator combines the results of two or more queries into a distinct single result set that includes all the rows that belong to all queries in the Union. In this operation, it combines two more queries and removes the duplicates. For example, the table ‘A’ has 1,2, and 3 and the table ‘B’ has 3,4,5.

What is difference between union and union all in SQL Server?

UNION ALL command is equal to UNION command, except that UNION ALL selects all the values. The difference between Union and Union all is that Union all will not eliminate duplicate rows, instead it just pulls all the rows from all the tables fitting your query specifics and combines them into a table.

Does Union in SQL remove duplicates?

The SQL UNION ALL operator is used to combine the result sets of 2 or more SELECT statements. It does not remove duplicate rows between the various SELECT statements (all rows are returned). Each SELECT statement within the UNION ALL must have the same number of fields in the result sets with similar data types.

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What is query for second highest salary?

We can nest the above query to find the second largest salary. select *from employee group by salary order by salary desc limit 1,1; There are other ways : SELECT name, MAX(salary) AS salary FROM employee WHERE salary IN (SELECT salary FROM employee MINUS SELECT MAX(salary) FROM employee);

Which is faster union or union all?

UNION ALL is faster and more optimized than UNION. But we cannot use it in all scenarios. UNION ALL with SELECT DISTINCT is not equivalent to UNION.

What can be used instead of union in SQL?

There are several alternatives to the union SQL operator:

  • Use UNION ALL.
  • Execute each SQL separately and merge and sort the result sets within your program! …
  • Join the tables. …
  • In versions, 10g and beyond, explore the MODEL clause.
  • Use a scalar subquery.

Is full join same as union?

They’re completely different things. A join allows you to relate similar data in different tables. A union returns the results of two different queries as a single recordset. Joins and unions can be used to combine data from one or more tables.

What is the biggest difference between union and union all?

The only difference between Union and Union All is that Union extracts the rows that are being specified in the query while Union All extracts all the rows including the duplicates (repeated values) from both the queries.

How do you find the third highest salary?

To Find the Third Highest Salary Using a Sub-Query,

  1. SELECT TOP 1 SALARY.
  2. FROM (
  3. SELECT DISTINCT TOP 3 SALARY.
  4. FROM tbl_Employees.
  5. ORDER BY SALARY DESC.
  6. ) RESULT.
  7. ORDER BY SALARY.
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Does Union all sort?

No it does not. SQL tables are inherently unordered. You need to use order by to get things in a desired order.

Categories SQL