A subquery can have only one column in the SELECT clause, unless multiple columns are in the main query for the subquery to compare its selected columns. You may use the IN, ANY, or ALL operator in outer query to handle a subquery that returns multiple rows. Subqueries are enclosed in parenthesis, this makes them easier to spot. Use the IN keyword for this subquery because you need to find values from more than one department. C. Main query and subquery must get data from the same tables D. Subqueries can contain ORDER BY but not the GROUP BY clause E. Only one column or expression can be compared between the main query and subqeury F. Multiple columns or expressions can be compared between the main query and subquery Answer: A, B, F Figure 3. Example #1. An ORDER BY command cannot be used in a subquery, although the main query can use an ORDER BY. How does a subquery use the main query columns? A subquery can be used anywhere an expression is allowed. 0. The query that contains the subquery is called an outer query or an outer select. A subquery, sometimes called a sub-SELECT, is a query whose results are used by another query. 0. When working with subqueries, the main statement is sometimes called the outer query. Multiple row subquery returns one or more rows to the outer SQL statement. Code: SELECT departmentname The main query uses the subquery’s result set as a comparison value for a selection criterion. Find the name of departments where the head of the department is from “Manhattan”. In Oracle database, a valid column name must begin with a letter, be less than or equal to 30 characters, and consist of only alphanumeric characters and the special characters $, _, and #. The GROUP BY command can be used to perform the same function as the ORDER BY in a subquery. Here is an example to understand subqueries in the WHERE clause. The subquery finds the managers who earn more than $20,000 a year, and the main query selects the salespeople who work for those managers. A subquery in the WHERE clause helps in filtering the rows for the result set, by comparing a column in the main table with the results of the subquery. Be careful when using subqueries. In this article. You create a subquery when you need to compare a field value to the results of a second query. Subquery : Subquery is query within query.The output of outer query is assigned to the column which is used in where condition of outer query.The subquery output is returning only one output value and based on that output value the outer query is executed.Subqueries are used in various real life scenarios like report development,Application logic development,Performance tuning of query. If it contains other characters, then it must be enclosed in double quotation marks. 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