What is subquery in SQL?

A subquery is a query that is nested inside a SELECT , INSERT , UPDATE , or DELETE statement, or inside another subquery.

What is subquery in SQL with example?

In SQL, it's possible to place a SQL query inside another query known as subquery. For example, SELECT * FROM Customers WHERE age = ( SELECT MIN(age) FROM Customers ); In a subquery, the outer query's result is dependent on the result-set of the inner subquery. That's why subqueries are also called nested queries.

Why subquery is used in SQL?

A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved. Subqueries can be used with the SELECT, INSERT, UPDATE, and DELETE statements along with the operators like =, <, >, >=, <=, IN, BETWEEN, etc.

What is subquery and its types in SQL?

Type of Subqueries

Single row subquery : Returns zero or one row. Multiple row subquery : Returns one or more rows. Multiple column subqueries : Returns one or more columns. Correlated subqueries : Reference one or more columns in the outer SQL statement.

What are the different types of a subquery?

Subquery In SQL | SQL Subquery Tutorial With Examples | SQL Tutorial For Beginners | Simplilearn

How many subqueries are there in SQL?

There are three broad types of a subquery in SQL. This chapter from OCA Oracle Database 11g: SQL Fundamentals I Exam Guide explains differences between a single-row subquery, multiple-row subquery and correlated subquery .

What is subquery and its properties?

A subquery is also known as a nested query which means query inside another query. A subquery is used to return data that will be used in the main query as a condition to further restrict the data to be retrieved. Properties of Sub-Query A subquery should be boxed within the parenthesis.

What is meant by subquery?

A subquery is a query that appears inside another query statement. Subqueries are also referred to as sub- SELECT s or nested SELECT s. The full SELECT syntax is valid in subqueries.

What is the difference between nested query and subquery?

A subquery, also known as a nested query or subselect, is a SELECT query embedded within the WHERE or HAVING clause of another SQL query. The data returned by the subquery is used by the outer statement in the same way a literal value would be used.

What is difference between subquery and correlated query?

With a normal nested subquery, the inner SELECT query runs first and executes once, returning values to be used by the main query. A correlated subquery, however, executes once for each candidate row considered by the outer query. In other words, the inner query is driven by the outer query.

What is difference between join and subquery?

A SQL Join statement is used to combine data or rows from two or more tables based on a common field between them. A subquery is a query that is nested inside a SELECT , INSERT , UPDATE , or DELETE statement, or inside another subquery.

What is subquery in MySQL?

In MySQL, a subquery is a query within a query. You can create subqueries within your SQL statements. These subqueries can reside in the WHERE clause, the FROM clause, or the SELECT clause.

What is SQL Indexing?

A SQL index is used to retrieve data from a database very fast. Indexing a table or view is, without a doubt, one of the best ways to improve the performance of queries and applications. A SQL index is a quick lookup table for finding records users need to search frequently.

How does a subquery work?

A subquery is a query within another query. The outer query is called as main query and inner query is called as subquery. The subquery generally executes first, and its output is used to complete the query condition for the main or outer query. Subquery must be enclosed in parentheses.

Is a subquery faster than a join?

Advantages Of Joins:

The retrieval time of the query using joins almost always will be faster than that of a subquery. By using joins, you can maximize the calculation burden on the database i.e., instead of multiple queries using one join query.

What is query in SQL?

A query is a request for data or information from a database table or combination of tables. This data may be generated as results returned by Structured Query Language (SQL) or as pictorials, graphs or complex results, e.g., trend analyses from data-mining tools.

How many types of JOINs in SQL?

JOINS are used to fetch data from database tables and represent the result dataset as a separate table. How many types of JOINs are there in SQL? There are four main types of JOINs in SQL: INNER JOIN, OUTER JOIN, CROSS JOIN, and SELF JOIN.

What is difference union and union all in SQL?

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.

What is a regular subquery?

The main difference between a regular, non-correlated, and correlated subquery in SQL is in their working, a regular subquery just runs once and returns a value or a set of values that is used by the outer query.

What is subquery in SQL Mcq?

d) A subquery is a condition that excludes all the invalid tuples from the database. Explanation: A subquery is a select-from-where expression that is nested within another query. Common uses for sub-queries are to perform tests for set membership, make set comparisons etc.

What is subquery SQL w3schools?

Subquery or Inner query or Nested query is a query in a query. SQL subquery is usually added in the WHERE Clause of the SQL statement. Most of the time, a subquery is used when you know how to search for a value using a SELECT statement, but do not know the exact value in the database.

What is single row subquery in SQL?

A single-row subquery is used when the outer query's results are based on a single, unknown value. Although this query type is formally called "single-row," the name implies that the query returns multiple columns-but only one row of results.

Which of the following is not an operator used in single row sub queries?

Answer: C. Multi-row operators cannot be used in single-row sub-queries and vice versa.

What is trigger in SQL?

A trigger is a special type of stored procedure that automatically runs when an event occurs in the database server. DML triggers run when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view.

How do you DELETE duplicates in SQL?