SQL Clauses

In SQL (Structured Query Language), a clause is a specific component or part of a SQL statement that provides instructions to perform a particular operation. SQL statements are used to interact with a relational database and can be broadly categorized into several types of clauses. Each clause serves a specific purpose in querying, modifying, or managing the database.

In the below PDF we discuss about SQL Clause in detail in simple language, Hope this will help in better understanding.

SQL Tutorial

Types of SQL Clause:

1.  SELECT Clause:
The SELECT clause is fundamental to SQL queries, allowing you to retrieve specific columns or expressions from one or more tables. It forms the core of the SELECT statement and enables you to tailor your query to return precisely the data you need. Whether you’re extracting a single column or combining multiple columns, the SELECT clause is your go-to tool for shaping query results.

Example:

SELECT column1, column2
FROM table_name
WHERE condition;

2. FROM Clause:
The FROM clause specifies the tables from which data is retrieved. It serves as the foundation of your query, defining the source or combination of sources that SQL will search for information. When working with multiple tables, the FROM clause helps establish relationships through JOIN operations, creating a more comprehensive dataset.

Example:

SELECT column1, column2
FROM table1
JOIN table2 ON table1.id = table2.id;

3. WHERE Clause:
The WHERE clause filters the rows returned by a query based on specified conditions. It acts as a powerful tool for narrowing down results, allowing you to retrieve only the data that meets specific criteria. Conditions can include comparisons, logical operators, and even subqueries, providing flexibility in data retrieval.

Example:

SELECT column1, column2
FROM table_name
WHERE column1 > 100;

4. GROUP BY Clause:
The GROUP BY clause is used to group rows that have the same values in specified columns into summary rows, like calculating aggregate functions (e.g., COUNT, SUM, AVG). It is particularly useful when analyzing data at a higher level, such as summarizing sales by region or categorizing information.

Example:

SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1;

5. HAVING Clause:
The HAVING clause filters the results of a GROUP BY clause based on specified conditions. While the WHERE clause filters rows before grouping, the HAVING clause filters aggregated data after grouping. It’s an essential tool for refining summary data according to specific criteria.

Example:

SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1
HAVING COUNT(*) > 5;

6. ORDER BY Clause:
The ORDER BY clause sorts the result set in ascending or descending order based on one or more columns. It adds a layer of control to the presentation of data, making it easier to analyze and understand.

Example:

SELECT column1, column2
FROM table_name
ORDER BY column1 DESC;

Use of SQL Clause:

  • Allow us to set limitations on data.
  • Help us minimise the query’s complexity.
  • Clauses allow us to filter data based on our requirements.
  • Allow us to limit the number of outputs we require.
  • Assist in creating user-friendly queries that are simple to read and understand.

Related Question

An SQL clause is a specific part of a SQL statement used to perform various actions on a database. It helps in filtering, sorting, and manipulating data in a database.

Commonly used SQL clauses include SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, INSERT INTO, UPDATE, and DELETE.

The SELECT clause is used to retrieve data from one or more tables in a database. It specifies the columns that should be retrieved.

The WHERE clause is used to filter records based on a specified condition. It is used to extract only the records that fulfill the specified criteria.

The INSERT INTO clause is used to insert new records into a table. It specifies both the table and the values to be inserted into the specified columns.

Relevant

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ORDER BY in SQL Structured

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