SQL Queries

SQL Queries

SQL queries are commands used to retrieve and manipulate data stored in a relational database. These queries allow you to perform various operations such as retrieving specific data, filtering data based on conditions, grouping data, and sorting data. Here are some commonly used SQL query clauses:

SELECT Query

The SELECT query is used to retrieve data from a database table. It allows you to specify the columns you want to retrieve and the table from which you want to retrieve the data.

Example:

sql
SELECT column1, column2
FROM table_name;

Explanation: This query retrieves column1 and column2 from the table_name table.

WHERE Clause

The WHERE clause is used to filter data based on specified conditions. It allows you to specify a condition that determines which rows should be included in the result set.

Example:

sql
SELECT column1, column2
FROM table_name
WHERE condition;

Explanation: This query retrieves column1 and column2 from the table_name table where the specified condition is met.

GROUP BY Clause

The GROUP BY clause is used to group rows based on one or more columns. It is often used in conjunction with aggregate functions to perform calculations on grouped data.

Example:

sql
SELECT column1, aggregate_function(column2)
FROM table_name
GROUP BY column1;

Explanation: This query groups the rows based on column1 and applies an aggregate function to column2 within each group.

HAVING Clause

The HAVING clause is used to filter the result set based on conditions applied to aggregated data. It allows you to specify a condition that applies to the result of an aggregate function.

Example:

sql
SELECT column1, aggregate_function(column2)
FROM table_name
GROUP BY column1
HAVING condition;

Explanation: This query groups the rows based on column1, applies an aggregate function to column2, and filters the result set based on the specified condition.

ORDER BY Clause

The ORDER BY clause is used to sort the result set based on one or more columns. It allows you to specify the sorting order as ascending (ASC) or descending (DESC).

Example:

sql
SELECT column1, column2
FROM table_name
ORDER BY column1 ASC, column2 DESC;

Explanation: This query retrieves column1 and column2 from the table_name table and sorts the result set in ascending order based on column1 and descending order based on column2.

These are some of the essential SQL query clauses that enable you to retrieve, filter, group, and sort data in a relational database.