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WHERE Clause - (PostgreSQL)

The WHERE clause in PostgreSQL is used to filter the result set of a query based on a specified condition. It allows you to retrieve only the records that match a certain criteria. In this tutorial, we'll discuss the syntax, example, output, explanation, use, important points, and summary of the WHERE clause in PostgreSQL.

Syntax

The basic syntax of the WHERE clause in PostgreSQL is as follows:

SELECT column1, column2, ...
FROM table_name
WHERE condition;

Example

Let's take a look at an example of using the WHERE clause in a PostgreSQL query:

SELECT *
FROM students
WHERE age > 18;

This query selects all columns from the students table where the age column is greater than 18.

Output

The output of the above query will be a list of all records in the students table where the age column is greater than 18.

Explanation

In this example, we used the WHERE clause to filter the result set based on a condition (age > 18). This condition is evaluated for each row in the students table, and only those rows where the condition is true are included in the final result set.

Use

The WHERE clause is used to filter the result set of a query based on a specified condition. It is commonly used in conjunction with other clauses like SELECT, FROM, GROUP BY, HAVING, and ORDER BY.

The WHERE clause can be used to filter the result set based on one or more conditions. Multiple conditions can be combined using logical operators like AND, OR, and NOT.

Important Points

  • The condition specified in the WHERE clause can be a simple comparison expression, a range expression, or a complex expression involving multiple operators and functions.
  • The WHERE clause is optional in a SQL query. If not specified, the result set will include all rows from the table(s).
  • The WHERE clause is evaluated for each row in the table, and only those rows for which the condition evaluates to true are included in the final result set.
  • The WHERE clause is case-insensitive in PostgreSQL.

Summary

In this tutorial, we discussed the WHERE clause in PostgreSQL. We covered the syntax, example, output, explanation, use, and important points of the WHERE clause. Now that you understand the basics of the WHERE clause, you can use it in your PostgreSQL queries to filter the result set based on specific conditions.

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