![]() ![]() WHEN author_exp >= 0 AND author_exp 1 AND author_exp 3 AND author_exp 5 THEN 'Expert' In the following statement, we will use the CASE expression to check if the author is a “freshman” “junior”, “senior”, or “expert”: SELECT author_name, author_exp, In this example, we will apply the CASE statement on the “author_info” table, whose data is shown in the following snippet: SELECT * For instance, if “condition_1” satisfies the “search_expression” then “result_1” will be retrieved.Įxample 1: How Does the Searched CASE Statement Work in Postgres? When a condition retrieves a “TRUE” value then the result associated with that condition will be retrieved. The “Search_expression” represents an expression to be evaluated against the expression specified in each “WHEN” case. The below snippet illustrates the syntax of a simple CASE statement: CASE search_expression If all the conditions/expressions retrieve “FALSE” then the result associated with the “ELSE” block will be executed. This process will continue until an expression retrieves true. However, if a condition retrieves a “FALSE” value, then the CASE expression will evaluate the next condition. Once the CASE statement encounters that an expression retrieves a TRUE value, then immediately, it will stop evaluating the remaining expressions. For instance, when “condition_1” becomes true, then “result_1” will be retrieved. ![]() The CASE statement will execute each condition specified within the CASE statement from top-to-bottom. The conditions, such as codition_1, condition_2, …, condition_n, are the boolean conditions that will retrieve either true or false. Let’s comprehend the above syntax line-by-line: The below snippet depicts the syntax of a searched CASE statement: CASE Postgres supports two forms of the CASE statement: A Searched CASE and a Simple CASE. What is CASE Statement and How to Write it in Postgres?Īs stated earlier, the CASE statement is a conditional expression, so it can be used with any statement or clause where an expression can be used, such as a WHERE clause, SELECT statement, etc. This post illustrates several use cases of the CASE statement in PostgreSQL via practical examples. with the CASE statement to create or formulate a query/expression. PostgreSQL allows us to use the WHEN-THEN case, if-else statements, etc. The CASE statement is one of the conditional expressions that is used to create conditional queries. These statements include if, if-else, case, etc. See SQL CASE Statement for examples.Conditional statements are the core concepts in any programming paradigm. We can use it pretty much anywhere a valid expression can be used.įor example, we can use the CASE operator as part of an UPDATE statement when updating data in a database. The CASE operator isn’t limited to just SELECT statements. Using the CASE Operator in Other Contexts That’s because I set up psql to return that string for NULL values. In my case, NULL values are represented by the string. Let’s omit the ELSE clause from the first example: SELECT If we omit the ELSE clause, and none of the conditions are met, the result is NULL. ![]() The above examples use the ELSE clause to determine what happens if none of the conditions are met, however, the ELSE clause is optional. We could rewrite this to a searched CASE expression if we wanted. Here’s an example to demonstrate the simple CASE expression: SELECT The searched CASE expression evaluates a set of Boolean expressions to determine the result. The other option is the searched CASE expression: CASE The simple CASE expression compares an expression to a set of simple expressions to determine the result. One form is the simple CASE expression: CASE value The basic syntax for the CASE expression goes like this: CASE WHEN condition THEN resultĪctually, there are two forms of CASE expression. The CASE expression is included in the SQL standard (ISO/IEC 9075), and most major RDBMSs support it. In PostgreSQL, the CASE expression compares a list of conditions and returns one of multiple possible result expressions. ![]()
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