if else in postgresql with code examples

The IF-ELSE statement in PostgreSQL is used to control the flow of a program based on a specific condition. The basic syntax of an IF-ELSE statement in PostgreSQL is as follows:

IF condition THEN
    statement1;
ELSE
    statement2;
END IF;

In this syntax, the condition is any valid expression that evaluates to a boolean value (TRUE or FALSE). If the condition is TRUE, the statement following the THEN keyword will be executed, and if the condition is FALSE, the statement following the ELSE keyword will be executed.

Here is an example of how you can use the IF-ELSE statement in PostgreSQL to check if a table exists and create it if it does not:

IF NOT EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'my_table') THEN
    CREATE TABLE my_table (id INT, name VARCHAR(50));
ELSE
    RAISE NOTICE 'Table already exists.';
END IF;

In this example, the IF statement checks if a table named my_table exists in the information_schema.tables view. If the table does not exist, the CREATE TABLE statement will be executed to create the table. If the table already exists, a notice will be raised to inform the user that the table already exists.

You can also use the IF-ELSE statement in the context of a stored procedure or function. Here is an example of how you can use the IF-ELSE statement in a stored function to check if a value passed as an argument is greater than or equal to a specific value:

CREATE OR REPLACE FUNCTION check_value(value INT)
RETURNS BOOLEAN AS $$
BEGIN
    IF value >= 10 THEN
        RETURN TRUE;
    ELSE
        RETURN FALSE;
    END IF;
END;
$$ LANGUAGE plpgsql;

In this example, the function check_value takes an integer value as an argument and returns a boolean value indicating whether the value is greater than or equal to 10.

The IF-ELSE statement in PostgreSQL provides a powerful way to control the flow of a program based on specific conditions. With the examples above, you should have a good understanding of how to use the IF-ELSE statement in PostgreSQL and be able to implement it in your own database projects.

In addition to the IF-ELSE statement, PostgreSQL also provides the CASE statement which can be used to evaluate multiple conditions. The CASE statement has the following basic syntax:

CASE value
WHEN compare_value1 THEN result1
WHEN compare_value2 THEN result2
...
ELSE result_else
END CASE;

In this syntax, the value is the expression that you want to evaluate. The compare_value1, compare_value2, etc. are the values that you want to compare the value to. The result1, result2, etc. are the expressions that will be returned if the value matches the corresponding compare_value. The result_else is the expression that will be returned if none of the compare_value matches the value.

Here is an example of how you can use the CASE statement in PostgreSQL to assign a letter grade to a numerical score:

SELECT name, score,
CASE
    WHEN score >= 90 THEN 'A'
    WHEN score >= 80 THEN 'B'
    WHEN score >= 70 THEN 'C'
    WHEN score >= 60 THEN 'D'
    ELSE 'F'
END as "Grade"
FROM student;

In this example, the CASE statement is used to assign a letter grade to the score column of the student table. If the score is greater than or equal to 90, the grade will be 'A', if the score is greater than or equal to 80, the grade will be 'B', etc.

Another control flow statement provided by PostgreSQL is the LOOP statement, which allows you to execute a block of statements repeatedly. The LOOP statement has the following basic syntax:

<<label>>
LOOP
    statements;
    EXIT label WHEN condition;
END LOOP label;

In this syntax, the label is an optional label that can be used to identify the loop. The statements are the statements that will be executed repeatedly. The EXIT statement is used to exit the loop when the specified condition is met.

Here is an example of how you can use the LOOP statement in PostgreSQL to print the numbers from 1 to 10:

DO $$
DECLARE
    i INT := 1;
BEGIN
    LOOP
        RAISE NOTICE 'Current number: %', i;
        i := i + 1;
        EXIT WHEN i > 10;
    END LOOP;
END $$;

In this example, the LOOP statement is used to execute the RAISE NOTICE statement repeatedly. The EXIT statement is used to exit the loop when the value of the variable i becomes greater than 10.

PostgreSQL also provides the WHILE loop, which allows you to execute a block of statements repeatedly until a specified condition is met. The WHILE loop has the following basic syntax:

WHILE condition LOOP
    statements;
END LOOP;

In this syntax, the condition is the condition that will be evaluated before each iteration of the loop. The statements are the statements that will be executed repeatedly as long as the condition is TRUE.

In summary,

Popular questions

What is the basic syntax of an IF-ELSE statement in PostgreSQL?

The basic syntax of an IF-ELSE statement in PostgreSQL is as follows:

IF condition THEN
    statement1;
ELSE
    statement2;
END IF;

How can you use the IF-ELSE statement in PostgreSQL to check if a table exists and create it if it does not?

You can use the IF-ELSE statement in PostgreSQL to check if a table exists and create it if it does not as follows:

IF NOT EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'my_table') THEN
    CREATE TABLE my_table (id INT, name VARCHAR(50));
ELSE
    RAISE NOTICE 'Table already exists.';
END IF;

Can you use the IF-ELSE statement in the context of a stored procedure or function in PostgreSQL?

Yes, you can use the IF-ELSE statement in the context of a stored procedure or function in PostgreSQL. Here is an example of how you can use the IF-ELSE statement in a stored function to check if a value passed as an argument is greater than or equal to a specific value:

CREATE OR REPLACE FUNCTION check_value(value INT)
RETURNS BOOLEAN AS $$
BEGIN
    IF value >= 10 THEN
        RETURN TRUE;
    ELSE
        RETURN FALSE;
    END IF;
END;
$$ LANGUAGE plpgsql;

In this example, the function check_value takes an integer value as an argument and returns a boolean value indicating whether the value is greater than or equal to 10.

How can you use the CASE statement in PostgreSQL to assign a letter grade to a numerical score?

You can use the CASE statement in PostgreSQL to assign a letter grade to a numerical score as follows:

SELECT name, score,
CASE
    WHEN score >= 90 THEN 'A'
    WHEN score >= 80 THEN 'B'
    WHEN score >= 70 THEN 'C'
    WHEN score >= 60 THEN 'D'
    ELSE 'F'
END as "Grade"
FROM student;

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Control-Flow.

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