SQL NULL Functions
SQL NULL Functions
SQL NULL functions are used to handle NULL values in SQL queries. NULL is a special value that represents the absence of a value or the unknown value, and can cause problems when performing calculations or comparisons in SQL. The following are some of the most common NULL functions in SQL:
- IS NULL: This function is used to check if a value is NULL or not. The syntax is as follows:
SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NULL;
In this syntax, the WHERE clause checks if the column_name has a NULL value or not.
- IS NOT NULL: This function is used to check if a value is not NULL. The syntax is as follows:
SELECT column1, column2, ...
FROM table_name
WHERE column_name IS NOT NULL;
In this syntax, the WHERE clause checks if the column_name has a non-NULL value.
- COALESCE: This function returns the first non-NULL value in a list of expressions. The syntax is as follows:
SELECT COALESCE(expression1, expression2, ...)
FROM table_name;
In this syntax, the COALESCE function checks each expression in order, and returns the first non-NULL value. If all expressions are NULL, then the COALESCE function returns NULL.
- NULLIF: This function compares two expressions and returns NULL if they are equal, otherwise it returns the first expression. The syntax is as follows:
SELECT NULLIF(expression1, expression2)
FROM table_name;
In this syntax, the NULLIF function compares expression1 and expression2. If they are equal, then the function returns NULL. If they are not equal, then the function returns expression1.
- NVL and IFNULL: These functions are used to replace NULL values with a specified value. The syntax for NVL is as follows:
SELECT NVL(column_name, replacement_value)
FROM table_name;
In this syntax, if the column_name is NULL, then the NVL function returns the replacement_value. If the column_name is not NULL, then the function returns the column_name. The IFNULL function works in a similar way in MySQL.
Overall, these NULL functions are useful tools for handling NULL values in SQL queries, and can help to prevent errors and unexpected results.