SQL SELECT NULL
When working with databases, handling NULL values is essential. Before writing queries, it helps to understand what NULL means in SQL.
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What is NULL in SQL?
NULL represents missing or unknown data. A column holds NULL when no value is provided during insertion or update.
Note: NULL is NOT the same as 0 or an empty string (""). It means the absence of any value.
1. WHERE IS NULL
To find records where a column has NULL values, use IS NULL:
SELECT SIR_NAME, NAME, MARKS
FROM STUDENTS
WHERE MARKS IS NULL;2. WHERE IS NOT NULL
To find records that have actual data (not NULL), use IS NOT NULL:
SELECT SIR_NAME, NAME, MARKS
FROM STUDENTS
WHERE MARKS IS NOT NULL;Handling NULL with COALESCE and IFNULL
You can replace NULL values with a default using COALESCE (standard SQL) or IFNULL (MySQL):
SELECT NAME, COALESCE(MARKS, 0) AS Marks
FROM STUDENTS;
-- MySQL alternative
SELECT NAME, IFNULL(MARKS, 0) AS Marks FROM STUDENTS;NULL in Aggregate Functions
Important: aggregate functions like AVG(), SUM(), and COUNT(column) ignore NULL values. However, COUNT(*) counts all rows including those with NULLs.
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Conclusion
Handling NULL properly is crucial in SQL. Use IS NULL and IS NOT NULL to filter, and COALESCE/IFNULL to substitute defaults. Remember that aggregates ignore NULLs. For more professional SQL tutorials, stay tuned to .
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