{"id":168,"date":"2024-08-21T06:09:39","date_gmt":"2024-08-21T06:09:39","guid":{"rendered":"https:\/\/techkubo.com\/sql\/?p=168"},"modified":"2025-05-09T08:56:57","modified_gmt":"2025-05-09T08:56:57","slug":"sql-null-values","status":"publish","type":"post","link":"https:\/\/techkubo.com\/sql\/sql-null-values\/","title":{"rendered":"SQL Null Values"},"content":{"rendered":"\n

In SQL, ‘Null’ represents the absence of a value or an unknown value. It is used to signify that a data field does not contain any data or that the value is missing. Having a ZERO value and NO value is not the same.<\/p>\n\n\n\n


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SQL Null Values Syntax<\/h2>\n\n\n\n

SQL Null Values Inserting NULL Values Syntax<\/h3>\n\n\n\n
INSERT INTO table_name (column1, column2, ...)\nVALUES (value1, NULL, ...);<\/pre><\/div>\n\n\n\n

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SQL Null Values Updating to NULL Syntax<\/h3>\n\n\n\n
UPDATE table_name\nSET column_name = NULL\nWHERE condition;<\/pre><\/div>\n\n\n\n

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SQL Null Values Selecting Non-NULL Values<\/h3>\n\n\n\n
SELECT column1, column2, ...\nFROM table_name\nWHERE column_name IS NOT NULL;<\/pre><\/div>\n\n\n\n

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SQL Null Values Example<\/h2>\n\n\n\n
SQL Null Values Inserting NULL Values Example<\/h3>\n\n\n\n
This query effectively adds a record for a patient named Alice Brown, born on April 23,1991, with the gender indicated as female. The patient’s contact number is not included, which is acceptable due to the contact_number column allowing NULL values.<\/p>\n\n\n\n
INSERT INTO Patients (patient_id, first_name, last_name, dob, gender, contact_number)\nVALUES (13, 'Alice', 'Brown', '1991-04-23', 'F', NULL);<\/pre><\/div>\n\n\n\n
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Try It Out!<\/a><\/div>\n<\/div>\n\n\n\n

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SQL Null Values Updating a Column to NULL<\/h3>\n\n\n\n
This query effectively updates  the record for the patient with patient_id 12 by setting the contact_number to NULL. This means the contact number for this specific patient is now absent or undefined, and this update is applied only to the record with patient_id = 12.<\/p>\n\n\n\n
UPDATE Patients\nSET contact_number = NULL\nWHERE patient_id = 12;<\/pre><\/div>\n\n\n\n
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SQL Null Values Selecting Records with NULL Values Example<\/h3>\n\n\n\n
This query retrieves the first_name and last_name of all patients from the Patients table where the contact_number is set to NULL. This means it will return the names of patients who do not have a recorded contact number.<\/p>\n\n\n\n
SELECT first_name, last_name\nFROM Patients\nWHERE contact_number IS NULL;<\/pre><\/div>\n\n\n\n
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SQL Null Values Selecting Records with Non-NULL Values Example<\/h3>\n\n\n\n
This query retrieves the first_name, last_name, and contact number of all patients from the Patients table where the contact_number is not NULL.<\/p>\n\n\n\n
SELECT first_name, last_name, contact_number\nFROM Patients\nWHERE contact_number IS NOT NULL;<\/pre><\/div>\n\n\n\n
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SQL Null Values Visual Diagram<\/h2>\n\n\n\n
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SQL Null Values Labs<\/h2>\n\n\n\n