How to identify columns with all NULL values in a table (Basic 1 - 3)

There are different ways to identify columns with all NULL values in a table. One simple way is to use the following SQL code:

SQL

SELECT column_name
FROM information_schema.columns
WHERE table_name = 'table_name'
AND data_type NOT IN ('BLOB', 'CLOB', 'NCLOB')
AND is_nullable = 'YES'
AND column_name NOT IN (
    SELECT column_name
    FROM information_schema.statistics
    WHERE table_name = 'table_name'
    AND num_distinct = 1
);

This code will return a list of all columns in the table_name table that are null and do not contain any distinct values.

Another way to identify columns with all NULL values in a table is to use the following query:

SQL

SELECT column_name
FROM information_schema.columns
WHERE table_name = 'table_name'
AND data_type NOT IN ('BLOB', 'CLOB', 'NCLOB')
AND is_nullable = 'YES'
AND column_name NOT IN (
    SELECT column_name
    FROM (
        SELECT column_name, COUNT(*) AS num_distinct
        FROM 'table_name'
        GROUP BY column_name
    ) AS t
    WHERE num_distinct > 0
);

This query is similar to the previous one, but it also excludes columns that contain at least one non-NULL value.

Once you have identified columns with all NULL values in a table, you can decide to remove them or keep them, depending on your needs. If you decide to remove them, you can use the following SQL statement:

SQL

ALTER TABLE table_name DROP COLUMN column_name;

Note: Before removing any column from a table, it is important to back up the table.

I have made the following changes to the text:

• I have changed the title to be more concise and informative.
• I have added a brief introduction to the topic.
• I have explained the two different ways to identify columns with all NULL values in a table.
• I have added a note about the importance of backing up a table before removing any columns.

I hope this is helpful. Please let me know if you have any questions.