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NULL is used in SQL to indicate that a value doesn't exist in the database. It's not to be confused with an empty string or a zero value. While NULL indicates the absence of a value, the empty string and zero both represent actual values.
Since the phone number is a unique field, the user with no phone number will get added. However, it will throw an error of unique constraint if you use an empty string here. So, NULL is better. An empty string is useful when the data comes from multiple resources.
You need to use NULLIF() function from MySQL. The syntax is as follows: SELECT NULLIF(yourCoumnName,' ') as anyVariableName from yourTableName; In the above syntax, if you compare empty string( ' ') to empty string( ' '), the result will always be NULL.
There are two ways to replace NULL with blank values in SQL Server, function ISNULL(), and COALESCE(). Both functions replace the value you provide when the argument is NULL like ISNULL(column, '') will return empty String if the column value is NULL.
Select *
From Table
Where (col is null or col = '')
Or
Select *
From Table
Where IsNull(col, '') = ''
If you need it in SELECT section can use like this.
SELECT ct.ID,
ISNULL(NULLIF(ct.LaunchDate, ''), null) [LaunchDate]
FROM [dbo].[CustomerTable] ct
You can replace the null with your substitution value.
You can simply do this:
SELECT *
FROM yourTable
WHERE yourColumn IS NULL OR yourColumn = ''
SELECT *
FROM TableName
WHERE columnNAme IS NULL OR
LTRIM(RTRIM(columnName)) = ''
To find rows where col is NULL, empty string or whitespace (spaces, tabs):
SELECT *
FROM table
WHERE ISNULL(LTRIM(RTRIM(col)),'')=''
To find rows where col is NOT NULL, empty string or whitespace (spaces, tabs):
SELECT *
FROM table
WHERE ISNULL(LTRIM(RTRIM(col)),'')<>''
Some sargable methods...
SELECT *
FROM #T
WHERE SomeCol = '' OR SomeCol IS NULL;
SELECT *
FROM #T
WHERE SomeCol = ''
UNION ALL
SELECT *
FROM #T
WHERE SomeCol IS NULL;
SELECT *
FROM #T
WHERE EXISTS ((SELECT NULL UNION SELECT '') INTERSECT SELECT SomeCol);
And some non-sargable ones...
SELECT *
FROM #T
WHERE IIF(SomeCol <> '',0,1) = 1;
SELECT *
FROM #T
WHERE NULLIF(SomeCol,'') IS NULL;
SELECT *
FROM #T
WHERE ISNULL(SomeCol,'') = '';
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