MySQL select where column is not empty

Question

In MySQL, can I select columns only where something exists?

For example, I have the following query:

select phone, phone2
from jewishyellow.users
wh         


        

Answer 1

We can use CASE for setting blank value to some char or String. I am using NA as Default string.

SELECT phone,   
CASE WHEN phone2 = '' THEN 'NA' END AS phone2 ELSE ISNULL(phone2,0) 
FROM jewishyellow.users  WHERE phone LIKE '813%'

Answer 2

select phone, phone2 from jewishyellow.users 
where phone like '813%' and phone2 is not null

Answer 3

Compare value of phone2 with empty string:

select phone, phone2 
from jewishyellow.users 
where phone like '813%' and phone2<>''

Note that NULL value is interpreted as false.

Answer 4

Another alternative is to look specifically at the CHAR_LENGTH of the column values. (not to be confused with LENGTH)

Using a criteria where the character length is greater than 0, will avoid false positives when the column values can be falsey, such as in the event of an integer column with a value of 0 or NULL. Behaving more consistently across varying data-types.

Which results in any value that is at least 1 character long, or otherwise not empty.

Example https://www.db-fiddle.com/f/iQvEhY1SH6wfruAvnmWdj5/1

SELECT phone, phone2
FROM users
WHERE phone LIKE '813%'
AND CHAR_LENGTH(phone2) > 0

Table Data

users
phone (varchar 12) | phone2 (int 10)
"813-123-4567"     | NULL
"813-123-4567"     | 1
"813-123-4567"     | 0

users2
phone (varchar 12) | phone2 (varchar 12)
"813-123-4567"     | NULL
"813-123-4567"     | "1"
"813-123-4567"     | "0"
"813-123-4567"     | ""

CHAR_LENGTH(phone2) > 0 Results (same)

users
813-123-4567       | 1
813-123-4567       | 0

users2
813-123-4567       | 1
813-123-4567       | 0

---

Alternatives

phone2 <> '' Results (different)

users
813-123-4567       | 1

users2
813-123-4567       | 1
813-123-4567       | 0

phone2 > '' Results (different)

users
813-123-4567       | 1

users2
813-123-4567       | 1
813-123-4567       | 0

COALESCE(phone2, '') <> '' Results (same)
Note: the results differ from phone2 IS NOT NULL AND phone2 <> '' which is not expected

users
813-123-4567       | 1
813-123-4567       | 0

users2
813-123-4567       | 1
813-123-4567       | 0

phone2 IS NOT NULL AND phone2 <> '' Results (different)

users
813-123-4567       | 1

users2
813-123-4567       | 1
813-123-4567       | 0

Answer 5

To check if field is NULL use IS NULL, IS NOT NULL operators.

MySql reference http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html

Answer 6

If there are spaces in the phone2 field from inadvertant data entry, you can ignore those records with the IFNULL and TRIM functions:

SELECT phone, phone2
FROM jewishyellow.users
WHERE phone LIKE '813%'
    AND TRIM(IFNULL(phone2,'')) <> '';