MySQL Orderby a number, Empty Strings (or 0’s) Last

MySQLsql-order-by

Just asked a question pretty similar to this one…

Currently I am doing a very basic OrderBy in my statement.

SELECT * FROM tablename WHERE visible=1 ORDER BY position ASC, id DESC

The problem with this is that empty string entries for 'position' are treated as 0. Therefore all entries with position as empty string appear before those with 1,2,3,4. eg:

'', '', '', 1, 2, 3, 4

or:

0, 0, 0, 1, 2, 3, 4

Is there a way to achieve the following ordering:

1, 2, 3, 4, '', '', ''.

or:

1, 2, 3, 4, 0, 0, 0.

I assume the solution may have some kind of replace function but I am not able to find a function which does what I am after.

Best Answer

SELECT * 
FROM tablename 
WHERE visible=1 
ORDER BY 
    case when position in('', '0') then 1 else 0 end,
    position ASC, 
    id DESC

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You can use GROUP_CONCAT:

SELECT person_id,
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FROM peoples_hobbies
GROUP BY person_id;

As Ludwig stated in his comment, you can add the DISTINCT operator to avoid duplicates:

SELECT person_id,
   GROUP_CONCAT(DISTINCT hobbies SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

As Jan stated in their comment, you can also sort the values before imploding it using ORDER BY:

SELECT person_id, 
       GROUP_CONCAT(hobbies ORDER BY hobbies ASC SEPARATOR ', ')
FROM peoples_hobbies
GROUP BY person_id;

As Dag stated in his comment, there is a 1024 byte limit on the result. To solve this, run this query before your query:

SET group_concat_max_len = 2048;

Of course, you can change 2048 according to your needs. To calculate and assign the value:

SET group_concat_max_len = CAST(
                     (SELECT SUM(LENGTH(hobbies)) + COUNT(*) * LENGTH(', ')
                           FROM peoples_hobbies
                           GROUP BY person_id) AS UNSIGNED);

Mysql – Which MySQL data type to use for storing boolean values

For MySQL 5.0.3 and higher, you can use BIT. The manual says:

As of MySQL 5.0.3, the BIT data type is used to store bit-field values. A type of BIT(M) enables storage of M-bit values. M can range from 1 to 64.

Otherwise, according to the MySQL manual you can use BOOL or BOOLEAN, which are at the moment aliases of tinyint(1):

Bool, Boolean: These types are synonyms for TINYINT(1). A value of zero is considered false. Non-zero values are considered true.

MySQL also states that:

We intend to implement full boolean type handling, in accordance with standard SQL, in a future MySQL release.

References: http://dev.mysql.com/doc/refman/5.5/en/numeric-type-overview.html

Best Answer

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Mysql – Which MySQL data type to use for storing boolean values

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