How to use a dynamically created column in a WHERE clause - sql

Question

I created a table column called name cause the firstname and the lastname are stored in two separate columns. To solve the problem I use CONCAT in the SELECT statement. However if I want to search for a specific value inside the name column SQL returns the error:
Unknown column 'name' in 'where clause'
Is it possible to search in a dynamically created column in a SELECT statement?
SELECT
u.ID AS id,
CONCAT(umFirstName.meta_value, " ", umLastName.meta_value) AS name,
u.user_email AS email,
umChatStatus.meta_value AS chatStatus,
umCallStatus.meta_value AS callStatus,
umRef.meta_value AS reference
FROM
wp_users AS u
LEFT JOIN
wp_usermeta AS um ON u.ID = um.user_id
LEFT JOIN
wp_usermeta AS umFirstName ON u.ID = umFirstName.user_id
AND umFirstName.meta_key = "_ctbFirstName"
LEFT JOIN
wp_usermeta AS umLastName ON u.ID = umLastName.user_id
AND umLastName.meta_key = "_ctbLastName"
LEFT JOIN
wp_usermeta AS umChatStatus ON u.ID = umChatStatus.user_id
AND umChatStatus.meta_key = "_ctbChatSessionStatus"
LEFT JOIN
wp_usermeta AS umCallStatus ON u.ID = umCallStatus.user_id
AND umCallStatus.meta_key = "_ctbCallSessionStatus"
LEFT JOIN
wp_usermeta AS umRef ON u.ID = umRef.user_id
AND umRef.meta_key = "_ctbRef"
WHERE
um.meta_key = "wp_capabilities"
AND um.meta_value IN ('a:1:{s:8:"employee ";b:1;}')
AND u.id LIKE '%%'
OR name LIKE '%%'
OR u.user_email LIKE '%%'
OR umChatStatus.meta_value LIKE '%%'
OR umCallStatus.meta_value LIKE '%%'
OR umRef.meta_value LIKE'%%'
ORDER BY
id DESC
LIMIT 0, 20
UPDATE
Got it working like it should. Thanks to Caius Jard metioning to -always use parentheses- in a AND and OR mix. For someone that is interested in the solution.

Answer 1

SQL queries are evaluated in the following order (just the blocks you've used):
FROM (including joins)
WHERE
SELECT
ORDER BY
This means that something you create in the SELECT, like CONCAT(Firstname, ' ', LastName) simply doesn't exist at the time the WHERE is evaluated
You have a couple of options:
Use CONCAT(Firstname, ' ', LastName) in the WHERE clause too
SELECT
CONCAT(Firstname, ' ', LastName) AS N
FROM
person
WHERE
CONCAT(Firstname, ' ', LastName) = 'John smith'
Turn the whole query into a sub query and use the thing you created in the outer
SELECT
x.N
FROM
(
SELECT
CONCAT(Firstname, ' ', LastName) AS N
FROM
person
) x
WHERE
x.N = 'John smith'
This form can also be written as:
WITH x AS
(
SELECT
CONCAT(Firstname, ' ', LastName) AS N
FROM
person
)
SELECT x.N
FROM x
WHERE x.N = 'John smith'
These latter forms are useful when you want to use it multiple times and don't want to keep repeating some massive calculation:
WITH x AS
(
SELECT
SUM(Points) / DATEDIFF(day, MIN(GameStart), MAX(GameEnd)) as PointsPerDay
FROM
Games
GROUP BY PlayerId
)
SELECT
CASE
WHEN PointsPerDay < 100 THEN 'Newbie'
WHEN PointsPerDay < 200 THEN 'Seasoned'
WHEN PointsPerDay < 300 THEN 'Advanced'
ELSE 'Pro'
END as Grading
FROM x
To have to keep repeating a calculation in order to do it all in one query is a bit ugly:
SELECT
CASE
WHEN SUM(Points) / DATEDIFF(day, MIN(GameStart), MAX(GameEnd)) < 100 THEN 'Newbie'
WHEN SUM(Points) / DATEDIFF(day, MIN(GameStart), MAX(GameEnd)) < 200 THEN 'Seasoned'
WHEN SUM(Points) / DATEDIFF(day, MIN(GameStart), MAX(GameEnd)) < 300 THEN 'Advanced'
ELSE 'Pro'
END as Grading
FROM
Games
GROUP BY PlayerId
And indeed because a GROUP BY is evaluated after a WHERE, if you want to use the result of a group by in a where you must do it as a "sub query that groups"/"outer query that wheres" pair

Answer 2

You can directly compare the concatenated value in the where clause like so:
CONCAT(umFirstName.meta_value, " ", umLastName.meta_value) LIKE '%abc%'
SELECT
u.ID AS id,
CONCAT(umFirstName.meta_value, " ", umLastName.meta_value) AS name,
u.user_email AS email,
umChatStatus.meta_value AS chatStatus,
umCallStatus.meta_value AS callStatus,
umRef.meta_value AS reference
FROM wp_users AS u
LEFT JOIN wp_usermeta AS um ON u.ID = um.user_id
LEFT JOIN wp_usermeta AS umFirstName ON u.ID = umFirstName.user_id AND
umFirstName.meta_key = "_ctbFirstName"
LEFT JOIN wp_usermeta AS umLastName ON u.ID = umLastName.user_id AND
umLastName.meta_key = "_ctbLastName"
LEFT JOIN wp_usermeta AS umChatStatus
ON u.ID = umChatStatus.user_id AND umChatStatus.meta_key = "_ctbChatSessionStatus"
LEFT JOIN wp_usermeta AS umCallStatus
ON u.ID = umCallStatus.user_id AND umCallStatus.meta_key = "_ctbCallSessionStatus"
LEFT JOIN wp_usermeta AS umRef ON u.ID = umRef.user_id AND umRef.meta_key = "_ctbRef"
WHERE um.meta_key = "wp_capabilities"
AND um.meta_value IN ('a:1:{s:8:"employee ";b:1;}')
AND u.id LIKE '%%'
OR CONCAT(umFirstName.meta_value, " ", umLastName.meta_value) LIKE '%%'
OR u.user_email LIKE '%%'
OR umChatStatus.meta_value LIKE '%%'
OR umCallStatus.meta_value LIKE '%%'
OR umRef.meta_value LIKE'%%'
ORDER BY id DESC
LIMIT 0, 20