Reverse IN function - mysql

Question

Consider the following table teammessages:
15:10 | Peter | I'm off to the store, call my mobile phone if you need me.
15:11 | Susy | Have you seen the new scanner? It's lightning fast.
15:15 | Anne | We have an emergency here, John broke the tap! Please switch off the water supply!
15:15 | John | I did what?? :-D I'm in Vienna!
15:16 | Peter | I'm stuck in the elevator, help!
15:17 | Anne | I said WATER, not POWER supply!
When I want to SELECT the urgent messages, containing key words like "help" or "emergency", from that chaotic freetext, I would have to have a "reverse IN" function, which doesn't check if the field is IN a given list of alternatives (WHERE APPLECOLOR IN ('YELLOW', 'RED')) but which checks if a value of the given alternatives is IN the field (WHERE freetext REVERSE_IN ('help', 'emergency')).
I've tried constructs like WHERE freetext LIKE ('%help%' OR '%emergency%'), but this gives me empty results.
Clarification: I can do this with freetext LIKE ... OR freetext LIKE ... OR freetext LIKE ... but it gets very long. So I am just looking for a shorthand like IN is in the "reverse case" (APPLECOLOR = 'RED' OR APPLECOLOR = 'YELLOW' <=> APPLECOLOR IN ('RED', 'YELLOW')).

Answer 1

The correct form of your original query is:
WHERE freetext LIKE '%help%' OR freetext LIKE '%emergency%'
However you might also like to consider using MATCH. For that you will need to have a FULLTEXT index on the message column which you can add with this command:
ALTER TABLE teammessages ADD FULLTEXT INDEX(message);
You can then search using a query like this one:
SELECT *
FROM teammessages
WHERE MATCH(message) AGAINST('help emergency' IN BOOLEAN MODE)
which will give you better results than LIKE, which would also match words like 'whelp' or 'helpful' or 'helps'. In your sample table, this query returns:
time name message
15:15:00 Anne We have an emergency here, John broke the tap! Please switch off the water supply!
15:16:00 Peter I'm stuck in the elevator, help!
This query also has the advantage of not getting long as fast as multiple LIKEs

Answer 2

I suggest a Generated Column.
Answers involving LIKE are going to be very slow here, and answers involving full text search (freetext) expressions are telling MySql to index every word in the column, rather than just the words you care about.
You can use a generated column to produce a simple Y/N or 1/0 result for just the words you care about that only needs to evaluate the full column data at INSERT/UPDATE time.

Answer 3

You are probably looking for the words help and emergency. You don't want to find
Jake, your jokes are not helpful.
You must subtract the tax. Hope this helps :-)
So check whether your version of MySQL supports regular expressions where you can look for words:
select *
from teammessages
where freetext regexp '[[:<:]](help|emergency)[[:>:]]';
Rextester demo: http://rextester.com/ILROPQ12660

Answer 4

WHERE freetext LIKE ('%help%' OR '%emergency%') does not work like this.
It should be:
WHERE freetext LIKE '%help%' OR freetext LIKE '%emergency%'
Additional: From documentation of LIKE function:
With LIKE you can use the following two wildcard characters in the
pattern:
% matches any number of characters, even zero characters.
_ matches exactly one character.
mysql> SELECT 'David!' LIKE 'David_';
-> 1
mysql> SELECT 'David!' LIKE '%D%v%';
-> 1

Answer 5

you should try :
WHERE freetext LIKE('%help%') OR freetext LIKE('%emergency%')

Answer 6

You could find all messages that are urgent with keywords you know by doing something similar to this:
SELECT * FROM teammessages WHERE freetext LIKE '%help%' OR freetext LIKE '%emergency%';
You could do the 'reverse' of this by using NOT LIKE this way:
SELECT * FROM teammessages WHERE freetext NOT LIKE '%help%' AND freetext NOT LIKE '%emergency%';