Ok, I think I might be overlooking something obvious/simple here... but I need to write a query that returns only records that match multiple criteria on the same column...
My table is a very simple linking setup for applying flags to a user ...
ID contactid flag flag_type ----------------------------------- 118 99 Volunteer 1 119 99 Uploaded 2 120 100 Via Import 3 121 100 Volunteer 1 122 100 Uploaded 2
etc... in this case you'll see both contact 99 and 100 are flagged as both "Volunteer" and "Uploaded"...
What I need to be able to do is return those contactid's ONLY that match multiple criteria entered via a search form...the contactid's have to match ALL chosen flags... in my head the SQL should look something like:
SELECT contactid WHERE flag = 'Volunteer' AND flag = 'Uploaded'...
but... that returns nothing... What am I doing wrong here?
Note – Use of IN for matching multiple values i.e. TOYOTA and HONDA in the same column i.e. COMPANY. Syntax: SELECT * FROM TABLE_NAME WHERE COLUMN_NAME IN (MATCHING_VALUE1,MATCHING_VALUE2);
You can use the OR condition in the WHERE clause to test multiple conditions where the record is returned if any one of the conditions are met. This example uses the WHERE clause to define multiple conditions, but instead of using the AND condition, it uses the OR condition.
The SQL AND condition and OR condition can be combined to test for multiple conditions in a SELECT, INSERT, UPDATE, or DELETE statement. When combining these conditions, it is important to use parentheses so that the database knows what order to evaluate each condition.
You can either use GROUP BY
and HAVING COUNT(*) = _
:
SELECT contact_id FROM your_table WHERE flag IN ('Volunteer', 'Uploaded', ...) GROUP BY contact_id HAVING COUNT(*) = 2 -- // must match number in the WHERE flag IN (...) list
(assuming contact_id, flag
is unique).
Or use joins:
SELECT T1.contact_id FROM your_table T1 JOIN your_table T2 ON T1.contact_id = T2.contact_id AND T2.flag = 'Uploaded' -- // more joins if necessary WHERE T1.flag = 'Volunteer'
If the list of flags is very long and there are lots of matches the first is probably faster. If the list of flags is short and there are few matches, you will probably find that the second is faster. If performance is a concern try testing both on your data to see which works best.
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