检查列中的多个值以查找 MySQL 中的条件

Question

I have a table like:

person    product
P1        A
P1        B
P1        C
P2        A
P2        B
P2        D
P3        A

I need to write a SQL query to select person who uses product A and B, but not the product C.

I tried using AND and IN operator, but it obviously shouldnt work as the result is expecting it to be.

Here the expected result is:

P2

Answer 1

SELECT person
FROM source_table
GROUP BY person
HAVING SUM(product = 'A')      -- at least one
   AND SUM(product = 'B')      -- at least one
   AND NOT SUM(product = 'C')  -- strictly none

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Comparing result is treated as 1 when matched (is TRUE) and as 0 when not matched (is FALSE). So SUMs in HAVING simply counted rows in a group which matches the condition.

Of course full condition form needs SUM(product = 'A') > 0 and SUM(product = 'C') = 0 . But MySQL treates zero as FALSe and any non-zero as TRUE, so additional compare is excess.

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This technique allows you to create more complex conditions. For example:

• at least one A or B: SUM(product IN ('A', 'B'))
• at least two from the list A,B,C: SUM(product IN ('A', 'B', 'C')) >= 2
• 2 or 3 from the list A,B,C,D: SUM(product IN ('A', 'B', 'C', 'D')) BETWEEN 2 AND 3

and so on...

Answer 2

you could use something like this:

SELECT person, GROUP_CONCAT(product) AS all_products
FROM mytable
GROUP BY person
HAVING all_products REGEXP ('A') 
AND all_products REGEXP ('B')
AND all_products NOT REGEXP ('C');