至少两个匹配字段（mysql）

Question

I've got a query like:

SELECT * FROM table WHERE id=1 AND (field1=1 OR field2=1 OR field3=1 OR field4=1 OR field5=1 OR field6=1 OR field7=1 OR field8=1)

The actual query is longer and there are more than 25 fields in the brackets...

How would I make sure that at least two of the fields = 1? If those were rows it would be easy, but what about columns? Not sure if it's even possible.

Basically I need to run a php function only if there are at least two matching fields. The function then updates the selected fields so that they will not be selected again next time.

Answer 1

In MySQL, conditional statements can be evaluated directly, and they return "1" if they are true and "0" if they are false. So in this case, you can just sum the conditionals like so:

SELECT * FROM table WHERE id=1 AND (field1=1) + (field2=1) + (field3=1) + (...) >= 2

If the sum is equal to or greater than 2 then at least two fields have the value "1". Note that you must put parenthesis around the conditionals here to make sure they are individually evaluated; otherwise it doesn't parse correctly.

In the general case, there is also the MySQL's IF function. You could use it here like this:

SELECT * FROM table WHERE id=1 AND IF(field1=1, 1, 0) + IF(field2=1, 1, 0) + IF(field3=1, 1, 0) + (...) >= 2

IF() takes three arguments. The first is a condition. The second is the return value if the condition is true. The third is the return value if the condition is false. So this would work too since in MySQl, the value of a bare conditional is equivalent to the value of IF(conditional, 1, 0) .

Answer 2

Perhaps you could add another column or another table through a relation which would contain a count of those fields which contain the 1 value. Obviously there would then have to be some INSERT/UPDATE logic which either did this on every update to your existing table or was performed in a transaction: BEGIN UPDATE ... ; SELECT FROM table WHERE id=1 and fields_containing_one > 2; COMMIT (to insure isolation from any racing updates or inserts between your UPDATE logic and your desired query.

I'm tacitly assuming that your fieldN values can be numbers other than 0 and 1 and that you are looking only for those which are precisely == 1. If you know that the fieldN values are only 0 or 1 then you could probably work with just a SUM of all the fieldN values.

Overall it sounds like your table/schema is denormalized and that's likely to cause other issues as you continue to work with this database. Rather than having field1, field2, ... for each row of your data set you could probably normalize the schema by having two columns (field_num or attribute_name and the corresponding value). Then instead of one row with N fields for a given entity you'd have N rows for each entity ... one for every (KEY)+(fieldN,value) tuple.

Under that schema you might add the constraint UNIQUE (whatever your existing key is + field_name) (to ensure that each entity has no more than one of each type of "field_name" rows).

If that were your schema then you could do something like: SELECT id FROM (SELECT table WHERE id=1 AND value=1) WHERE COUNT(id) > 1 (in other words use a sub-SELECT clause in your query.

Answer 3

通过将fields ... 8加在一起，看看结果是否等于2应该可以解决问题。