MySQL SELECT COUNT（*）基于多个条件的两个表

Question

I have some sort of logic/sql challenge. I have two tables that hold user data and are related by a id. I would like to select the count of rows based on conditions from the two tables.

Here are my tables.

table one

t_contacts
id  | name    | tel     | profession | email   | sex  | city    | state   |
int | varchar | varchar | int        | varchar | char | varchar | varchar |

table two

t_contacts_meta
cid                | interest     |
int (t_contact_id) | varchar      |

from the table, contacts are stored on the t_contacts table and their interest stored on the t_contacts_meta table. One contact could have multiple interests.

My issue is the SQL query. example

 SELECT COUNT(*) as count 
 FROM t_contacts 
 where `state`='$state' 
    AND `profession`='$profession' 
    AND `sex`='$sex' 
    AND (
        `t_contacts_meta.interest`='$interest_1' 
        OR `t_contacts_meta.interest`='$interest_2 
        OR `t_contacts_meta.interest`='$interest_n'
    )

The sql i provided above is not my working code its just an example. I dont even know how to go about the query.

Thanks for the help :)

Answer 1

You need to join the tables first:

SELECT COUNT(c.id) as count 
FROM t_contacts c
inner join t_contacts_meta m on m.cid = c.id
where 
(c.state=$state) AND 
(c.profession=$profession) AND 
(c.sex=$sex) AND 
(m.interest=$interest_1 OR m.interest=$interest_2 OR m.interest=$interest_n)

Answer 2

This is you're probably looking for:

SELECT COUNT(C.id) AS [count]
FROM t_contacts C
INNER JOIN t_contacts_meta M ON M.cid = C.id
                               AND M.interest IN ('interest_1', 'interest_2', 'interest_n')
WHERE C.state = 'state_value'
    AND C.profession = 'profession_value'
    AND C.sex = 'sex_value'

Hope this will help you.

Answer 3

这不是逻辑挑战，您需要学习如何联接表

SELECT count(*) as count from t_contacts as T LEFT JOIN t_contacts_meta as M ON t.id=M.id WHERE T.state='$state' ...

Answer 4

You would use a join. Your query will work if you use the following join in your query:

SELECT COUNT(t_contacts.id) as count FROM t_contacts LEFT JOIN t_contacts_meta ON t_contacts_meta.cid = t_contacts.id WHERE `state`='$state' AND `profession`='$profession' AND `sex`='$sex' AND (`t_contacts_meta.interest`='$interest_1' OR `t_contacts_meta.interest`='$interest_2 OR `t_contacts_meta.interest`='$interest_n')

I did not test this query, but you will at least get the idea, good luck!

Answer 5

To get a count of just rows from t_contacts, and not "count" any row from t_contacts more than once...

One approach is to use an EXISTS predicate with a correlated subquery, eg

SELECT COUNT(*)
  FROM t_contacts t
 WHERE t.state      = 'fee'
   AND t.profession = 'fi'
   AND t.sex        = 'fo'
   AND EXISTS ( SELECT 1
                  FROM t_contacts_meta m 
                 WHERE m.cid = t.id
                   AND m.interest IN ('interest_1', 'interest_2', 'interest_n')
              )

An alternate approach is to use a JOIN operation, and count the "distinct" rows from t_contacts . Assuming that the id column is the PRIMARY KEY of the table (or is at least guaranteed to be unique and not null.)

Note the use of the DISTINCT keyword inside the COUNT aggregate)

SELECT COUNT(DISTINCT t.id)
  FROM t_contacts t
  JOIN t_contacts_meta m 
       ON m.cid = t.id
       AND m.interest IN ('interest_1', 'interest_2', 'interest_n')
 WHERE t.state      = 'fee'
   AND t.profession = 'fi'
   AND t.sex        = 'fo'

---

The original query appears to be including values of PHP variables in the SQL text, rather than using a prepared statement, eg

   `state`='$state' 

Note that this pattern is vulnerable to SQL Injection. Consider the actual SQL text if the value of $state contains a single quote, or contains something carefully constructed like:

    a' OR 'b'='b

Or something more nefarious, ala Little Bobby Tables

The normal pattern is to use the mysqli_real_escape_string function, to "escape" values included in SQL text.

http://php.net/manual/en/mysqli.real-escape-string.php

Answer 6

Try this

 SELECT COUNT(t_contacts_meta.interest) as count 
 FROM t_contacts_meta
 LEFT JOIN t_contacts
 ON t_contacts_meta.cid = t_contacts.id
 WHERE `t_contacts.state`='$state' 
    AND `t_contacts.profession`='$profession' 
    AND `t_contacts.sex`='$sex' 
    AND (
        `t_contacts_meta.interest`='$interest_1' 
        OR `t_contacts_meta.interest`='$interest_2 
        OR `t_contacts_meta.interest`='$interest_n'
    )