只选择一列不同的mysql

Question

I have 3 tables - users, journals, journaltags. I select data from 3 tables using chosen tags.

$sqltheme="SELECT users.id as uid, users.name, users.surname, users.avatar, journals.id, journals.author_id, journals.title, journals.text, journals.create_date, journaltags.name as jname FROM users
INNER JOIN journals ON users.id=journals.author_id
INNER JOIN journaltags ON journaltags.journal_id = journals.id WHERE journals.create_date LIKE ? AND journals.author_id=? AND (".$expression.") ORDER BY journals.id DESC LIMIT 10";
$stmtheme=$conn->prepare($sqltheme);
$stmtheme->execute($array);

But if two tags is the same for one journal then it is selected the same journal two times. How can I make DISTINCT journals.id. I tried GROUP BY journals.id but it didnt help.

Answer 1

If I understand correctly, your problem is that the journaltags table may have one or more rows with a duplicated journal_id and name column value, right? You can simply add a distinct clause to your select statement, after the word SELECT :

SELECT DISTINCT users.id as uid, users.name, users.surname, users.avatar, journals.id, journals.author_id, journals.title, journals.text, journals.create_date, journaltags.name as jname FROM users
INNER JOIN journals ON users.id=journals.author_id
INNER JOIN journaltags ON journaltags.journal_id = journals.id WHERE journals.create_date LIKE ? AND journals.author_id=? AND (".$expression.") ORDER BY journals.id DESC LIMIT 10

The reason that your GROUP BY journals.id did not work, is because you had other columns that needed to be included in the grouping as well. Adding distinct is essentially a short way of writing group by [all selected columns]