Laravel连接并从多个表中进行选择

Question

So I have Laravel 5.2 and in my SQL database I have several tables: books with fields title, author and year, journals with fields title, year and price newspapers with fields title, town, year

I need to get a list of all titles from all three tables, where the year is 1994. I've tried to do the following

$titles = DB::table('books')->where('books.year', 1994)->leftjoin('journals as journals', 'books.year', '=', 'journals.year')->leftjoin('newspapers as newspapers', 'books.year', '=', 'newspapers.year')->select('books.title', 'journals.title', 'newspapers.title')->get();

But with this query I get entries full of nulls, and only newspapers are filled in. What am I doing wrong?

Answer 1

In this case (if the tables are not related) you should use union, no join.

$books = DB::table('books')->select('title')->where('year', 1994);
$journals = DB::table('journals')->select('title')->where('year', 1994);
$titles = DB::table('newspapers')->select('title')->where('year', 1994)->union($books)->union($journals)->get();