从x表中选择所有不在y表的column_foo中的ID

Question

How do I select all IDs from table_x that are not present in any row of table y in column_foo ?

I'm struggling to do this with a single SQL query.

Answer 1

SELECT id FROM x
  WHERE NOT EXISTS (SELECT * FROM y WHERE foo = id)

Or

SELECT id FROM x
  WHERE id NOT IN (SELECT foo FROM y)

Or if y.foo is not a nullable column, you can even do:

SELECT x.id FROM x
  LEFT JOIN y ON x.id = y.foo
  WHERE y.foo IS NULL

Answer 2

也许您可以执行以下操作：

SELECT id FROM table_x WHERE id NOT IN (SELECT column_foo FROM table_y);

Answer 3

You would use a LEFT JOIN. More explanation and examples here.

Visual Joins

Answer 4

It's better to avoid subqueries if you can. An INNER JOIN will return only rows that meet the join criteria.

SELECT DISTINCT
    x.id
FROM
    table_x x
    INNER JOIN table_y y ON (x.id = y.id_column_in_y)