How to Correctly Find Players on a Team Within a Specific Year Range in PostgreSQL?

Finding Overlapping Date Ranges in PostgreSQL

You've provided a query that attempts to find all players who were on a specific team in a given year, but it's not working correctly. Let's address the issues you're facing and provide an alternative solution for finding overlapping date ranges.

Problems with the Original Query:

• The query incorrectly uses the BETWEEN operator to include the upper bound year, while most cases exclude it.
• The query doesn't check whether the players never left the team, which should also be included.

Correct Query:

To find all players of a given team who joined before 2010 and didn't leave before 2009, you can use the following query:

SELECT DISTINCT p.*
FROM team AS t
JOIN contract AS c ON t.name_team = c.name_team
JOIN player AS p ON c.name_player = p.name_player
WHERE t.name_team = ?
AND c.date_join < '2010-01-01'
AND c.date_leave >= '2009-01-01';

Additional Considerations:

• If your team table is only used for the join and doesn't add any necessary information, you can simplify the query by removing it.
• To handle players who may never have left the team (represented as NULL in date_leave), you can use an OR clause:

AND (c.date_leave >= '2009-01-01' OR c.date_leave IS NULL)

Using the OVERLAPS Operator:

PostgreSQL also provides the OVERLAPS operator, which can be used to find overlapping ranges. The following query uses OVERLAPS to find players who overlapped with the range '2009-01-01', '2010-01-01':

SELECT DISTINCT name_player
FROM contract
WHERE name_team = ?
AND (date_join, COALESCE(date_leave, CURRENT_DATE)) OVERLAPS
      ('2009-01-01', '2010-01-01');

Using a Range Type:

In PostgreSQL 9.2 or later, you can use a range type to represent date ranges. This provides better performance and allows for easier index support.

CREATE TYPE date_range AS RANGE (date, date);

CREATE INDEX mv_stock_dr_idx ON mv_stock USING gist (daterange(date_join, date_leave));

SELECT DISTINCT name_player
FROM contract
WHERE name_team = ?
AND daterange(date_join, date_leave) &&&
      daterange('[2009-01-01,2010-01-01)'); -- upper bound excluded

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