Question

最近我发现SQLite不支持看似postgresql特定的DISTINCT ON()子句。例如，如果我的表t包含列a和b。我想选择具有不同b的所有项目。在SQLite中，以下查询是唯一一种正确的方法吗？

select * from t where b in (select distinct b from t)

示例数据：

a | b
__|__
1   5
2   5
3   6
4   6

我期待的回报：

a | b
__|__
1   5
3   6

Answer 1

sqlite> SELECT * FROM t GROUP BY b;
2|5
4|6
(for each b: one (unpredictable) value of a)

sqlite> SELECT * FROM (SELECT * FROM t ORDER BY a DESC) GROUP BY b;
1|5
3|6
(for each b: the row with min a)

sqlite> SELECT * FROM (SELECT * FROM t ORDER BY a ASC) GROUP BY b;
2|5
4|6
(for each b: the row with max a)

Answer 2

使用：

  SELECT MIN(t.a) AS A,
         t.b
    FROM TABLE t
GROUP BY t.b

SQLite中的DISTINCT子句

2 个答案: