Tạo bảng:
mysql> create table DemoTable -> ( -> UserId int -> ); Query OK, 0 rows affected (0.48 sec)
Chèn dữ liệu mẫu:
mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(30); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values(30); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(40); Query OK, 1 row affected (0.21 sec)
Hiển thị dữ liệu:
mysql> select *from DemoTable;
Kết quả
+----------+ | UserId | +----------+ | 10 | | 20 | | 30 | | 10 | | 10 | | 20 | | 30 | | 10 | | 20 | | 20 | | 40 | +----------+ 11 rows in set (0.00 sec)
Truy vấn đếm số giá trị xuất hiện ≥ 3 lần:
mysql> select count(*) -> from (select UserId, count(*) as total -> from DemoTable group by UserId -> )tbl -> where total >=3;
Kết quả: Giá trị 10 và 20 xuất hiện ≥ 3 lần, nên đếm được 2 giá trị.
Kết quả
+----------+ | count(*) | +----------+ | 2 | +----------+ 1 row in set (0.01 sec)