如何计算表中某列中具有相同值的行数？

Question

假设我有以下简单表格：

create table mytable (
    desid bigint not null,
    ancid bigint not null
  );

insert into mytable (ancid,desid) values (1,10);
insert into mytable (ancid,desid) values (1,20);
insert into mytable (ancid,desid) values (1,21);
insert into mytable (ancid,desid) values (1,22);
insert into mytable (ancid,desid) values (2,30);
insert into mytable (ancid,desid) values (3,40);
insert into mytable (ancid,desid) values (3,41);
insert into mytable (ancid,desid) values (3,42);
insert into mytable (ancid,desid) values (3,43);

什么是 SQL 命令将打印出以下信息：

4 rows with ancid=1
1 rows with ancid=2
4 rows with ancid=3

Answer 1

您可以通过按ancid分组来获取信息：

SELECT   ancid, COUNT(*)
FROM     mytable
GROUP BY ancid