如何在Postgres中使用别名创建嵌套的SELECT COUNT

如何在Postgres中使用别名创建嵌套的SELECT COUNT

您要为每个字符创建一个单独的行。一种方法是生成所有字符，然后由它们聚合。这是一种方法：

select chr(chars.c + ascii('A')) as c,       sum(case when ascii(left(m.nome, 1)) = chars.c + ascii('A') then 1 else 0 end)from generate_series(0, 25) as chars(c) cross join     merchant mgroup by c;

编辑：

艾伦的建议是一个更好的查询：

select chr(chars.c + ascii('A')) as c,       count(m.nome)from generate_series(0, 25) as chars(c) left join     merchant m     on ascii(left(m.nome, 1)) = chars.c + ascii('A')group by c;