sql - 添加一个汇总行，其中包含每个子句的总计

Question

我不知道如何制作这个 sql select 语句，我使用 PostgreSQL 数据库。 这是我的表格:

我想添加一个额外的行来显示按性别划分的客户数量:

这可以做到吗？

Answer 1

您可以使用GROUP BY GROUPING SETS (Postgresql 9.5+):

CREATE TABLE customers(idcust INT, name VARCHAR(100), fkGender INT);
INSERT INTO customers(idcust, name, fkGender)
SELECT 1, 'bob', 3 UNION ALL SELECT 2, 'alice', 3  UNION ALL SELECT 3, 'mikel', 4;

CREATE TABLE gender(IdGender INT, gender VARCHAR(100));
INSERT INTO gender(IdGender, gender) VALUES (3, 'male'),(4,'female');

-------------------------------------------------------------------------------------
SELECT CASE WHEN idcust::text IS NULL THEN 'Total' ELSE idcust::text END AS IdCust,
       CASE WHEN name IS NOT NULL THEN name ELSE COUNT(*)::text END AS name,
       CASE WHEN idcust::text IS NULL THEN '' ELSE gender END AS genderName
FROM customers c
JOIN gender g
  ON c.fkGender = g.idGender
GROUP BY GROUPING SETS((idcust, name, gender), (gender))
ORDER BY gender DESC, idcust;

输出:

请记住，idcust 可能是 INT，因此要在该列中获取 Total，您必须先转换为文本。