PostgreSQL：使用for循环迭代表行，根据当前行检索列值

我有以下2张表

CREATE TABLE salesperson_t (
    salespersonid numeric(4,0) NOT NULL,
    salespersonname character varying(25),
    salespersontelephone character varying(50),
    salespersonfax character varying(50),
    salespersonaddress character varying(30),
    salespersoncity character varying(20),
    salespersonstate character(2),
    salespersonzip character varying(20),
    salesterritoryid numeric(4,0),
    CONSTRAINT salesperson_pk PRIMARY KEY (salespersonid)
);

INSERT INTO salesperson_t VALUES (1, 'Doug Henny', '8134445555', NULL, NULL, NULL, NULL, NULL, 2);
INSERT INTO salesperson_t VALUES (2, 'Robert Lewis', '8139264006', NULL, '124 Deerfield', 'Lutz', 'FL', '33549', 13);
INSERT INTO salesperson_t VALUES (3, 'William Strong', '3153821212', NULL, '787 Syracuse Lane', 'Syracuse', 'NY', '33240', 3);
INSERT INTO salesperson_t VALUES (4, 'Julie Dawson', '4355346677', NULL, NULL, NULL, NULL, NULL, 4);
INSERT INTO salesperson_t VALUES (5, 'Jacob Winslow', '2238973498', NULL, NULL, NULL, NULL, NULL, 5);
INSERT INTO salesperson_t VALUES (6, 'Pepe Lepue', NULL, NULL, NULL, 'Platsburg', 'NY', NULL, 13);
INSERT INTO salesperson_t VALUES (8, 'Fred Flinstone', NULL, NULL, '1 Rock Lane', 'Bedrock', 'Ca', '99999', 2);
INSERT INTO salesperson_t VALUES (9, 'Mary James', '3035555454', NULL, '9 Red Line', 'Denver', 'CO', '55555', 4);
INSERT INTO salesperson_t VALUES (10, 'Mary Smithson', '4075555555', NULL, '4585 Maple Dr', 'Orlando', 'FL', '32826', 15);

CREATE TABLE territory2_t (
    territoryid numeric(4,0),
    territoryname character varying(50),
    total_sales_person integer,
    CONSTRAINT territory2_t_pk PRIMARY KEY (territoryid)
);

INSERT INTO territory2_t VALUES (1, 'SouthEast', NULL);
INSERT INTO territory2_t VALUES (2, 'SouthWest', NULL);
INSERT INTO territory2_t VALUES (3, 'NorthEast', NULL);
INSERT INTO territory2_t VALUES (4, 'NorthWest', NULL);
INSERT INTO territory2_t VALUES (5, 'Central', NULL);
INSERT INTO territory2_t VALUES (6, 'Alaska', NULL);
INSERT INTO territory2_t VALUES (12, 'Hawaii', NULL);
INSERT INTO territory2_t VALUES (13, 'Colorado', NULL);
INSERT INTO territory2_t VALUES (15, 'Arizona', NULL);

我有以下伪代码：

DO $$
DECLARE
    -- currentRow [relevant datatype];
BEGIN
    FOR counter IN 1..(SELECT count(*)FROM territory2_t) LOOP -- There are 13 total rows

        -- **assign currentRow to counter**

        RAISE NOTICE 'Counter: %', counter; -- debugging purposes

        UPDATE terriory2_t
        SET total_sales_person = ((SELECT count(*)
                                    FROM salesperson_t
                                    WHERE salesterritoryid = currentRow.territoryid)*1) -- *1 is for debuggin puporses
        WHERE territoryid = currentRow.territoryid;

        -- **increase currentRow by 1**
    END LOOP;
END; $$

其目的是计算表（销售人员）中有多少行具有 currentRows->'territory2.territoryid' 的 'territoryid'，然后将该数量分配给 currentRows->territory2.total_sales_person。

为此，您不需要循环，甚至不需要函数。

您想要做的事情可以在单个更新语句中完成，因为每个区域的总计数可以通过单个聚合来计算：

SELECT salesterritoryid, count(*) as total_count
FROM salesperson_t
group by salesterritoryid

然后可以将其用作更新区域表的源：

UPDATE territory2_t
   SET total_sales_person = t.total_count
FROM (
   SELECT salesterritoryid, count(*) as total_count
   FROM salesperson_t
   group by salesterritoryid
) t 
WHERE territoryid = t.salesterritoryid;

另一种可能更容易理解但对于较大的表来说会更慢的替代方案是使用相关子查询进行更新

UPDATE territory2_t tg
   SET total_sales_person = (select count(*) 
                             from salesperson_t sp
                             where sp.salesterritoryid = tg.territoryid);

第一次和第二次更新之间有细微的差别：第二次更新会将total_sales_person更新为0（零）对于根本没有销售人员的地区。第一个只会更新销售人员表中实际存在的区域的计数。

^{Unrelated, but: having a "type identifying" prefix or suffix for an identifier is usually useless and doesn't really help at all. See a related discussion on dba.stackexchange https://dba.stackexchange.com/questions/154251/is-adding-the-tbl-prefix-to-table-names-really-a-problem}