ccodes.net
专注资源分享

PostgreSQL 实现子查询返回多行的案例

 

作为一个表达式使用的子查询返回了多列:在查询中,我们需要以第2条查询语句作为第一条查询语句的条件,但是第一条根据这个条件查询出来是多个数据,这时候又需要保留多个数据,运用子查询就会报错,以下就为解决这种多对多关系查询,且没有关联关系的表的解决方案:select c.rain_value,c.ad_nm from
(
select *, json::json->t2.lon_lat as rain_value from actual_time_model_json t1,
(SELECT DISTINCT lon || ‘_’ || lat as lon_lat,ad_nm from grid_all_points_null)t2 where section=’0′ and t1.filename = ‘Z_NWGD_C_BCCD_20180711022009_P_RFFC_SPCC-ER01_201807110800_02401.GRB2’
)c where c.rain_value is not null 补充:PostgreSQL 的子查询 相关的知识 ,exists,any,allSubquerySELECT
 film_id,
 title,
 rental_rate
FROM
 film
WHERE
 rental_rate > (
  SELECT
   AVG (rental_rate)
  FROM
   film
 ); 有了子查询,在设定 需要查询表才能得到 查询条件时,就可以 直接 在一条语句中 写,不用分开多条写了,方便了许多。子查询返回多条时,可以在 where 子句中 用 IN,来匹配查询条件。SELECT
 film_id,
 title
FROM
 film
WHERE
 film_id IN (
  SELECT
   inventory.film_id
  FROM
   rental
  INNER JOIN inventory ON inventory.inventory_id = rental.inventory_id
  WHERE
   return_date BETWEEN ‘2005-05-29’
  AND ‘2005-05-30’
 ); EXISTS 操作符在 where 子句的 查询条件中,exists 操作符,会在子查询有返回行时,返回true;不论返回几行。因此,子查询中的查询字段仅写1就好;标准的写法:EXISTS (SELECT 1 FROM tbl WHERE condition)SELECT
 first_name,
 last_name
FROM
 customer
WHERE
 EXISTS (
  SELECT
   1
  FROM
   payment
  WHERE
   payment.customer_id = customer.customer_id
 ); NO EXISTS ,与之相反,当子查询返回0行时,返回trueSELECT first_name,
  last_name
FROM customer c
WHERE NOT EXISTS
 (SELECT 1
  FROM payment p
  WHERE p.customer_id = c.customer_id
  AND amount > 11 )
ORDER BY first_name,
   last_name; 当子查询返回 NULL,会返回true, 也就是返回所有行。SELECT
 first_name,
 last_name
FROM
 customer
WHERE
 EXISTS( SELECT NULL )
ORDER BY
 first_name,
 last_name; ANY与任何子查询返回的 值 匹配就 返回 trueexpresion operator ANY(subquery)表达式一般为 字段操作符为 >,<,=,<>,>=,<=ANY 可以与 SOME 替换子查询 返回的 必须是 一列,SELECT title
FROM film
WHERE length >= ANY(
 SELECT MAX( length )
 FROM film
 INNER JOIN film_category USING(film_id)
 GROUP BY category_id ); The = ANY is equivalent to IN operator.Note that the <> ANY operator is different from NOT IN. The following expression:1x <> ANY (a,b,c)is equivalent to1x <> a OR x <> b OR x <> cALL所有子查询返回的值 匹配 则 返回 true也就是 大于最大,小于最小SELECT
 film_id,
 title,
 length
FROM
 film
WHERE
 length > ALL (
   SELECT
    ROUND(AVG (length),2)
   FROM
    film
   GROUP BY
    rating
 )
ORDER BY
 length;文章

'); })();