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更新时间：2024-10-10 GMT+08:00
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GaussDB(DWS)单表查询

示例表：

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CREATE TABLE newproducts
(
product_id INTEGER NOT NULL,
product_name VARCHAR2(60),
category VARCHAR2(60),
quantity  INTEGER
)
WITH (ORIENTATION = COLUMN) DISTRIBUTE BY HASH(product_id);


INSERT INTO newproducts VALUES (1502, 'earphones', 'electronics',150);
INSERT INTO newproducts VALUES (1601, 'telescope', 'toys',80);
INSERT INTO newproducts VALUES (1666, 'Frisbee', 'toys',244);
INSERT INTO newproducts VALUES (1700, 'interface', 'books',100);
INSERT INTO newproducts VALUES (2344, 'milklotion', 'skin care',320);
INSERT INTO newproducts VALUES (3577, 'dumbbell', 'sports',550);
INSERT INTO newproducts VALUES (1210, 'necklace', 'jewels', 200);

简单查询

通过SELECT ... FROM ... 语句从数据库中获取结果。

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SELECT category FROM newproducts;
  category
------------
 electr
 sports
 jewels
 toys
 books
 skin care
 toys
(7 rows)

对结果进行筛选

通过WHERE语句对查询的结果进行过滤，找到想要查询的部分。

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SELECT * FROM newproducts WHERE category='toys';
 product_id | product_name | category | quantity
------------+--------------+----------+----------
       1601 | telescope    | toys     |       80
       1666 | Frisbee      | toys     |      244
(2 rows)

对结果进行排序

使用ORDER BY语句可以让查询结果按照期望的方式进行排序。

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SELECT product_id,product_name,category,quantity FROM newproducts ORDER BY quantity DESC;
 product_id | product_name |  category   | quantity
------------+--------------+-------------+----------
       3577 | dumbbell     | sports      |      550
       2344 | milklotion   | skin care   |      320
       1666 | Frisbee      | toys        |      244
       1210 | necklace     | jewels      |      200
       1502 | earphones    | electronics |      150
       1700 | interface    | books       |      100
       1601 | telescope    | toys        |       80
(7 rows)

限制结果查询数量

如果需要查询只返回部分结果，可以使用LIMIT语句限制查询结果返回的记录数。

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SELECT product_id,product_name,category,quantity FROM newproducts ORDER BY quantity DESC limit 5;
 product_id | product_name |  category   | quantity
------------+--------------+-------------+----------
       3577 | dumbbell     | sports      |      550
       2344 | milklotion   | skin care   |      320
       1666 | Frisbee      | toys        |      244
       1210 | necklace     | jewels      |      200
       1502 | earphones    | electronics |      150
(5 rows)

聚合查询

可以通过使用GROUP BY语句配合聚合函数，构建一个聚合查询来关注数据的整体情况。

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SELECT category, string_agg(quantity,',') FROM newproducts group by category;
  category   | string_agg
-------------+------------
 toys        | 80,244
 books       | 100
 sports      | 550
 jewels      | 200
 skin care   | 320
 electronics | 150

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