数据库---查询(详细)

1、查询
SELECT * FROM 表名 WHERE 条件；
(1)、SELECT * FROM 表名；                               #查询表内的所有数据
SELECT * FROM PRODUCT;


(2)、SELECT 字段1，字段2... FROM 表名;                  #查询表内的指定字段的数据
SELECT PIN,PRICE FROM PRODUCT;        


(3)、SELECT * FROM 表名 AS 别名;                           #表别名查询
SELECT * FROM PRODUCT AS p;     


(4)、SELETE 字段名 AS 别名,字段名 AS 别名...FROM 表名;          #字段别名查询，并显示别名
SELECT PID AS '编号',PNAME AS '品牌' FROM PRODUCT;


(5)、SELECT DISTINCT 字段 FROM 表名;                   #查询指定字段并去除重复值
SELECT DISTINCT CATEGORY_ID FROM PRODUCT;

(6)、SELECT 字段+值 FROM 表名;                      #运算查询：查询指定字段并给该字段进行运算
SELECT PRICE+10 FROM PRODUCT;


(7)、SELECT * FROM 表名 WHERE 条件;                  #查询符合条件的所有字段
SELECT * FROM PRODUCT WHERE PNAME='花花公子';          #查询PNAME是花花公子的所有product信息
SELECT * FROM PRODUCT WHERE PRICE=800;          #查询PRICE是800的所有product信息
SELECT * FROM PRODUCT WHERE PRICR!=800;          #查询price不是800的所有product信息
SELECT * FROM PRODUCT WHERE NOT(PRICE=800);          #同上
SELETE * FROM PRODUCT WHERE PRICE<>800;          #同上
SELECT * FROM PRODUCT WHERE PRICE>60;         #查询price大于60的所有product信息
SELECT * FROM PRODUCT WHERE PRICE BETWEEN 200 AND 1000;                 #查询price在200到1000之间的所有product信息
SELECT * FROM PRODUCT WHERE PRICR>=200 AND PRICE<=1000;         #同上
SELECT * FROM PRODUCT WHERE PRICE=200 OR PRICE=800;          #查询price是200或是800的所有product信息
SELECT * FROM PRODUCT WHERE PNAME LIKE '%霸%';         #查询pname中包含‘霸’的所有product信息
SELECT * FROM PRODUCT WHERE PNAME LIKE '香%';         #查询pname中以‘香’开头的所有product信息
SELECT * FROM PRODUCT WHERE PNAME LIKE '_想%';                 #查询pname中第二个字是‘想’的所有product信息
SELECT * FROM PRODUCT WHERE CATEGORY_ID IS NULL; #查询category_id为空的所有product信息
SELECT * FROM PRODUCT WHERE CATEGORY_ID IS NOT NULL; #查询category_id不为空的所有product信息


(8)、SELECT * FROM 表名 ORDER BY 字段 ASC|DESC;              #查询表内所有信息并按指定字段进行排序(ASC:升序、DESC:降序)，排序默认升序(ASC)
SELECT * FROM PRODUCT ORDER BY PRICE DESC;         #查询表内所有信息并按price字段进行降序排列
SELECT * FROM PRODUCT ORDER BY PRICE DESC,CATEGORY_ID DESC; #查询表内所有信息在price降序排列的基础上再对category_id进行降序排列