# 查询

SELECT * from "user_info" where "id" = 2;
SELECT * from "user_info" where "user_info"."id" = 2;

# 更新

/* 下面sql执行会报错 > ORA-00942: table or view does not exist */
/* 原因就是oracle数据库是区分大小写的，而且oracle的默认为大写的，也就是说在sql脚本上面写的sql语句，oracle运行的时候，它会自动转化为大写，参考 https://www.cnblogs.com/javJoker/p/7069321.html*/
update user_info set password = "666" where id = 3;

/* 把表名和字段名都加上双引号来区分大小写 */
/* 加上双引号后执行报错 > ORA-00904: "666": invalid identifier */
/* 解决方法就是把666这个值改为单引号，原因是 password字段的类型为VARCHAR2，只能用单引号 */
update "user_info" set "password" = "666" where "id" = 3;

/* 正常sql */
update "user_info" set "password" = '777' where "id" = 3;

# 插入

/* > ORA-00984: column not allowed here 原因是 username和password字段的类型为VARCHAR2，只能用单引号把值包起来 */
INSERT INTO "user_info" ("id","username","password") VALUES (4,"ccc",'111111');

/* 正常sql */
INSERT INTO "user_info" ("id","username","password") VALUES (4,'ccc','111111');

# 删除

/* as 别名问题，执行报错 > ORA-00933: SQL command not properly ended ，原因就是oracle里不需要as关键词，直接空格+别名即可 */
DELETE from "user_info" as ui where ui."id" = 4;

/* 正常sql */
delete from "user_info" where "id" = 4;
DELETE from "user_info" ui where ui."id" = 4;