php 检查mysql表的列中是否存在值
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Check if a value exists in a column in mysql table
提问by user870380
I have a table called accountinfo with a row called username.
我有一个名为 accountinfo 的表，其中一行名为 username。
When i run the register.php i want to check if the username already exists in the mysql table or not.
当我运行 register.php 时，我想检查用户名是否已经存在于 mysql 表中。
Anyone have any ideas?
谁有想法？
采纳答案by Brian
I suggest you quickly learn SQL queries :)
我建议你快速学习 SQL 查询 :)
SELECT * from accountinfo where username = 'something'
回答by MD Sayem Ahmed
SELECT count(*) AS num_user
FROM accountinfo
WHERE username = "your_user_name"
which will give you a non-zero value if your_user_namealready exists in the database. If it doesn't exist, then you will get zero.
如果your_user_name数据库中已经存在，它将为您提供一个非零值。如果它不存在，那么你将得到零。
P.S.
聚苯乙烯
If you don't want duplicate username in the database, then you better add uniqueness constraints in your table.
如果您不想在数据库中出现重复的用户名，那么最好在表中添加唯一性约束。
To add uniqueness constraints, use this query -
要添加唯一性约束，请使用此查询 -
ALTER TABLE accountinfo ADD CONSTRAINTS unique_username UNIQUE (username);
Adding this uniqueness constraint will save you from a lot of troubles.
添加此唯一性约束将使您免于很多麻烦。
回答by feeela
Just query for the username:
只需查询用户名：
SELECT `username` FROM `accountinfo` WHERE `username` = :existing_username
-- or
SELECT `username` FROM `accountinfo` WHERE `username` LIKE :existing_username
