我创建了一个名为的表别名tbl
,我想从中选择。但我无法做到这一点。我知道我的代码不正确也不优化,但我只是测试 MySQLCASE
.
select
case
when exists (select username from tbl) then 'Username Exists'
else 'Username does not exist'
end
from (select 1 as id, 'bob' as username, 'pass' as password) as tbl
我收到错误:Table 'users.tbl' doesn't exist in database users
.
你有这个错误是因为查询中没有涉及物理表,因为tbl
只是您创建的别名。
如果您只想测试您的用户名是否存在,请执行以下查询:
SELECT CASE
WHEN id = 1 THEN 'Username Exists' ELSE 'Username does not exist'
END
FROM (SELECT 1 AS id, 'bob' AS username, 'pass' AS password) AS tbl
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