关于Rails：Rails – 迁移错误 – PG :: InvalidSchemaName：错误：

Rails - Migration error - PG::InvalidSchemaName: ERROR:

当我运行rake db:migrate时，我收到以下错误：

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ActiveRecord::StatementInvalid: PG::InvalidSchemaName: ERROR: no schema has been selected to create in
: CREATE TABLE"schema_migrations" ("version" character varying NOT NULL)

PG::InvalidSchemaName: ERROR: no schema has been selected to create in

Tasks: TOP => db:migrate
(See full trace by running
ActiveRecord::StatementInvalid: PG::InvalidSchemaName: ERROR: no schema has been selected to create in
: CREATE TABLE"schema_migrations" ("version" character varying NOT NULL)

PG::InvalidSchemaName: ERROR: no schema has been selected to create in

Tasks: TOP => db:migrate
(See full trace by running task with --trace) task with --trace)

我不知道如何解决它，并欢迎任何想法。

我正在运行rails 4。

出现这个错误是因为我最初使用的是MySQL数据库(工作正常)，但后来切换到pgSQL以便轻松上传到heroku。现在它既不在本地主机也不在heroku上工作。