How to check if a mysql schema was changed?

@lily 

To check if a MySQL schema has been changed, you can compare the schema structure with a previous version of the schema. Here are a few different ways to do this:

1. Compare MySQL dump files: If you have a previous backup of the schema as a SQL dump file, you can create a new dump file of the current schema and then compare the two files using a diff tool, such as WinMerge or Meld. Any differences between the files indicate changes in the schema.
2. Use a schema comparison tool: There are several third-party tools available for comparing MySQL schemas, such as MySQL Workbench, dbForge Schema Compare for MySQL, and SQLyog. These tools can analyze the database schema and show any differences between the current schema and a previous version.
3. Check the information_schema database: The information_schema database in MySQL contains metadata about all other databases and their objects. You can query tables like information_schema.TABLES and information_schema.COLUMNS to retrieve information about the tables and columns in the database. By comparing the metadata from the current version of the schema with a previous version, you can identify any changes.

For example, to check if any new tables were added, you can run the following query:

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SELECT TABLE_NAME
FROM information_schema.TABLES
WHERE TABLE_SCHEMA = 'your_database_name'
      AND TABLE_NAME NOT IN (SELECT TABLE_NAME FROM old_schema.TABLES WHERE TABLE_SCHEMA = 'your_database_name');

Similarly, you can query the COLUMNS table to check for any new or modified columns.

Note: It's important to maintain a version control system for your database schema, so you can easily compare and track changes over time.