#MySQL选择数据库

-- Select (use) a database

-- Example

-- Verify current database

-- Get current database name

-- Equivalent

-- Get current database character set

-- Get database size

-- List tables in current database

-- List tables with additional info

-- Use fully qualified table names

-- Join tables from different databases

-- Use specific database tables in queries

-- Query across databases

-- Aggregate across databases

-- Create temporary table in current database

-- Temporary table is visible only in current session
-- It uses the current database context

-- Switch database (temporary table still accessible)

-- Create procedure in specific database

-- Call procedure (uses database where it was created)

-- Prepare statement with dynamic database

-- Set database for session

-- Session persists until disconnected or changed
-- All queries use 'myapp' database

-- Switch database in same session

-- Current database changes for rest of session

-- User can access specific databases

-- User cannot access other databases

-- Good: Use explicit database names

-- Avoid: Rely on current database context

-- No database selected
-- Error: No database selected
-- Solution: USE database_name;

-- Unknown database
-- Error: Unknown database 'database_name'
-- Solution: Check database name with SHOW DATABASES

-- Access denied
-- Error: Access denied for user to database
-- Solution: Check user privileges

-- Check current database

-- List available databases

-- Check user privileges

-- Check table existence