4. Reflection: what the catalog will answer

Shows exactly where the metadata boundary sits, because this is the thing most likely to decide whether your tool works. Metadata is split: the information_schema views are answered, and every SHOW form is refused. A tool that reflects through the first half gets somewhere; one that reflects through the second does not.

Five views, served by the same shared catalog the other wire protocols read: tables, columns, table_constraints, key_column_usage, referential_constraints.

-- List the tables in a schema.
SELECT table_name
  FROM information_schema.tables
 WHERE table_schema = 'shop';

-- Describe one table's columns.
SELECT column_name, data_type, is_nullable
  FROM information_schema.columns
 WHERE table_schema = 'shop' AND table_name = 'orders';

-- Constraints, and the columns they cover.
SELECT constraint_name, constraint_type FROM information_schema.table_constraints
 WHERE table_name = 'orders';
SELECT constraint_name, column_name FROM information_schema.key_column_usage
 WHERE table_name = 'orders';

SHOW TABLES;                      -- refused
SHOW DATABASES;                   -- refused
SHOW COLUMNS FROM orders;         -- refused
SHOW CREATE TABLE orders;         -- refused
SHOW INDEX FROM orders;           -- refused
SHOW WARNINGS;                    -- refused
SHOW VARIABLES LIKE 'sql_mode';   -- refused

The refusal is deliberate, and it is the safer of the two options. The shared front door carries a compatibility shim for a different protocol that answers any SHOW x with a single fabricated row reading x = 'on'. Left alone, SHOW TABLES would return that row: a confident, wrong answer. Refusing at the dialect boundary turns it into an error you can see.

// Safe: you tell the ORM the shape, it never asks the database.
const Order = sequelize.define(
  "Order",
  {
    id: { type: DataTypes.STRING, primaryKey: true },
    customer: DataTypes.STRING,
    total_cents: DataTypes.INTEGER,
    status: DataTypes.STRING,
  },
  { tableName: "orders", timestamps: false, freezeTableName: true },
);

// Not safe on this listener - each of these introspects with SHOW:
//   await sequelize.sync();
//   await sequelize.getQueryInterface().describeTable("orders");
//   await sequelize.getQueryInterface().showIndex("orders");

// Also not available: associations. Model the join in your query instead of
// asking the ORM to follow a relation for you.
//   Order.belongsTo(Customer);   // will not load

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