Data Definition Language (DDL) and Data Manipulation Language (DML) flashcards

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What is Data Definition Language (DDL)?

A subset of SQL used to define and manage the database structure or schema. Its commands affect the tables themselves, not the data inside them.

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What is Data Manipulation Language (DML)?

A subset of SQL used to retrieve, insert, update, and delete data within the database tables.

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Which SQL command creates a new table?

CREATE TABLE. This is a DDL command.

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Which SQL command modifies the structure of an existing table?

ALTER TABLE. This DDL command can add, delete, or modify columns.

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Which SQL command completely removes a table and all its data?

DROP TABLE. This is a DDL command and is irreversible.

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Which SQL command retrieves data from a database?

SELECT. This is the primary DML command for querying data.

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Which SQL command adds a new row of data to a table?

INSERT INTO. This is a DML command.

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Which SQL command modifies existing data in a table?

UPDATE. This DML command must be used with a WHERE clause to specify which rows to change.

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Which SQL command removes one or more rows from a table?

DELETE FROM. This DML command should almost always be used with a WHERE clause to avoid deleting all rows.

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What is the difference between DELETE and DROP?

DELETE is a DML command that removes rows of data from a table. DROP is a DDL command that removes the entire table structure and all its data.

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What is a PRIMARY KEY constraint?

A DDL constraint that uniquely identifies each record in a table. It cannot contain NULL values and must be unique.

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What is a FOREIGN KEY constraint?

A DDL constraint used to link two tables together. It is a field in one table that refers to the PRIMARY KEY in another table, enforcing referential integrity.

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What is the purpose of the NOT NULL constraint?

A DDL constraint that ensures a column cannot have a NULL (empty) value. It forces a field to always contain a value.