Sql Ddl — Free Sql Tutorial

TL;DR: Learn Sql Ddl in Sql with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Sql Ddl in Sql

DDL (Data Definition Language) is the SQL commands that define the structure of a database: CREATE TABLE, ALTER TABLE, DROP TABLE. Understanding DDL is essential for designing databases from scratch.

Constraints: Rules that enforce data integrity. PRIMARY KEY: uniquely identifies each row, cannot be NULL or duplicate. NOT NULL: column must always have a value. UNIQUE: no duplicates allowed (but can be NULL). DEFAULT: value used if none is specified. CHECK: value must meet a condition. FOREIGN KEY: links to another table's primary key.

Good database design uses constraints to prevent bad data from entering the database — better to reject bad input at the database level than to deal with corrupted data later.

CREATE TABLE table_name (
  column1 datatype CONSTRAINT,
  column2 datatype CONSTRAINT,
  PRIMARY KEY (column1),
  FOREIGN KEY (column2) REFERENCES other_table(pk)
);

-- Data types: INT, VARCHAR(n), DECIMAL(p,s),
-- DATE, BOOLEAN, TEXT

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