Alter table command
ALTER TABLE is an SQL data-definition statement that modifies the structure or properties of an existing table.
Learn SQL in a Month of Lunches
ALTER TABLE is an SQL statement that changes the structure or definition of an existing database table.
- How it is used
- Changes existing table structures, columns, keys, and constraints without using INSERT to create new rows.
- How deep it goes
- Demonstrates adding, validating, relating, and removing columns and constraints, while deferring broader product-specific syntax.
- Examples
- Uses title and category tables, CategoryID, named keys, populated rows, and DROP statements for constraints and columns.
- What you can do after
- Apply it via SQL to add or remove table elements and enforce relationships after checking existing data.
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Just Use Postgres!
The ALTER TABLE command is an SQL statement that changes the definition of an existing table, including its constraints.
- How it is used
- Strengthens database-level data integrity after table creation by adding or tightening constraints.
- How deep it goes
- Demonstrates adding checks and NOT NULL requirements, including existing-row failures, but does not detail broader table alterations.
- Examples
- Uses catalog price validation, a rejected negative-price update, and review NOT NULL and ranking constraints.
- What you can do after
- Operate/configure it to enforce new table constraints and diagnose failures caused by violating existing or incoming rows.
Related concepts
- SQLkind of · SQL is a standardized declarative language for defining, querying, and manipulating data in relational database systems.
- imperative programmingused by · Imperative programming is a programming paradigm that expresses computation as an ordered sequence of instructions specifying operations, control flow, or changes to state.
- database tableconfigures · A database table is a relational database structure that organizes records into rows and defined columns.
- constraintuses · A constraint is a condition or rule that restricts the permissible states, values, actions, or solutions in a system or problem.
- check constraintuses · A CHECK constraint is a database rule requiring each inserted or updated row or constrained value to satisfy a specified Boolean condition.
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