Which term is used to denote the column in a database table that uniquely identifies each row?

Which term is used to denote the column in a database table that uniquely identifies each row?

• A. Primary key
• B. Foreign key
• C. Index
• D. Field

Answer: (A)

The main idea is how a table can distinguish every row uniquely. The column that does this is the primary key. It must hold unique values for each row and cannot be left empty, so no two rows share the same key and every row has one. It can be a single column or a combination of columns (a composite key), but its role is to serve as the official identifier for that table and is often used to link to other tables via foreign keys. A foreign key, by contrast, points to a primary key in another table to establish relationships, not to identify rows within its own table. An index speeds up lookups on one or more columns and may be unique, but its main job is performance, not guaranteeing a unique row identity across the table. A field is simply any column in a table, not necessarily unique. So, the column that uniquely identifies each row is the primary key.

The main idea is how a table can distinguish every row uniquely. The column that does this is the primary key. It must hold unique values for each row and cannot be left empty, so no two rows share the same key and every row has one. It can be a single column or a combination of columns (a composite key), but its role is to serve as the official identifier for that table and is often used to link to other tables via foreign keys.

A foreign key, by contrast, points to a primary key in another table to establish relationships, not to identify rows within its own table.

An index speeds up lookups on one or more columns and may be unique, but its main job is performance, not guaranteeing a unique row identity across the table.

A field is simply any column in a table, not necessarily unique.

So, the column that uniquely identifies each row is the primary key.