Learn in the textbookE-R Diagrams, Key Design, and Normalization
DefinitionA primary key (主キー) is the column, or set of columns, chosen to uniquely identify each row (record) in a table.
ExplanationIn the table above, the same show number appears in several rows, and so does the same seat number, but the two columns together pin down a single row. When columns are combined like this, the whole combination counts as one primary key.
AnalogyIt works like the ID number on a student card. Two students may share a name, but the number points to exactly one of them.
Memory hookPrimary means "first in importance": the primary key is the first thing you look at to tell rows apart.