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If you declare a table that has no `PRIMARY KEY` (and no `UNIQUE` constraints on `NOT NULL` columns) you're essentially allowing duplicate rows. Either the RDB
by cryptonector 2y ago
If you declare a table that has no `PRIMARY KEY` (and no `UNIQUE` constraints on `NOT NULL` columns) you're essentially allowing duplicate rows. Either the RDBMS treats such a table as having something of a primary key on all columns (but NULLs sneak duplicate rows back in!), or the RDBMS gives you a row ID like concept (ctid counts) to truly disambiguate duplicate rows.