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  2. Primary key - Wikipedia

    en.wikipedia.org/wiki/Primary_key

    In the relational model of databases, a primary key is a designated attribute that can reliably identify and distinguish between each individual record in a table.The database creator can choose an existing unique attribute or combination of attributes from the table (a natural key) to act as its primary key, or create a new attribute containing a unique ID that exists solely for this purpose ...

  3. Database index - Wikipedia

    en.wikipedia.org/wiki/Database_index

    Database systems usually implicitly create an index on a set of columns declared PRIMARY KEY, and some are capable of using an already-existing index to police this constraint. Many database systems require that both referencing and referenced sets of columns in a FOREIGN KEY constraint are indexed, thus improving performance of inserts ...

  4. Insert (SQL) - Wikipedia

    en.wikipedia.org/wiki/Insert_(SQL)

    Using a SELECT statement after the INSERT statement with a database-specific function that returns the generated primary key for the most recently inserted row. For example, LAST_INSERT_ID() for MySQL. Using a unique combination of elements from the original SQL INSERT in a subsequent SELECT statement.

  5. Relational database - Wikipedia

    en.wikipedia.org/wiki/Relational_database

    The use of efficient indexes on both primary and foreign keys can dramatically improve query performance. This is because B-tree indexes result in query times proportional to log(n) where n is the number of rows in a table and hash indexes result in constant time queries (no size dependency as long as the relevant part of the index fits into ...

  6. SQL syntax - Wikipedia

    en.wikipedia.org/wiki/SQL_syntax

    SQL statements also include the semicolon (";") statement terminator. Though not required on every platform, it is defined as a standard part of the SQL grammar. Insignificant whitespace is generally ignored in SQL statements and queries, making it easier to format SQL code for readability.

  7. Surrogate key - Wikipedia

    en.wikipedia.org/wiki/Surrogate_key

    Some database designers use surrogate keys systematically regardless of the suitability of other candidate keys, while others will use a key already present in the data, if there is one. Some of the alternate names ("system-generated key") describe the way of generating new surrogate values rather than the nature of the surrogate concept.

  8. Database trigger - Wikipedia

    en.wikipedia.org/wiki/Database_trigger

    When creating a trigger to determine if it is statement or row level simply include the FOR EACH ROW clause for a row level, or omit the clause for a statement level. Be cautious of using additional INSERT/UPDATE/DELETE commands within your trigger, because trigger recursion is possible, causing unwanted behavior. In the examples below each ...

  9. Identity column - Wikipedia

    en.wikipedia.org/wiki/Identity_column

    An identity column differs from a primary key in that its values are managed by the server and usually cannot be modified. In many cases an identity column is used as a primary key; however, this is not always the case. It is a common misconception that an identity column will enforce uniqueness; however, this is not the case. If you want to ...