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  2. ISO/IEC 9075 - Wikipedia

    en.wikipedia.org/wiki/ISO/IEC_9075

    ISO/IEC 9075 "Information technology - Database languages - SQL" is an international standard for Structured Query Language, and is considered as specifying the minimum for what a database engine should fulfill in terms of SQL syntax, which is called Core SQL. The standard also defines a number of optional features.

  3. SQL syntax - Wikipedia

    en.wikipedia.org/wiki/SQL_syntax

    Each column in an SQL table declares the type(s) that column may contain. ANSI SQL includes the following data types. [14] Character strings and national character strings. CHARACTER(n) (or CHAR(n)): fixed-width n-character string, padded with spaces as needed; CHARACTER VARYING(n) (or VARCHAR(n)): variable-width string with a maximum size of n ...

  4. Database normalization - Wikipedia

    en.wikipedia.org/wiki/Database_normalization

    Recall that the Book table below has a composite key of {Title, Format}, which will not satisfy 2NF if some subset of that key is a determinant. At this point in our design the key is not finalized as the primary key , so it is called a candidate key .

  5. Entity integrity - Wikipedia

    en.wikipedia.org/wiki/Entity_integrity

    Entity integrity is concerned with ensuring that each row of a table has a unique and non-null primary key value; this is the same as saying that each row in a table represents a single instance of the entity type modelled by the table.

  6. SQL:2011 - Wikipedia

    en.wikipedia.org/wiki/SQL:2011

    SQL:2011 or ISO/IEC 9075:2011 (under the general title "Information technology – Database languages – SQL") is the seventh revision of the ISO (1987) and ANSI (1986) standard for the SQL database query language. It was formally adopted in December 2011. [1] The standard consists of 9 parts which are described in detail in SQL.

  7. Boyce–Codd normal form - Wikipedia

    en.wikipedia.org/wiki/Boyce–Codd_normal_form

    If a relational schema is in BCNF, then all redundancy based on functional dependency has been removed, [4] although other types of redundancy may still exist. A relational schema R is in Boyce–Codd normal form if and only if for every one of its functional dependencies X → Y, at least one of the following conditions hold: [5]

  8. Denormalization - Wikipedia

    en.wikipedia.org/wiki/Denormalization

    Denormalization is a strategy used on a previously-normalized database to increase performance. In computing, denormalization is the process of trying to improve the read performance of a database, at the expense of losing some write performance, by adding redundant copies of data or by grouping data.

  9. Fourth normal form - Wikipedia

    en.wikipedia.org/wiki/Fourth_normal_form

    Fourth normal form (4NF) is a normal form used in database normalization.Introduced by Ronald Fagin in 1977, 4NF is the next level of normalization after Boyce–Codd normal form (BCNF).