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It uses the MySQL client library API as a data transport, treating remote tables as if they were located on the local server. Each Federated table that is defined there is one .frm (data definition file containing information such as the URL of the data source). The actual data can exist on a local or remote MySQL instance.
A table (called the referencing table) can refer to a column (or a group of columns) in another table (the referenced table) by using a foreign key. The referenced column(s) in the referenced table must be under a unique constraint, such as a primary key. Also, self-references are possible (not fully implemented in MS SQL Server though [5]).
Files format depends on the ROW_FORMAT table option. The following formats are available: FIXED: Fixed is a format where all data (including variable-length types) have a fixed length. This format is faster to read, and improves corrupted tables repair. If a table contains big variable-length columns (BLOB or TEXT) it cannot use the FIXED format.
It is possible to convert integer and float columns back to PHP numbers by setting the MYSQLI_OPT_INT_AND_FLOAT_NATIVE connection option, if using the mysqlnd library. If set, the mysqlnd library will check the result set meta data column types and convert numeric SQL columns to PHP numbers, if the PHP data type value range allows for it.
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 ...
Reserved words in SQL and related products In SQL:2023 [3] In IBM Db2 13 [4] In Mimer SQL 11.0 [5] In MySQL 8.0 [6] In Oracle Database 23c [7] In PostgreSQL 16 [1] In Microsoft SQL Server 2022 [2]
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
All columns are regular [i.e. rows have no hidden components such as row IDs, object IDs, or hidden timestamps]. Violation of any of these conditions would mean that the table is not strictly relational, and therefore that it is not in first normal form. Examples of tables (or views) that would not meet this definition of first normal form are: