hook_schema structure - fill-in

API to handle database schemas.

A Drupal schema definition is an   structure representing one or more tables and their related keys and indexes. A schema is defined by hook_   (), which usually lives in a modulename.   file.

By implementing   () and specifying the tables your module declares, you can easily create and drop these tables on all supported database engines. You don't have to deal with the different SQL dialects for   creation and alteration of the supported database engines.

hook_schema() should return an array with a key for each   that the module defines.

The following keys are defined:

•     - A string in non-markup plain text describing this table and its purpose. References to other tables should be enclosed in curly-brackets. For example, the node_revisions table description field might contain "Stores per-revision title and body data for each {node}."
•    -  An associative array ('fieldname' => specification) that describes the table's database columns. The specification is also an array. The following specification parameters are defined:
• •    - A string in non-markup plain text describing this field and its purpose. References to other tables should be enclosed in curly-brackets. For example, the node table vid field description might contain "Always holds the largest (most recent) {node_revision}.vid value for this nid."
  •    - The generic datatype: 'char', 'varchar', 'text', 'blob', 'int', 'float', 'numeric', or 'serial'. Most types just map to the according database engine specific datatypes. Use 'serial' for auto incrementing fields. This will expand to 'INT auto_increment' on MySQL.
  •     ('pgsql_type', 'sqlite_type') etc. - If you need to use a record type not included in the officially supported list of types above, you can specify a type for each database backend. In this case, you can leave out the type parameter, but be advised that your schema will fail to load on backends that do not have a type specified. A possible solution can be to use the "text" type as a fallback.
  •   - A boolean indicating whether the field will be stored as a serialized string.
  •   - The data size: 'tiny', 'small', 'medium', 'normal', 'big'. This is a hint about the largest value the field will store and determines which of the database engine specific datatypes will be used (e.g. on MySQL, TINYINT vs. INT vs. BIGINT). 'normal', the default, selects the base type (e.g. on MySQL, INT, VARCHAR, BLOB, etc.). Not all sizes are available for all data types. See DatabaseSchema::getFieldTypeMap() for possible combinations.
  •    - If true, no NULL values will be allowed in this database column. Defaults to false.
  •   - The field's default value. The PHP type of the value matters: '', '0', and 0 are all different. If you specify '0' as the default value for a type 'int' field it will not work because '0' is a string containing the character "zero", not an integer.
  •   - The maximal length of a type 'char', 'varchar' or 'text' field. Ignored for other field types.
  •   - A boolean indicating whether a type 'int', 'float' and 'numeric' only is signed or unsigned. Defaults to FALSE. Ignored for other field types.
  •   ,   - For type 'numeric' fields, indicates the precision (total number of significant digits) and scale (decimal digits right of the decimal point). Both values are mandatory. Ignored for other field types.
  •   - A boolean indicating that MySQL should force 'char', 'varchar' or 'text' fields to use case-sensitive binary collation. This has no effect on other database types for which case sensitivity is already the default behavior.

All parameters apart from '   ' are optional except that type 'numeric' columns must specify '   ' and '   ', and type 'varchar' must specify the '   ' parameter.

•    - An array of one or more key column specifiers (see below) that form the primary key.
•    - An associative array of unique keys ('keyname' => specification). Each specification is an array of one or more key column specifiers (see below) that form a unique key on the table.
•    - An associative array of relations ('my_relation' => specification). Each specification is an array containing the name of the referenced table ('table'), and an array of column mappings ('columns'). Column mappings are defined by key pairs ('source_column' => 'referenced_column').
•    - An associative array of indexes ('indexname' => specification). Each specification is an array of one or more key column specifiers (see below) that form an index on the table.

A key column specifier is either a string naming a column or an array of two elements, column name and length, specifying a prefix of the named column.

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Source: http://api.drupal.org/api/drupal/includes%21database%21schema.inc/group/schemaapi/7