Database abstraction layer

Allow the use of different database servers using the same code base.

Drupal provides a slim database abstraction layer to provide developers with the ability to support multiple database servers easily. The intent of this layer is to preserve the syntax and power of SQL as much as possible, while letting Drupal control the pieces of queries that need to be written differently for different servers and provide basic security checks.

Most Drupal database queries are performed by a call to db_query() or db_query_range(). Module authors should also consider using pager_query() for queries that return results that need to be presented on multiple pages, and tablesort_sql() for generating appropriate queries for sortable tables.

For example, one might wish to return a list of the most recent 10 nodes authored by a given user. Instead of directly issuing the SQL query

  SELECT n.nid, n.title, n.created FROM node n WHERE n.uid = $uid LIMIT 0, 10;

one would instead call the Drupal functions:

$result = db_query_range('SELECT n.nid, n.title, n.created
    FROM {node} n WHERE n.uid = %d', $uid, 0, 10);
while ($node = db_fetch_object($result)) {

  // Perform operations on $node->body, etc. here.
}

Curly braces are used around "node" to provide table prefixing via db_prefix_tables(). The explicit use of a user ID is pulled out into an argument passed to db_query() so that SQL injection attacks from user input can be caught and nullified. The LIMIT syntax varies between database servers, so that is abstracted into db_query_range() arguments. Finally, note the common pattern of iterating over the result set using db_fetch_object().

File

includes/database.inc, line 15

Wrapper for database interface code.

Functions

Name	Location	Description
db_affected_rows	includes/database.mysql.inc	Determine the number of rows changed by the preceding query.
db_affected_rows	includes/database.mysqli.inc	Determine the number of rows changed by the preceding query.
db_affected_rows	includes/database.pgsql.inc	Determine the number of rows changed by the preceding query.
db_check_setup	includes/database.pgsql.inc	Verify if the database is set up correctly.
db_column_exists	includes/database.mysql.inc	Check if a column exists in the given table.
db_column_exists	includes/database.mysqli.inc	Check if a column exists in the given table.
db_column_exists	includes/database.pgsql.inc	Check if a column exists in the given table.
db_connect	includes/database.mysql.inc	Initialize a database connection.
db_connect	includes/database.mysqli.inc	Initialise a database connection.
db_connect	includes/database.pgsql.inc	Initialize a database connection.
db_decode_blob	includes/database.mysql.inc	Returns text from a Binary Large Object value.
db_decode_blob	includes/database.mysqli.inc	Returns text from a Binary Large OBject value.
db_decode_blob	includes/database.pgsql.inc	Returns text from a Binary Large OBject value. In case of PostgreSQL decodes data after select from bytea field.
db_distinct_field	includes/database.inc	Adds the DISTINCT flag to the supplied query and returns the altered query.
db_encode_blob	includes/database.mysql.inc	Returns a properly formatted Binary Large OBject value.
db_encode_blob	includes/database.mysqli.inc	Returns a properly formatted Binary Large Object value.
db_encode_blob	includes/database.pgsql.inc	Returns a properly formatted Binary Large OBject value. In case of PostgreSQL encodes data for insert into bytea field.
db_error	includes/database.mysql.inc	Determine whether the previous query caused an error.
db_error	includes/database.mysqli.inc	Determine whether the previous query caused an error.
db_error	includes/database.pgsql.inc	Determine whether the previous query caused an error.
db_escape_string	includes/database.mysql.inc	Prepare user input for use in a database query, preventing SQL injection attacks.
db_escape_string	includes/database.mysqli.inc	Prepare user input for use in a database query, preventing SQL injection attacks.
db_escape_string	includes/database.pgsql.inc	Prepare user input for use in a database query, preventing SQL injection attacks. Note: This function requires PostgreSQL 7.2 or later.
db_escape_table	includes/database.inc	Restrict a dynamic table, column or constraint name to safe characters.
db_fetch_array	includes/database.mysql.inc	Fetch one result row from the previous query as an array.
db_fetch_array	includes/database.mysqli.inc	Fetch one result row from the previous query as an array.
db_fetch_array	includes/database.pgsql.inc	Fetch one result row from the previous query as an array.
db_fetch_object	includes/database.mysql.inc	Fetch one result row from the previous query as an object.
db_fetch_object	includes/database.mysqli.inc	Fetch one result row from the previous query as an object.
db_fetch_object	includes/database.pgsql.inc	Fetch one result row from the previous query as an object.
db_is_active	includes/database.inc	Returns a boolean depending on the availability of the database.
db_last_insert_id	includes/database.pgsql.inc	Returns the last insert id. This function is thread safe.
db_lock_table	includes/database.mysql.inc	Lock a table.
db_lock_table	includes/database.mysqli.inc	Lock a table.
db_lock_table	includes/database.pgsql.inc	Lock a table. This function automatically starts a transaction.
db_placeholders	includes/database.inc	Generate placeholders for an array of query arguments of a single type.
db_prefix_tables	includes/database.inc	Append a database prefix to all tables in a query.
db_query	includes/database.pgsql.inc	Runs a basic query in the active database.
db_query_range	includes/database.mysql.inc	Runs a limited-range query in the active database.
db_query_range	includes/database.mysqli.inc	Runs a limited-range query in the active database.
db_query_range	includes/database.pgsql.inc	Runs a limited-range query in the active database.
db_query_temporary	includes/database.mysql.inc	Runs a SELECT query and stores its results in a temporary table.
db_query_temporary	includes/database.mysqli.inc	Runs a SELECT query and stores its results in a temporary table.
db_query_temporary	includes/database.pgsql.inc	Runs a SELECT query and stores its results in a temporary table.
db_result	includes/database.mysql.inc	Return an individual result field from the previous query.
db_result	includes/database.mysqli.inc	Return an individual result field from the previous query.
db_result	includes/database.pgsql.inc	Return an individual result field from the previous query.
db_rewrite_sql	includes/database.inc	Rewrites node, taxonomy and comment queries. Use it for listing queries. Do not use FROM table1, table2 syntax, use JOIN instead.
db_set_active	includes/database.inc	Activate a database for future queries.
db_status_report	includes/database.mysql.inc	Report database status.
db_status_report	includes/database.mysqli.inc	Report database status.
db_status_report	includes/database.pgsql.inc	Report database status.
db_table_exists	includes/database.mysql.inc	Check if a table exists.
db_table_exists	includes/database.mysqli.inc	Check if a table exists.
db_table_exists	includes/database.pgsql.inc	Check if a table exists.
db_unlock_tables	includes/database.mysql.inc	Unlock all locked tables.
db_unlock_tables	includes/database.mysqli.inc	Unlock all locked tables.
db_unlock_tables	includes/database.pgsql.inc	Unlock all locked tables. This function automatically commits a transaction.
db_version	includes/database.mysql.inc	Returns the version of the database server currently in use.
db_version	includes/database.mysqli.inc	Returns the version of the database server currently in use.
db_version	includes/database.pgsql.inc	Returns the version of the database server currently in use.
pager_query	includes/pager.inc	Perform a paged database query.
tablesort_sql	includes/tablesort.inc	Create an SQL sort clause.
update_sql	includes/database.inc	Perform an SQL query and return success or failure.
_db_error_page	includes/database.inc	Helper function to show fatal database errors.
_db_query	includes/database.mysql.inc	Helper function for db_query().
_db_query	includes/database.mysqli.inc	Helper function for db_query().
_db_query	includes/database.pgsql.inc	Helper function for db_query().
_db_query_callback	includes/database.inc	Helper function for db_query().
_db_rewrite_sql	includes/database.inc	Helper function for db_rewrite_sql.

Constants

Name	Location	Description
DB_QUERY_REGEXP	includes/database.inc	Indicates the place holders that should be replaced in _db_query_callback().