Drupal 7 Module Development

Database Access
Update queries
Update queries look like a hybrid of Insert and Select statements. They consist
of both fields to set on a table and conditions to restrict the query.
db_update('imports')
->condition('name', 'Chico')
->fields(array('address' => 'Go West St.'))
->execute();
The condition() method works exactly like the condition() method of Select
queries, and we can add multiple if we need to. fields() takes an associative array
of values to set. The above query is therefore equivalent to:
UPDATE {imports} SET address = 'Go West St.' WHERE name = 'Chico';
We still always want to use the dynamic approach rather than just call db_query(),
because on some databases (such as PostgreSQL or Oracle) there are cases where
the above query would not work and we would need to run multiple queries with
bound values and other odd edge cases. All of that handling is handled for us
automatically by the database layer.
The return value from execute() for Update queries is the number of records that
were changed by the query. Note that 'changed' does not mean 'matched'. If the
WHERE portion of the query matches a record but if that record already has the values
that it would be set to, it will not be changed and would not count towards the
return value from execute().
Delete queries
Delete queries should come as no surprise, as they consist of essentially just a
WHERE clause:
db_delete('imports')
->condition('name' => 'Zeppo')
->execute();
The return value from execute() for Delete query is the number of records that
were deleted by the query.
Merge queries
Merge queries are one of the oft-forgotten parts of SQL. In part, that's because the
most popular open source databases do not support them directly even though
they are part of the SQL specification.
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