PostgreSQL incompatibilities: double-quotes quote columns in PostgreSQL

Alchemy is generating PostgreSQL errors on Drupal sites running PostgreSQL. The problem is that some queries are using double quotes(") to quote strings within the query. In PostgreSQL, double quotes are used to quote columns (e.g. in cases where a column name is the same as a reserved word), and only single quotes(') are used to quote strings. Best practice is to use double quotes to delimit the string containing a SQL query, and single quotes to delimit actual strings within the query. E.g., do

$sql = "DELETE FROM {alchemy_cache} WHERE nid = %d AND command = '%s' ";

not

$sql = 'DELETE FROM {alchemy_cache} WHERE nid = %d AND command = "%s'" ';

This will be compatible with both MySQL and PostgreSQL.

Patches to follow in the comment.