Sequel is very flexibile when it comes to filtering records. You can specify your conditions as a custom string, as a string with parameters, as a hash of values to compare against, or as ruby code that Sequel translates into SQL expressions.
If you wish to write your SQL by hand, you can just supply it to the dataset’s #where method:
items.where('x < 10').sql #=> "SELECT * FROM items WHERE x < 10"
In order to prevent SQL injection, you can replace literal values with question marks and supply the values as additional arguments:
items.where('category = ?', 'ruby').sql #=> "SELECT * FROM items WHERE category = 'ruby'"
You can also use placeholders with :placeholder and a hash of placeholder values:
items.where('category = :category', :category=>'ruby').sql #=> "SELECT * FROM items WHERE category = 'ruby'"
Sequel also allows you to specify functions by using the Sequel.function method:
items.literal(Sequel.function(:avg, :price)) #=> "avg(price)"
If you are specifying a filter/selection/order, you can use a virtual row block:
items.select{avg(price)}
You can also use the core_extensions extension and the sql_function method:
:avg.sql_function(:price)
If you just need to compare records against values, you can supply a hash:
items.where(:category => 'ruby').sql #=> "SELECT * FROM items WHERE (category = 'ruby')"
Sequel can check for null values:
items.where(:category => nil).sql #=> "SELECT * FROM items WHERE (category IS NULL)"
Or compare two columns:
items.where(:x => :some_table__y).sql #=> "SELECT * FROM items WHERE (x = some_table.y)"
And also compare against multiple values:
items.where(:category => ['ruby', 'perl']).sql #=> "SELECT * FROM items WHERE (category IN ('ruby', 'perl'))"
Ranges (both inclusive and exclusive) can also be used:
items.where(:price => 100..200).sql #=> "SELECT * FROM items WHERE (price >= 100 AND price <= 200)" items.where(:price => 100...200).sql #=> "SELECT * FROM items WHERE (price >= 100 AND price < 200)"
If you need to select multiple items from a dataset, you can supply an array:
item_array = [1, 38, 47, 99] items.where(:id => item_array).sql #=> “SELECT * FROM items WHERE (id IN (1, 38, 47, 99))”
You can pass a block to where, which is evaluated in a special context:
items.where{price * 2 < 50}.sql #=> "SELECT * FROM items WHERE ((price * 2) < 50)
This works for the standard inequality and arithmetic operators:
items.where{price + 100 < 200}.sql #=> "SELECT * FROM items WHERE ((price + 100) < 200) items.where{price - 100 > 200}.sql #=> "SELECT * FROM items WHERE ((price - 100) > 200) items.where{price * 100 <= 200}.sql #=> "SELECT * FROM items WHERE ((price * 100) <= 200) items.where{price / 100 >= 200}.sql #=> "SELECT * FROM items WHERE ((price / 100) >= 200)
You use the overloaded bitwise and (&) and or (|) operators to combine expressions:
items.where{(price + 100 < 200) & (price * 100 <= 200)}.sql #=> "SELECT * FROM items WHERE (((price + 100) < 200) AND ((price * 100) <= 200)) items.where{(price - 100 > 200) | (price / 100 >= 200)}.sql #=> "SELECT * FROM items WHERE (((price - 100) > 200) OR ((price / 100) >= 200))
To filter by equality, you use the standard hash, which can be combined with other expressions using Sequel.& and Sequel.|:
items.where{Sequel.&({:category => 'ruby'}, (price + 100 < 200))}.sql #=> "SELECT * FROM items WHERE ((category = 'ruby') AND ((price + 100) < 200))"
This works with other hash values, such as arrays and ranges:
items.where{Sequel.|({:category => ['ruby', 'other']}, (:price - 100 > 200))}.sql
#=> "SELECT * FROM items WHERE ((category IN ('ruby', 'other')) OR ((price - 100) <= 200))"
items.where{Sequel.&({:price => (100..200)}, :active)).sql
#=> "SELECT * FROM items WHERE ((price >= 100 AND price <= 200) AND active)"
You can use the exclude method to exclude conditions:
items.exclude(:category => 'ruby').sql #=> "SELECT * FROM items WHERE (category != 'ruby')" items.exclude(:active).sql #=> "SELECT * FROM items WHERE NOT active" items.exclude{price / 100 >= 200}.sql #=> "SELECT * FROM items WHERE ((price / 100) < 200)
You can also compare against other columns:
items.where{credit > debit}.sql #=> "SELECT * FROM items WHERE (credit > debit)
Or against SQL functions:
items.where{price - 100 < max(price)}.sql #=> "SELECT * FROM items WHERE ((price - 100) < max(price))"
You can search SQL strings using the Sequel.like method:
items.where(Sequel.like(:name, 'Acme%')).sql #=> "SELECT * FROM items WHERE (name LIKE 'Acme%')"
You can specify a Regexp as a like argument, but this will probably only work on PostgreSQL and MySQL:
items.where(Sequel.like(:name, /Acme.*/)).sql #=> "SELECT * FROM items WHERE (name ~ 'Acme.*')"
Like can also take more than one argument:
items.where(Sequel.like(:name, 'Acme%', /Beta.*/)).sql #=> "SELECT * FROM items WHERE ((name LIKE 'Acme%') OR (name ~ 'Beta.*'))"
You can concatenate SQL strings using Sequel.join:
items.where(Sequel.join([:name, :comment]).like('%acme%')).sql #=> "SELECT * FROM items WHERE ((name || comment) LIKE 'Acme%')"
Array#sql_string_join also takes a join argument:
items.filter(Sequel.join([:name, :comment], ' ').like('%acme%')).sql #=> "SELECT * FROM items WHERE ((name || ' ' || comment) LIKE 'Acme%')"
One of the best features of Sequel is the ability to use datasets as sub-queries. Sub-queries can be very useful for filtering records, and many times provide a simpler alternative to table joins. Sub-queries can be used in all forms of filters:
refs = consumer_refs.where(:logged_in).select(:consumer_id) consumers.where(:id => refs).sql #=> "SELECT * FROM consumers WHERE (id IN (SELECT consumer_id FROM consumer_refs WHERE logged_in))"
Note that if you are checking for the inclusion of a single column in a subselect, the subselect should only select a single column.
By default, if you chain calls to where, the conditions get ANDed together. If you want to use an OR for a condition, you can use the or method:
items.where(:name=>'Food').or(:vendor=>1).sql #=> "SELECT * FROM items WHERE ((name = 'Food') OR (vendor = 1))"