SELECT

Select

Possible structures:

• columns
• sub querry
• SQL operator
• Array with combination of possible structures.

# String
constructor.select "name, email"
# Symbol
constructor.select :birthdate
# Array as columns
constructor.select [:phone, 'role']
# Array as SQL function
constructor.select [:_nullif, :row, :value]
# Hash with column alias(`AS`) as key and any available for `select` value
constructor.select _missed_calls_count:
                     { select: [:_count, [:_nullif, :connected, :true]],
                       from: [:calls, :c],
                       where: ['c.client_id = u.id',
                               ['direction = ?', 0]]}
# Hash with table alias as key and any available for `select` values
constructor.select m: [:common_rating, :work_rating, { _master_id: :id }]
# You can take a look of resulted data structure. In future, perhaps, Constructor will be more complicated and it will merge hashes...
constructor.structure
# => { select: ['name, email', :birthdate, :phone, 'role',
#               [:_nullif, :row, :value],
#               { _missed_calls_count: { select: [:_count, [:_nullif, :connected, :true]],
#                                        from: [:calls, :c],
#                                        where: ['c.client_id = u.id',
#                                                ['direction = ?', 0]]} }] },
#               { m: [:common_rating, :work_rating, { _master_id: :id }] }

constructor.build_sql
# => ['SELECT name, email, birthdate, phone, role, NULLIF(row, value), m.common_rating, m.work_rating, m.id AS master_id,
#             (SELECT COUNT(NULLIF(connected, TRUE))
#              FROM calls c
#              WHERE c.client_id = u.id AND direction = $1) AS missed_calls_count',
#     0]

Distinct Select

To specify distinct select you should add to your data structure :distinct value:

• true
• columns
  Or with Constructor instance methods:
• .distinct
  • distinct structure - optional
• .distinct_select
  • select structure
  • distinct structure - optional In constructor methods distinct: true passed by default

# as data
distinct: true, select: true
# => 'SELECT DISTINCT * '
# OR via constructor
constructor.distinct_select([:id, :name]).build_sql # => 'SELECT DISTINCT id, name'
# OR
constructor.distinct_select([:id, :name], :phone).build_sql # => 'SELECT DISTINCT ON(phone) id, name '