class ActiveRecord::ConnectionAdapters::PostgreSQLAdapter

def column_definitions(table_name)

Experimental RBS support (using type sampling data from the type_fusion project). 

def column_definitions: (String table_name) -> untyped

This signature was generated using 1 sample from 1 application.

- ::regclass is a function that gives the id for a table name
- format_type includes the column size constraint, e.g. varchar(50)
Query implementation notes:

take the first match from the schema search path.
If the table name is not prefixed with a schema, the database will

ORDER BY column.num
AND NOT column.is_dropped
AND column.num > 0
WHERE column.table_id = get_table_id('table_name')
AND column.num = default.column_num
ON column.table_id = default.table_id
FROM column LEFT JOIN default
SELECT column.name, column.type, default.value, column.comment
The underlying query is roughly:

Returns the list of a table's column names, data types, and default values. 
def column_definitions(table_name)
  query(<<~SQL, "SCHEMA")
      SELECT a.attname, format_type(a.atttypid, a.atttypmod),
             pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod,
             c.collname, col_description(a.attrelid, a.attnum) AS comment,
             #{supports_virtual_columns? ? 'attgenerated' : quote('')} as attgenerated
        FROM pg_attribute a
        LEFT JOIN pg_attrdef d ON a.attrelid = d.adrelid AND a.attnum = d.adnum
        LEFT JOIN pg_type t ON a.atttypid = t.oid
        LEFT JOIN pg_collation c ON a.attcollation = c.oid AND a.attcollation <> t.typcollation
       WHERE a.attrelid = #{quote(quote_table_name(table_name))}::regclass
         AND a.attnum > 0 AND NOT a.attisdropped
       ORDER BY a.attnum
  SQL
end