require "clickhouse"

client = Clickhouse.new(host: "localhost", port: 8123)

res = client.execute <<-SQL
  SELECT   database, count(*)
  FROM     system.tables
  GROUP BY database
  SQL

res.rows    # => 2
res.to_a    # => [["system", 35], ["test", 9], ...

res.map(String, UInt64).each do |(name, cnt)|
  p [name, cnt]

client.databases # => ["default", "system", ...

Clickhouse
  def self.new(host = "localhost", port = 8123, database = nil, ...)
  def execute(sql : String) : Response
  # reflection
  def databases : Array(Database)
  def database(name : String) : Database
  def tables(database : String) : Array(Table)
  def table(database : String, name : String) : Table

Clickhouse::Response
  def each
  def each_hash
  def records : Array(Record)
  def map(*types : *T) forall T
  def map(**types : **T) forall T
  def success? : Response?
  def success! : Response
  def to_json : String

Clickhouse::Database
  def name : String
  def tables : Array(Table)

Clickhouse::Table
  def name : String
  def columns : Array(Column)
  def count : UInt64

Clickhouse::Column
  def name : String
  def type : String

res.each do |ary|
  ary.class        # => Array(Clickhouse::Type)
  ary[0]           # => "system"
  ary[1]           # => 35

res.each_hash do |hash|
  hash.class       # => Hash(String, Clickhouse::Type))
  hash["database"] # => "system"
  hash["count(*)"] # => 35

res.records.each do |hash|
  hash.class       # => Hash(String, Clickhouse::Type))
  hash["database"] # => "system"
  hash["count(*)"] # => 35

res.map(String, UInt64).each do |(name, cnt)|
  name.class       # => String
  name             # => "system"
  cnt              # => 35

res.map(name: String, cnt: UInt64).each do |r|
  r.class          # => NamedTuple(name: String, cnt: UInt64)
  r["name"]        # => "system"
  r["cnt"]         # => 35

res.statistics.elapsed    # => 0.000671276
res.statistics.rows_read  # => 1
res.statistics.bytes_read # => 1

client = Clickhouse.new
client.databases.map(&.name)
# => ["default", "system", ...

system = client.database("system")
system.tables.map(&.name)
# => ["aggregate_function_combinators", "asynchronous_metrics", ...

table = client.table("system", "parts")
table.columns.map(&.name)
# => ["partition", "name", ...

table.columns.select(&.type.=~(/DateTime/)).map(&.name)
# => ["modification_time", "remove_time", "min_time", "max_time"]

buf = <<-SQL
  CREATE TABLE logs (
    `d` Date,
    `k` UInt64
  )
  ENGINE = MergeTree(d, k, 8192)
  SQL

create = Clickhouse::Schema::Create.parse(buf)
create.table            # => "logs"
create.column("d").type # => "Date"
create.engine           # => "MergeTree(d, k, 8192)"
create.to_sql           # should be `buf`

migrate = Migrate.new(columns1, columns2)
migrate.plans.size  # => 4
migrate.map(&.name) # => ["id", "age", "hobby"]

puts migrate.manifest
# 1  id     MODIFY COLUMN `id` Int64
# 2  name   # NOP
# 3  age    DROP COLUMN `age`
# 4  hobby  ADD COLUMN `hobby` String

string = %( foo from:user1 "a:b" -bar -"-x:-y" )
tokens = Clickhouse::QueryTokenizer.tokenize(string)

puts tokens.map(&.inspect)
# [Included("foo"), Modified("user1"), Exactly("a:b"), -Included("bar"), -Exactly("-x:-y")]
puts tokens.map(&.to_s)
 # ["foo", "from:user1", "\"a:b\"", "-bar", "-\"-x:-y\""]