MaxCompute:Tables

Background information

Prepare the runtime environment

Basic operations

Operations on tables in a project

• Query all tables in a project.

  You can use the o.list_tables() method to query all tables in a project.

  for table in o.list_tables():
      print(table)

  You can specify the prefix parameter to query tables with a specified prefix.

  for table in o.list_tables(prefix="table_prefix"):
      print(table.name)

  This method displays only table names. Other table properties, such as table_schema and creation_time are not displayed. If you want to obtain these table properties, additional requests are required, and a longer time is consumed. In PyODPS 0.11.5 and later, you can add the extended=True configuration to the list_tables method to obtain the additional table properties.

  for table in o.list_tables(extended=True):
      print(table.name, table.creation_time)

  If you want to query tables by type, specify the type parameter. Examples:

  managed_tables=list (o.list_tables(type="managed_table"))  # Query internal tables.
  external_tables=list (o.list_tables(type="external_table"))  # Query external tables.
  virtual_views=list (o.list_tables(type="virtual_view"))  # Query views.
  materialized_views=list (o.list_tables(type="materialized_view"))  # Query materialized views.

• Check whether a table exists

  You can use the o.exist_table() method to check whether a table exists.

  print(o.exist_table('pyodps_iris'))
  # If True is returned, the table pyodps_iris exists.

• Obtain information about a table.

  Obtain information about a table by calling the o.get_table() method of a MaxCompute entry object.

  • Obtain the schema information of a table.

    t = o.get_table('pyodps_iris')
    print(t.schema) # Obtain the schema information of the table pyodps_iris.

    Sample response:

    odps.Schema {
      sepallength           : double      # Sepal length (cm)
      sepalwidth            : double      # Sepal width (cm)
      petallength           : double      # Petal length (cm)
      petalwidth            : double      # Petal width (cm)
      name                  : string      # Type
    }

  • Query the details about columns in a table.

    t = o.get_table('pyodps_iris')
    print(t.schema.columns) # Query the details about columns in the schema of the table pyodps_iris.

    Sample response:

    [<column sepallength, type double>,
     <column sepalwidth, type double>,
     <column petallength, type double>,
     <column petalwidth, type double>,
     <column name, type string>]

  • Query the details about a column in a table.

    t = o.get_table('pyodps_iris')
    print(t.schema['sepallength']) # Obtain the information about the sepallength column of the pyodps_iris table. 

    Sample response:

    <column sepallength, type double>

  • Obtain the comment of a column in a table.

    t = o.get_table('pyodps_iris')
    print(t.schema['sepallength'].comment) # Obtain the details about the column sepallength in the table pyodps_iris.

    Sample response:

    Sepal length (cm)

  • Obtain the lifecycle of a table.

    t = o.get_table('pyodps_iris')
    print(t.lifecycle) # Obtain the lifecycle of the table pyodps_iris.

    Sample response:

    -1

  • Obtain the time when a table was created.

    t = o.get_table('pyodps_iris')
    print(t.creation_time) # Obtain the time when the table pyodps_iris was created.

  • Check whether a table is a virtual view.

    t = o.get_table('pyodps_iris')
    print(t.is_virtual_view) # Check whether the table pyodps_iris is a virtual view. If False is returned, the table pyodps_iris is not a virtual view.

  Similar to the preceding examples, you can also use the t.size and t.comment methods to obtain the table size and table comment.

  Operations on tables across projects

  You can obtain information about a table from another project by specifying the project parameter.

  t = o.get_table('table_name', project='other_project')

  In the preceding code, set other_project to the name of the project from which you want to obtain information about a table, and set table_name to the name of the table whose information you want to obtain.

Create a table schema

Create a table

You can call the o.create_table() method to create a table by using a table schema or by specifying the names and data types of columns. When you create a table, you must make sure that the data types of columns in the table are valid.

Use a table schema to create a table

# Create a table schema.
from odps.models import Schema
schema = Schema.from_lists(['num', 'num2'], ['bigint', 'double'], ['pt'], ['string'])

# Create a table by using the schema that you created.
table = o.create_table('my_new_table', schema)

# Create a table only if no table with the same name exists. 
table = o.create_table('my_new_table', schema, if_not_exists=True)

# Configure the lifecycle of the table. 
table = o.create_table('my_new_table', schema, lifecycle=7)

You can call the print(o.exist_table('my_new_table')) method to check whether the table is successfully created. If True is returned, the table is successfully created.

Create a table by specifying the names and data types of the columns to be contained in the table

# Create a partitioned table named my_new_table with specified common columns and partition key columns. 
table = o.create_table('my_new_table', ('num bigint, num2 double', 'pt string'), if_not_exists=True)

# Create a non-partitioned table named my_new_table02. 
table = o.create_table('my_new_table02', 'num bigint, num2 double', if_not_exists=True)

You can call the print(o.exist_table('my_new_table')) method to check whether the table is successfully created. If True is returned, the table is successfully created.

Create a table by specifying the names and data types of the columns to be contained in the table: new data types in the MaxCompute V2.0 data type edition

from odps import options
options.sql.use_odps2_extension = True
table = o.create_table('my_new_table', 'cat smallint, content struct<title:varchar(100), body:string>')

Synchronize table updates

After another program updates a table, such as the table schema, you can call the reload() method to synchronize the update.

# Change the table schema.
from odps.models import Schema
schema = Schema.from_lists(['num', 'num2'], ['bigint', 'double'], ['pt'], ['string'])

# Call the reload() method to synchronize the update.
table = o.create_table('my_new_table', schema)
table.reload()

Write data to a table

• Call the write_table() method of a MaxCompute entry object to write data to a table.

  Important

  If a partitioned table does not contain the partition to which you want to write data, you can configure the create_partition parameter to create the partition.

  records = [[111, 1.0],                 # A list can be specified. 
            [222, 2.0],
            [333, 3.0],
            [444, 4.0]]
  o.write_table (my_new_table, records, partition='pt=test, create_partition=True) # Create a partition named test and write data to the partition.

  Note

  • Each time you call the write_table() method, MaxCompute generates a file on the server. This operation is time-consuming. In addition, if an excessive number of files are generated, the efficiency of subsequent queries is affected. We recommend that you write multiple records at a time or provide a generator object if you use the write_table() method.

  • If you call the write_table() method to write data to a table, new data will be appended to existing data. PyODPS does not provide options to overwrite existing data. You must manually delete the data that you want to overwrite. For a non-partitioned table, you must call the table.truncate() method to delete data. For a partitioned table, you must delete partitions and then create partitions again.

• Call the open_writer() method to write data to a table.

  t = o.get_table('my_new_table')
  with t.open_writer(partition='pt=test02', create_partition=True) as writer:  # Create a partition named test02 and write data to the partition.
      records = [[1, 1.0], # A list can be specified. 
                [2, 2.0],
                [3, 3.0],
                [4, 4.0]]
      writer.write(records)  # Records can be iterable objects.

  The following code shows how to write data to a multi-level partitioned table:

  t = o.get_table('test_table')
  with t.open_writer(partition='pt1=test1,pt2=test2') as writer:  # Write data in multi-level partitioning mode. 
      records = [t.new_record([111, 'aaa', True]),   # Record objects can be used. 
                 t.new_record([222, 'bbb', False]),
                 t.new_record([333, 'ccc', True]),
                 t.new_record([444, 'Chinese', False])]
      writer.write(records)

• Use multiple processes to concurrently write data to a table.

  If multiple processes concurrently write data to a table, all processes use the same session ID but write data to different blocks. Each block corresponds to a file on the server. After all the processes finish writing data, the main process submits the data.

  import random
  from multiprocessing import Pool
  from odps.tunnel import TableTunnel
  def write_records(tunnel, table, session_id, block_id):
      # Create a session with the specified session ID. 
      local_session = tunnel.create_upload_session(table.name, upload_id=session_id)
      # Create a writer with the specified block ID. 
      with local_session.open_record_writer(block_id) as writer:
          for i in range(5):
              # Generate data and write the data to the correct block. 
              record = table.new_record([random.randint(1, 100), random.random()])
              writer.write(record)
  
  if __name__ == '__main__':
      N_WORKERS = 3
  
      table = o.create_table('my_new_table', 'num bigint, num2 double', if_not_exists=True)
      tunnel = TableTunnel(o)
      upload_session = tunnel.create_upload_session(table.name)
  
      # All processes use the same session ID. 
      session_id = upload_session.id
  
      pool = Pool(processes=N_WORKERS)
      futures = []
      block_ids = []
      for i in range(N_WORKERS):
          futures.append(pool.apply_async(write_records, (tunnel, table, session_id, i)))
          block_ids.append(i)
      [f.get() for f in futures]
  
      # Submit the data in all the blocks. 
      upload_session.commit(block_ids)

Insert a record into a table

t = o.get_table('test_table')
r = t.new_record(['val0', 'val1'])  # The number of values must be equal to the number of fields in the table schema. 
r2 = t.new_record()     # You can leave the value empty. 
r2[0] = 'val0' # Configure a value based on an offset. 
r2['field1'] = 'val1'  # Configure a value based on the field name. 
r2.field1 = 'val1'  # Configure a value based on an attribute. 

print(record[0])  # Obtain the value at position 0. 
print(record['c_double_a'])  # Obtain a value based on a field. 
print(record.c_double_a)  # Obtain a value based on an attribute. 
print(record[0: 3])  # Perform slicing operations. 
print(record[0, 2, 3])  # Obtain values at multiple positions. 
print(record['c_int_a', 'c_double_a'])  # Obtain values based on multiple fields.

Obtain table data

Delete a table

o.delete_table('my_table_name', if_exists=True)  # Delete a table only if the table exists. 
t.drop() # Call the drop() method to drop a table if the table exists.

Convert a table into a DataFrame

PyODPS provides the DataFrame framework, which allows you to conveniently query and manage MaxCompute data. For more information, see DataFrame. You can call the to_df() method to convert a table into a DataFrame.

table = o.get_table('my_table_name')
df = table.to_df()

Manage table partitions

• Check whether a table is partitioned.

  table = o.get_table('my_new_table')
  if table.schema.partitions:
      print('Table %s is partitioned.' % table.name)

• Iterate over all the partitions in a table.

  table = o.get_table('my_new_table')
  for partition in table.partitions:  # Iterate over all partitions.
      print(partition.name)  # An iteration step. In this step, the partition name is displayed.
  for partition in table.iterate_partitions(spec='pt=test'):  # Iterate over level-2 partitions in the partition named test.
      print(partition.name)  # An iteration step. In this step, the partition name is displayed.
  for partition in table.iterate_partitions(spec='dt>20230119'):  # Iterate over level-2 partitions in the partitions that meet the dt>20230119 condition.
      print(partition.name)  # An iteration step. In this step, the partition name is displayed.

  Important

  In PyODPS 0.11.3 and later, you can specify logical expressions for iterate_partitions, such as dt>20230119 in the preceding example.

• Check whether a partition exists.

  table = o.get_table('my_new_table')
  table.exist_partition('pt=test,sub=2015')

• Obtain information about a partition.

  table = o.get_table('my_new_table')
  partition = table.get_partition('pt=test')
  print(partition.creation_time)
  partition.size

• Create a partition.

  t = o.get_table('my_new_table')
  t.create_partition('pt=test', if_not_exists=True)  # Create a partition only if no partition with the same name exists.

• Delete an existing partition.

  t = o.get_table('my_new_table')
  t.delete_partition('pt=test', if_exists=True)  # Set the if_exists parameter to True. This ensures that a partition is deleted only if the partition exists. 
  partition.drop()  # Call the drop() method to drop a partition if the partition exists.

Upload and download data by using MaxCompute Tunnel

MaxCompute Tunnel is the data tunnel of MaxCompute. You can use Tunnel to upload data to or download data from MaxCompute.

• Example of data upload

  from odps.tunnel import TableTunnel
  
  table = o.get_table('my_table')
  
  tunnel = TableTunnel(odps)
  upload_session = tunnel.create_upload_session(table.name, partition_spec='pt=test')
  
  with upload_session.open_record_writer(0) as writer:
      record = table.new_record()
      record[0] = 'test1'
      record[1] = 'id1'
      writer.write(record)
  
      record = table.new_record(['test2', 'id2'])
      writer.write(record)
  
  # You must execute the following statement outside the WITH code block. If you execute the following statement before data is written, an error is reported.
  upload_session.commit([0])

• Example of data download

  from odps.tunnel import TableTunnel
  
  tunnel = TableTunnel(odps)
  download_session = tunnel.create_download_session('my_table', partition_spec='pt=test')
  # Process each record. 
  with download_session.open_record_reader(0, download_session.count) as reader:
      for record in reader:
          print(record)  # An iteration step. In this step, the record is displayed.