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Documentation: reference/reference_lua/box_schema_sequence/create_index

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	specifying a sequence in create_index()
	You can use the :samp:`sequence={sequence-name}` (or :samp:`sequence={sequence-id}` or :samp:`sequence=true`) option when :ref:`creating <box_space-create_index>` or :doc:`altering </reference/reference_lua/box_index/alter>` a primary-key index. The sequence becomes associated with the index, so that the next ``insert()`` will put the next generated number into the primary-key field, if the field would otherwise be nil.
	The syntax may be any of: \|br\| :samp:`sequence = {sequence identifier}` \|br\| or :code:`sequence = {id =` :samp:`{sequence identifier}` :code:`}` \|br\| or :code:`sequence = {field =` :samp:`{field number}` :code:`}` \|br\| or :code:`sequence = {id =` :samp:`{sequence identifier}` :code:`, field =` :samp:`{field number}` :code:`}` \|br\| or :code:`sequence = true` \|br\| or :code:`sequence = {}`. \|br\| The sequence identifier may be either a number (the sequence id) or a string (the sequence name). The field number may be the ordinal number of any field in the index; default = 1. Examples of all possibilities: ``sequence = 1`` or ``sequence = 'sequence_name'`` or ``sequence = {id = 1}`` or ``sequence = {id = 'sequence_name'}`` or ``sequence = {id = 1, field = 1}`` or ``sequence = {id = 'sequence_name', field = 1}`` or ``sequence = {field = 1}`` or ``sequence = true`` or ``sequence = {}``. Notice that the sequence identifier can be omitted, if it is omitted then a new sequence is created automatically with default name = :samp:`{space-name}_seq`. Notice that the field number does not have to be 1, that is, the sequence can be associated with any field in the primary-key index.
	For example, if 'Q' is a sequence and 'T' is a new space, then this will work:
	tarantool> box.space.T:create_index('Q',{sequence='Q'}) --- - unique: true parts: - type: unsigned is_nullable: false fieldno: 1 sequence_id: 8 id: 0 space_id: 514 name: Q type: TREE ...
	(Notice that the index now has a ``sequence_id`` field.)
	And this will work:
	tarantool> box.space.T:insert{box.NULL,0} --- - [1, 0] ...
	The index key type may be either 'integer' or 'unsigned'. If any of the sequence options is a negative number, then the index key type should be 'integer'.
	Users should not insert a value greater than 9223372036854775807, which is 2^63 - 1, in the indexed field. The sequence generator will ignore it.
	A sequence cannot be dropped if it is associated with an index. However, :ref:`index_object:alter() <box_index-alter>` can be used to say that a sequence is not associated with an index, for example ``box.space.T.index.I:alter({sequence=false})``.
	If a sequence was created automatically because the sequence identifier was omitted, then it will be dropped automatically if the index is altered so that ``sequence=false``, or if the index is dropped.
	``index_object:alter()`` can also be used to associate a sequence with an existing index, with the same syntax for options.
	When a sequence is used with an index based on a JSON path, inserted tuples must have all components of the path preceding the autoincrement field, and the autoincrement field. To achieve that use ``box.NULL`` rather than ``nil``. Example:
	s = box.schema.space.create('test') s:create_index('pk', {parts = {{'[1].a.b[1]', 'unsigned'}}, sequence = true}) s:replace{} -- error s:replace{{c = {}}} -- error s:replace{{a = {c = {}}}} -- error s:replace{{a = {b = {}}}} -- error s:replace{{a = {b = {nil}}}} -- error s:replace{{a = {b = {box.NULL}}}} -- ok

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