query
¶
query(
table_name: TableArn,
*,
config_overrides: Optional[DynamoDBClientConfig] = None,
index_name: Optional[IndexName] = None,
select: Optional[Select] = None,
attributes_to_get: Optional[AttributeNameList] = None,
limit: Optional[PositiveIntegerObject] = None,
consistent_read: Optional[ConsistentRead] = None,
key_conditions: Optional[KeyConditions] = None,
query_filter: Optional[FilterConditionMap] = None,
conditional_operator: Optional[ConditionalOperator] = None,
scan_index_forward: Optional[BooleanObject] = None,
exclusive_start_key: Optional[Key] = None,
return_consumed_capacity: Optional[ReturnConsumedCapacity] = None,
projection_expression: Optional[ProjectionExpression] = None,
filter_expression: Optional[ConditionExpression] = None,
key_condition_expression: Optional[KeyExpression] = None,
expression_attribute_names: Optional[ExpressionAttributeNameMap] = None,
expression_attribute_values: Optional[ExpressionAttributeValueMap] = None,
) -> QueryOutput
You must provide the name of the partition key attribute and a single value for that attribute. Query returns all items with that partition key value. Optionally, you can provide a sort key attribute and use a comparison operator to refine the search results.
Use the KeyConditionExpression parameter to provide a specific value for the partition key. The Query operation will return all of the items from the table or index with that partition key value. You can optionally narrow the scope of the Query operation by specifying a sort key value and a comparison operator in KeyConditionExpression. To further refine the Query results, you can optionally provide a FilterExpression. A FilterExpression determines which items within the results should be returned to you. All of the other results are discarded.
A Query operation always returns a result set. If no matching items are found, the result set will be empty. Queries that do not return results consume the minimum number of read capacity units for that type of read operation.
DynamoDB calculates the number of read capacity units consumed based on item size, not on the amount of data that is returned to an application. The number of capacity units consumed will be the same whether you request all of the attributes (the default behavior) or just some of them (using a projection expression). The number will also be the same whether or not you use a FilterExpression.
Query results are always sorted by the sort key value. If the data type of the sort key is Number, the results are returned in numeric order; otherwise, the results are returned in order of UTF-8 bytes. By default, the sort order is ascending. To reverse the order, set the ScanIndexForward parameter to false.
A single Query operation will read up to the maximum number of items set (if using the Limit parameter) or a maximum of 1 MB of data and then apply any filtering to the results using FilterExpression. If LastEvaluatedKey is present in the response, you will need to paginate the result set. For more information, see Paginating the Results in the Amazon DynamoDB Developer Guide.
FilterExpression is applied after a Query finishes, but before the results are returned. A FilterExpression cannot contain partition key or sort key attributes. You need to specify those attributes in the KeyConditionExpression.
A Query operation can return an empty result set and a LastEvaluatedKey if all the items read for the page of results are filtered out.
You can query a table, a local secondary index, or a global secondary index. For a query on a table or on a local secondary index, you can set the ConsistentRead parameter to true and obtain a strongly consistent result. Global secondary indexes support eventually consistent reads only, so do not specify ConsistentRead when querying a global secondary index.
Parameters:
-
table_name(TableArn) –The name of the table containing the requested items. You can also provide the Amazon Resource Name (ARN) of the table in this parameter.
-
index_name(Optional[IndexName], default:None) –The name of an index to query. This index can be any local secondary index or global secondary index on the table. Note that if you use the
IndexNameparameter, you must also provideTableName. -
select(Optional[Select], default:None) –The attributes to be returned in the result. You can retrieve all item attributes, specific item attributes, the count of matching items, or in the case of an index, some or all of the attributes projected into the index.
-
ALL_ATTRIBUTES- Returns all of the item attributes from the specified table or index. If you query a local secondary index, then for each matching item in the index, DynamoDB fetches the entire item from the parent table. If the index is configured to project all item attributes, then all of the data can be obtained from the local secondary index, and no fetching is required. -
ALL_PROJECTED_ATTRIBUTES- Allowed only when querying an index. Retrieves all attributes that have been projected into the index. If the index is configured to project all attributes, this return value is equivalent to specifyingALL_ATTRIBUTES. -
COUNT- Returns the number of matching items, rather than the matching items themselves. Note that this uses the same quantity of read capacity units as getting the items, and is subject to the same item size calculations. -
SPECIFIC_ATTRIBUTES- Returns only the attributes listed inProjectionExpression. This return value is equivalent to specifyingProjectionExpressionwithout specifying any value forSelect.If you query or scan a local secondary index and request only attributes that are projected into that index, the operation will read only the index and not the table. If any of the requested attributes are not projected into the local secondary index, DynamoDB fetches each of these attributes from the parent table. This extra fetching incurs additional throughput cost and latency.
If you query or scan a global secondary index, you can only request attributes that are projected into the index. Global secondary index queries cannot fetch attributes from the parent table.
If neither
SelectnorProjectionExpressionare specified, DynamoDB defaults toALL_ATTRIBUTESwhen accessing a table, andALL_PROJECTED_ATTRIBUTESwhen accessing an index. You cannot use bothSelectandProjectionExpressiontogether in a single request, unless the value forSelectisSPECIFIC_ATTRIBUTES. (This usage is equivalent to specifyingProjectionExpressionwithout any value forSelect.)If you use the
ProjectionExpressionparameter, then the value forSelectcan only beSPECIFIC_ATTRIBUTES. Any other value forSelectwill return an error. -
-
attributes_to_get(Optional[AttributeNameList], default:None) –This is a legacy parameter. Use
ProjectionExpressioninstead. For more information, see AttributesToGet in the Amazon DynamoDB Developer Guide. -
limit(Optional[PositiveIntegerObject], default:None) –The maximum number of items to evaluate (not necessarily the number of matching items). If DynamoDB processes the number of items up to the limit while processing the results, it stops the operation and returns the matching values up to that point, and a key in
LastEvaluatedKeyto apply in a subsequent operation, so that you can pick up where you left off. Also, if the processed dataset size exceeds 1 MB before DynamoDB reaches this limit, it stops the operation and returns the matching values up to the limit, and a key inLastEvaluatedKeyto apply in a subsequent operation to continue the operation. For more information, see Query and Scan in the Amazon DynamoDB Developer Guide. -
consistent_read(Optional[ConsistentRead], default:None) –Determines the read consistency model: If set to
true, then the operation uses strongly consistent reads; otherwise, the operation uses eventually consistent reads.Strongly consistent reads are not supported on global secondary indexes. If you query a global secondary index with
ConsistentReadset totrue, you will receive aValidationException. -
key_conditions(Optional[KeyConditions], default:None) –This is a legacy parameter. Use
KeyConditionExpressioninstead. For more information, see KeyConditions in the Amazon DynamoDB Developer Guide. -
query_filter(Optional[FilterConditionMap], default:None) –This is a legacy parameter. Use
FilterExpressioninstead. For more information, see QueryFilter in the Amazon DynamoDB Developer Guide. -
conditional_operator(Optional[ConditionalOperator], default:None) –This is a legacy parameter. Use
FilterExpressioninstead. For more information, see ConditionalOperator in the Amazon DynamoDB Developer Guide. -
scan_index_forward(Optional[BooleanObject], default:None) –Specifies the order for index traversal: If
true(default), the traversal is performed in ascending order; iffalse, the traversal is performed in descending order.Items with the same partition key value are stored in sorted order by sort key. If the sort key data type is Number, the results are stored in numeric order. For type String, the results are stored in order of UTF-8 bytes. For type Binary, DynamoDB treats each byte of the binary data as unsigned.
If
ScanIndexForwardistrue, DynamoDB returns the results in the order in which they are stored (by sort key value). This is the default behavior. IfScanIndexForwardisfalse, DynamoDB reads the results in reverse order by sort key value, and then returns the results to the client. -
exclusive_start_key(Optional[Key], default:None) –The primary key of the first item that this operation will evaluate. Use the value that was returned for
LastEvaluatedKeyin the previous operation.The data type for
ExclusiveStartKeymust be String, Number, or Binary. No set data types are allowed. -
projection_expression(Optional[ProjectionExpression], default:None) –A string that identifies one or more attributes to retrieve from the table. These attributes can include scalars, sets, or elements of a JSON document. The attributes in the expression must be separated by commas.
If no attribute names are specified, then all attributes will be returned. If any of the requested attributes are not found, they will not appear in the result.
For more information, see Accessing Item Attributes in the Amazon DynamoDB Developer Guide.
-
filter_expression(Optional[ConditionExpression], default:None) –A string that contains conditions that DynamoDB applies after the
Queryoperation, but before the data is returned to you. Items that do not satisfy theFilterExpressioncriteria are not returned.A
FilterExpressiondoes not allow key attributes. You cannot define a filter expression based on a partition key or a sort key.A
FilterExpressionis applied after the items have already been read; the process of filtering does not consume any additional read capacity units.For more information, see Filter Expressions in the Amazon DynamoDB Developer Guide.
-
key_condition_expression(Optional[KeyExpression], default:None) –The condition that specifies the key values for items to be retrieved by the
Queryaction.The condition must perform an equality test on a single partition key value.
The condition can optionally perform one of several comparison tests on a single sort key value. This allows
Queryto retrieve one item with a given partition key value and sort key value, or several items that have the same partition key value but different sort key values.The partition key equality test is required, and must be specified in the following format:
partitionKeyName=:partitionkeyvalIf you also want to provide a condition for the sort key, it must be combined using
ANDwith the condition for the sort key. Following is an example, using the = comparison operator for the sort key:partitionKeyName=:partitionkeyvalANDsortKeyName=:sortkeyvalValid comparisons for the sort key condition are as follows:
-
sortKeyName=:sortkeyval- true if the sort key value is equal to:sortkeyval. -
sortKeyName<:sortkeyval- true if the sort key value is less than:sortkeyval. -
sortKeyName<=:sortkeyval- true if the sort key value is less than or equal to:sortkeyval. -
sortKeyName>:sortkeyval- true if the sort key value is greater than:sortkeyval. -
sortKeyName>=:sortkeyval- true if the sort key value is greater than or equal to:sortkeyval. -
sortKeyNameBETWEEN:sortkeyval1AND:sortkeyval2- true if the sort key value is greater than or equal to:sortkeyval1, and less than or equal to:sortkeyval2. -
begins_with (sortKeyName,:sortkeyval)- true if the sort key value begins with a particular operand. (You cannot use this function with a sort key that is of type Number.) Note that the function namebegins_withis case-sensitive.
Use the
ExpressionAttributeValuesparameter to replace tokens such as:partitionvaland:sortvalwith actual values at runtime.You can optionally use the
ExpressionAttributeNamesparameter to replace the names of the partition key and sort key with placeholder tokens. This option might be necessary if an attribute name conflicts with a DynamoDB reserved word. For example, the followingKeyConditionExpressionparameter causes an error because Size is a reserved word:-
Size = :myval
To work around this, define a placeholder (such a
#S) to represent the attribute name Size.KeyConditionExpressionthen is as follows:-
#S = :myval
For a list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide.
For more information on
ExpressionAttributeNamesandExpressionAttributeValues, see Using Placeholders for Attribute Names and Values in the Amazon DynamoDB Developer Guide. -
-
expression_attribute_names(Optional[ExpressionAttributeNameMap], default:None) –One or more substitution tokens for attribute names in an expression. The following are some use cases for using
ExpressionAttributeNames:-
To access an attribute whose name conflicts with a DynamoDB reserved word.
-
To create a placeholder for repeating occurrences of an attribute name in an expression.
-
To prevent special characters in an attribute name from being misinterpreted in an expression.
Use the # character in an expression to dereference an attribute name. For example, consider the following attribute name:
-
Percentile
The name of this attribute conflicts with a reserved word, so it cannot be used directly in an expression. (For the complete list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide). To work around this, you could specify the following for
ExpressionAttributeNames:-
{"#P":"Percentile"}
You could then use this substitution in an expression, as in this example:
-
#P = :val
Tokens that begin with the : character are expression attribute values, which are placeholders for the actual value at runtime.
For more information on expression attribute names, see Specifying Item Attributes in the Amazon DynamoDB Developer Guide.
-
-
expression_attribute_values(Optional[ExpressionAttributeValueMap], default:None) –One or more values that can be substituted in an expression.
Use the : (colon) character in an expression to dereference an attribute value. For example, suppose that you wanted to check whether the value of the ProductStatus attribute was one of the following:
Available | Backordered | DiscontinuedYou would first need to specify
ExpressionAttributeValuesas follows:{ ":avail":{"S":"Available"}, ":back":{"S":"Backordered"}, ":disc":{"S":"Discontinued"} }You could then use these values in an expression, such as this:
ProductStatus IN (:avail, :back, :disc)For more information on expression attribute values, see Specifying Conditions in the Amazon DynamoDB Developer Guide.
Raises:
-
InternalServerError–An error occurred on the server side.
-
ProvisionedThroughputExceededException–The request was denied due to request throttling. For detailed information about why the request was throttled and the ARN of the impacted resource, find the ThrottlingReason field in the returned exception. The Amazon Web Services SDKs for DynamoDB automatically retry requests that receive this exception. Your request is eventually successful, unless your retry queue is too large to finish. Reduce the frequency of requests and use exponential backoff. For more information, go to Error Retries and Exponential Backoff in the Amazon DynamoDB Developer Guide.
-
RequestLimitExceeded–Throughput exceeds the current throughput quota for your account. For detailed information about why the request was throttled and the ARN of the impacted resource, find the ThrottlingReason field in the returned exception. Contact Amazon Web Services Support to request a quota increase.
-
ResourceNotFoundException–The operation tried to access a nonexistent table or index. The resource might not be specified correctly, or its status might not be
ACTIVE. -
ThrottlingException–The request was denied due to request throttling. For detailed information about why the request was throttled and the ARN of the impacted resource, find the ThrottlingReason field in the returned exception.
-
UnknownServiceError–The service returned an error code this client does not model.
Examples:
To query an item This example queries items in the Music table. The table has a partition key and sort key (Artist and SongTitle), but this query only specifies the partition key value. It returns song titles by the artist named "No One You Know".
>>> client.query(table_name='Music', projection_expression='SongTitle', key_condition_expression='Artist = :v1', expression_attribute_values={':v1': {'S': 'No One You Know'}})
Source code in docs_src/capo_dynamodb/_services/dynamo_db.py
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