The Query operation finds items based on primary key values. You can
query any table or secondary index that has a composite primary key (a
partition key and a sort key).
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.
dynamodb_query(TableName, IndexName, Select, AttributesToGet, Limit,
ConsistentRead, KeyConditions, QueryFilter, ConditionalOperator,
ScanIndexForward, ExclusiveStartKey, ReturnConsumedCapacity,
ProjectionExpression, FilterExpression, KeyConditionExpression,
ExpressionAttributeNames, ExpressionAttributeValues)[required] The name of the table containing the requested items.
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
IndexName parameter, you must also provide TableName.
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 specifying ALL_ATTRIBUTES.
COUNT - Returns the number of matching items, rather than the
matching items themselves.
SPECIFIC_ATTRIBUTES - Returns only the attributes listed in
AttributesToGet. This return value is equivalent to specifying
AttributesToGet without specifying any value for Select.
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 Select nor AttributesToGet are specified, DynamoDB
defaults to ALL_ATTRIBUTES when accessing a table, and
ALL_PROJECTED_ATTRIBUTES when accessing an index. You cannot use both
Select and AttributesToGet together in a single request, unless the
value for Select is SPECIFIC_ATTRIBUTES. (This usage is equivalent
to specifying AttributesToGet without any value for Select.)
If you use the ProjectionExpression parameter, then the value for
Select can only be SPECIFIC_ATTRIBUTES. Any other value for Select
will return an error.
This is a legacy parameter. Use ProjectionExpression instead. For more
information, see
AttributesToGet
in the Amazon DynamoDB Developer Guide.
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 LastEvaluatedKey to
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 in LastEvaluatedKey to apply in a
subsequent operation to continue the operation. For more information,
see Query and Scan
in the Amazon DynamoDB Developer Guide.
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 ConsistentRead set to
true, you will receive a ValidationException.
This is a legacy parameter. Use KeyConditionExpression instead. For
more information, see
KeyConditions
in the Amazon DynamoDB Developer Guide.
This is a legacy parameter. Use FilterExpression instead. For more
information, see
QueryFilter
in the Amazon DynamoDB Developer Guide.
This is a legacy parameter. Use FilterExpression instead. For more
information, see
ConditionalOperator
in the Amazon DynamoDB Developer Guide.
Specifies the order for index traversal: If true (default), the
traversal is performed in ascending order; if false, 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 ScanIndexForward is true, DynamoDB returns the results in the
order in which they are stored (by sort key value). This is the default
behavior. If ScanIndexForward is false, DynamoDB reads the results
in reverse order by sort key value, and then returns the results to the
client.
The primary key of the first item that this operation will evaluate. Use
the value that was returned for LastEvaluatedKey in the previous
operation.
The data type for ExclusiveStartKey must be String, Number, or Binary.
No set data types are allowed.
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.
A string that contains conditions that DynamoDB applies after the
Query operation, but before the data is returned to you. Items that do
not satisfy the FilterExpression criteria are not returned.
A FilterExpression does not allow key attributes. You cannot define a
filter expression based on a partition key or a sort key.
A FilterExpression is 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.
The condition that specifies the key values for items to be retrieved by
the Query action.
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 Query to 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 = :partitionkeyval
If you also want to provide a condition for the sort key, it must be
combined using AND with the condition for the sort key. Following is
an example, using the = comparison operator for the sort key:
partitionKeyName = :partitionkeyval AND sortKeyName =
:sortkeyval
Valid 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.
sortKeyName BETWEEN :sortkeyval1 AND :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 name begins_with is case-sensitive.
Use the ExpressionAttributeValues parameter to replace tokens such as
:partitionval and :sortval with actual values at runtime.
You can optionally use the ExpressionAttributeNames parameter 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 following
KeyConditionExpression parameter 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. KeyConditionExpression then is as follows:
#S = :myval
For a list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide.
For more information on ExpressionAttributeNames and
ExpressionAttributeValues, see Using Placeholders for Attribute Names and Values
in the Amazon DynamoDB Developer Guide.
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.
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 | Discontinued
You would first need to specify ExpressionAttributeValues as 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.
svc$query(
TableName = "string",
IndexName = "string",
Select = "ALL_ATTRIBUTES"|"ALL_PROJECTED_ATTRIBUTES"|"SPECIFIC_ATTRIBUTES"|"COUNT",
AttributesToGet = list(
"string"
),
Limit = 123,
ConsistentRead = TRUE|FALSE,
KeyConditions = list(
list(
AttributeValueList = list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
),
ComparisonOperator = "EQ"|"NE"|"IN"|"LE"|"LT"|"GE"|"GT"|"BETWEEN"|"NOT_NULL"|"NULL"|"CONTAINS"|"NOT_CONTAINS"|"BEGINS_WITH"
)
),
QueryFilter = list(
list(
AttributeValueList = list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
),
ComparisonOperator = "EQ"|"NE"|"IN"|"LE"|"LT"|"GE"|"GT"|"BETWEEN"|"NOT_NULL"|"NULL"|"CONTAINS"|"NOT_CONTAINS"|"BEGINS_WITH"
)
),
ConditionalOperator = "AND"|"OR",
ScanIndexForward = TRUE|FALSE,
ExclusiveStartKey = list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
),
ReturnConsumedCapacity = "INDEXES"|"TOTAL"|"NONE",
ProjectionExpression = "string",
FilterExpression = "string",
KeyConditionExpression = "string",
ExpressionAttributeNames = list(
"string"
),
ExpressionAttributeValues = list(
list(
S = "string",
N = "string",
B = raw,
SS = list(
"string"
),
NS = list(
"string"
),
BS = list(
raw
),
M = list(
list()
),
L = list(
list()
),
NULL = TRUE|FALSE,
BOOL = TRUE|FALSE
)
)
)
# NOT RUN {
# This example queries items in the Music table. The table has a partition
# key and sort key (Artist and SongTitle), but this query only specifies
# the partition key value. It returns song titles by the artist named "No
# One You Know".
svc$query(
ExpressionAttributeValues = list(
`:v1` = list(
S = "No One You Know"
)
),
KeyConditionExpression = "Artist = :v1",
ProjectionExpression = "SongTitle",
TableName = "Music"
)
# }
# NOT RUN {
# }
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