Condition and filter expressions, operators, and functions in DynamoDB (original) (raw)

To manipulate data in an DynamoDB table, you use the PutItem, UpdateItem, andDeleteItem operations. For these data manipulation operations, you can specify a condition expression to determine which items should be modified. If the condition expression evaluates to true, the operation succeeds. Otherwise, the operation fails.

This section covers the built-in functions and keywords for writing filter expressions and condition expressions in Amazon DynamoDB. For more detailed information on functions and programming with DynamoDB, see Programming with DynamoDB and the AWS SDKs and the DynamoDB API Reference.

Topics

• Syntax for filter and condition expressions
• Making comparisons
• Functions
• Logical evaluations
• Parentheses
• Precedence in conditions

Syntax for filter and condition expressions

In the following syntax summary, an operand can be the following:

• A top-level attribute name, such as Id, Title,Description, or ProductCategory
• A document path that references a nested attribute

condition-expression ::=
      operand comparator operand
    | operand BETWEEN operand AND operand
    | operand IN ( operand (',' operand (, ...) ))
    | function
    | condition AND condition
    | condition OR condition
    | NOT condition
    | ( condition )

comparator ::=
    =
    | <>
    | <
    | <=
    | >
    | >=

function ::=
    attribute_exists (path)
    | attribute_not_exists (path)
    | attribute_type (path, type)
    | begins_with (path, substr)
    | contains (path, operand)
    | size (path)

Making comparisons

Use these comparators to compare an operand against a single value:

• `a` = `b` – True if a is equal tob.
• `a` <>`b` – True ifa is not equal tob.
• `a` < `b` – True if a is less thanb.
• `a` <= `b` – True if a is less than or equal tob.
• `a` > `b` – True if a is greater thanb.
• `a` >= `b` – True if a is greater than or equal tob.

Use the BETWEEN and IN keywords to compare an operand against a range of values or an enumerated list of values:

• `a` BETWEEN `b` AND`c` – True ifa is greater than or equal tob, and less than or equal toc.
• `a` IN (`b`,`c`, `d`) – True if a is equal to any value in the list—for example, any of b,c, or d. The list can contain up to 100 values, separated by commas.

Functions

Use the following functions to determine whether an attribute exists in an item, or to evaluate the value of an attribute. These function names are case sensitive. For a nested attribute, you must provide its full document path.

Logical evaluations

Use the AND, OR, and NOT keywords to perform logical evaluations. In the following list, a andb represent conditions to be evaluated.

• `a` AND `b` – True if a and b are both true.
• `a` OR `b` – True if either a orb (or both) are true.
• NOT `a` – True ifa is false. False if a is true.

The following is a code example of AND in an operation.

dynamodb-local (*)> select * from exprtest where a > 3 and a < 5;

Parentheses

Use parentheses to change the precedence of a logical evaluation. For example, suppose that conditions a and b are true, and that condition c is false. The following expression evaluates to true:

• `a` OR `b` AND`c`

However, if you enclose a condition in parentheses, it is evaluated first. For example, the following evaluates to false:

• (`a` OR `b`) AND`c`

Note

You can nest parentheses in an expression. The innermost ones are evaluated first.

The following is a code example with parentheses in a logical evaluation.

dynamodb-local (*)> select * from exprtest where attribute_type(b, string) or ( a = 5 and c = “coffee”);

Precedence in conditions

DynamoDB evaluates conditions from left to right using the following precedence rules:

• = <> < <= > >=
• IN
• BETWEEN
• attribute_exists attribute_not_exists begins_with contains
• Parentheses
• NOT
• AND
• OR