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Expression Syntax

ksqlDB supports the following syntax to define WHERE expressions.

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expr:
    expr AND expr
  | expr OR expr
  | NOT expr
  | predicate

predicate:
    value_expr comparison_operator value_expr
  | value_expr [NOT] BETWEEN value_expr AND value_expr  
  | value_expr [NOT] LIKE value_expr [ESCAPE string]
  | value_expr IS [NOT] NULL
  | value_expr IS [NOT] DISTINCT FROM value_expr

comparison_operator: EQ | NEQ | LT | LTE | GT | GTE

value_expr:
    primary_expr
  | + value_expr
  | - value_expr
  | value_expr + value_expr
  | value_expr - value_expr
  | value_expr * value_expr
  | value_expr / value_expr
  | value_expr % value_expr
  | value_expr AT timezone
  | value_expr CONCAT value_expr

primary_expr:
    literal
  | identifier
  | function_call
  | case_expr
  | cast_expr

arithmetic_operator: + | - | * | / | %

Operators

ksqlDB supports the following operators in value expressions.

Arithmetic

The usual arithmetic operators (+,-,/,*,%) may be applied to numeric types, like INT, BIGINT, and DOUBLE:

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SELECT USERID, LEN(FIRST_NAME) + LEN(LAST_NAME) AS NAME_LENGTH FROM USERS EMIT CHANGES;

Concatenation

The concatenation operator (+,||) can be used to concatenate STRING values.

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SELECT USERID, FIRST_NAME + LAST_NAME AS FULL_NAME FROM USERS EMIT CHANGES;

You can use the + operator for multi-part concatenation, for example:

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SELECT USERID,
    TIMESTAMPTOSTRING(ROWTIME, 'yyyy-MM-dd HH:mm:ss') +
        ': :heavy_exclamation_mark: On ' +
        HOST +
        ' there were ' +
        CAST(INVALID_LOGIN_COUNT AS VARCHAR) +
        ' attempts in the last minute (threshold is >=4)'
  FROM INVALID_USERS_LOGINS_PER_HOST
  WHERE INVALID_LOGIN_COUNT>=4
  EMIT CHANGES;

Source Dereference

The source dereference operator (.) can be used to specify columns by dereferencing the source stream or table.

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SELECT USERID, USERS.FIRST_NAME FROM USERS EMIT CHANGES;

Subscript

The subscript operator ([subscript_expr]) is used to reference the value at an array index or a map key.

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SELECT USERID, NICKNAMES[1] FROM USERS EMIT CHANGES;

STRUCT dereference

Access nested data by declaring a STRUCT and using the dereference operator (->) to access its fields:

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SELECT USERID, ADDRESS->STREET, ADDRESS->HOUSE_NUM FROM USERS EMIT CHANGES;

Access all STRUCT fields by using a * in the derefence operator:

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SELECT USERID, ADDRESS->* FROM USERS EMIT CHANGES;

Combine -> with . when using aliases:

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SELECT USERID, USERS.ADDRESS->STREET, U.ADDRESS->STREET FROM USERS U EMIT CHANGES;

For more information on nested data, see STRUCT.

Last update: 2022-08-19