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Literal Values

About 2 min

Literal Values

This section describes how to write literal values in IoTDB. These include strings, numbers, timestamp values, boolean values, and NULL.

String Literals

in IoTDB, A string is a sequence of bytes or characters, enclosed within either single quote (') or double quote (") characters. Examples:

'a string'
"another string"

Usage Scenarios

Usages of string literals:

  • Values of TEXT type data in INSERT or SELECT statements

    # insert
    insert into root.ln.wf02.wt02(timestamp,hardware) values(1, 'v1')
    insert into root.ln.wf02.wt02(timestamp,hardware) values(2, '\\')
    
    +-----------------------------+--------------------------+
    |                         Time|root.ln.wf02.wt02.hardware|
    +-----------------------------+--------------------------+
    |1970-01-01T08:00:00.001+08:00|                        v1|
    +-----------------------------+--------------------------+
    |1970-01-01T08:00:00.002+08:00|                        \\|
    +-----------------------------+--------------------------+
    
    # select
    select code from root.sg1.d1 where code in ('string1', 'string2');
    
  • Used inLOAD / REMOVE / SETTLE instructions to represent file path.

    # load
    LOAD 'examplePath'
    
    # remove
    REMOVE 'examplePath'
    
    # SETTLE
    SETTLE 'examplePath'
    
  • Password fields in user management statements

    # write_pwd is the password
    CREATE USER ln_write_user 'write_pwd'
    
  • Full Java class names in UDF and trigger management statements

    # Trigger example. Full java class names after 'AS' should be string literals.
    CREATE TRIGGER `alert-listener-sg1d1s1`
    AFTER INSERT
    ON root.sg1.d1.s1
    AS 'org.apache.iotdb.db.engine.trigger.example.AlertListener'
    WITH (
      'lo' = '0', 
      'hi' = '100.0'
    )
    
    # UDF example. Full java class names after 'AS' should be string literals.
    CREATE FUNCTION example AS 'org.apache.iotdb.udf.UDTFExample'
    
  • AS function provided by IoTDB can assign an alias to time series selected in query. Alias can be constant(including string) or identifier.

    select s1 as 'temperature', s2 as 'speed' from root.ln.wf01.wt01;
    
    # Header of dataset
    +-----------------------------+-----------|-----+
    |                         Time|temperature|speed|
    +-----------------------------+-----------|-----+
    
  • The key/value of an attribute can be String Literal and identifier, more details can be found at key-value pair part.

How to use quotation marks in String Literals

There are several ways to include quote characters within a string:

  • ' inside a string quoted with " needs no special treatment and need not be doubled or escaped. In the same way, " inside a string quoted with ' needs no special treatment.
  • A ' inside a string quoted with ' may be written as ''.
  • A " inside a string quoted with " may be written as "".

The following examples demonstrate how quoting and escaping work:

'string'  // string
'"string"'  // "string"
'""string""'  // ""string""
'''string'  // 'string

"string" // string
"'string'"  // 'string'
"''string''"  // ''string''
"""string"  // "string

Numeric Literals

Number literals include integer (exact-value) literals and floating-point (approximate-value) literals.

Integers are represented as a sequence of digits. Numbers may be preceded by - or + to indicate a negative or positive value, respectively. Examples: 1, -1.

Numbers with fractional part or represented in scientific notation with a mantissa and exponent are approximate-value numbers. Examples: .1, 3.14, -2.23, +1.70, 1.2E3, 1.2E-3, -1.2E3, -1.2E-3.

The INT32 and INT64 data types are integer types and calculations are exact.

The FLOAT and DOUBLE data types are floating-point types and calculations are approximate.

An integer may be used in floating-point context; it is interpreted as the equivalent floating-point number.

Timestamp Literals

The timestamp is the time point at which data is produced. It includes absolute timestamps and relative timestamps in IoTDB. For information about timestamp support in IoTDB, see Data Type Doc.

Specially, NOW() represents a constant timestamp that indicates the system time at which the statement began to execute.

Boolean Literals

The constants TRUE and FALSE evaluate to 1 and 0, respectively. The constant names can be written in any lettercase.

NULL Values

The NULL value means “no data.” NULL can be written in any lettercase.

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