Identifiers

August 1, 2023About 4 min

Identifiers

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.

Identifier

Usage scenarios

Certain objects within IoTDB, including TRIGGER, FUNCTION(UDF), CONTINUOUS QUERY, SCHEMA TEMPLATE, USER, ROLE,Pipe,PipeSink,alias and other object names are known as identifiers.

Constraints

Below are basic constraints of identifiers, specific identifiers may have other constraints, for example, user should consists of more than 4 characters.

Permitted characters in unquoted identifiers:
- [0-9 a-z A-Z _ ] (letters, digits and underscore)
- ['\u2E80'..'\u9FFF'] (UNICODE Chinese characters)

Reverse quotation marks

If the following situations occur, the identifier needs to be quoted using reverse quotes:

The identifier contains special characters that are not allowed.
The identifier is a real number.

How to use quotation marks in identifiers caused by reverse quotation marks

Single and double quotes can be directly used in identifiers caused by reverse quotes.

In identifiers referenced with quotation marks, quotation marks can be used by double writing them, meaning ` can be represented as``.

example：

# Create Template t1 ` t
create device template `t1``t` 
(temperature FLOAT encoding=RLE, status BOOLEAN encoding=PLAIN compression=SNAPPY)

# Create Template t1't "t
create device template `t1't"t` 
(temperature FLOAT encoding=RLE, status BOOLEAN encoding=PLAIN compression=SNAPPY)

Examples of Reverse Quotation Marks

When the trigger name encounters the above special situations, reverse quotation marks should be used to reference it:

# Create trigger alert.` listener-sg1d1s1
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'
)

When the UDF name encounters the above special situations, reverse quotation marks should be used for reference:

# Create a UDF named 111, which is a real number and needs to be quoted in reverse quotation marks.
CREATE FUNCTION `111` AS 'org.apache.iotdb.udf.UDTFExample'

When the metadata template name encounters the above special situations, reverse quotation marks should be used for reference:

# Create a metadata template named 111, where 111 is a real number and needs to be quoted in reverse quotation marks.
create device template `111` 
(temperature FLOAT encoding=RLE, status BOOLEAN encoding=PLAIN compression=SNAPPY)

When the username and role name encounter the above special situations, reverse quotation marks should be used for reference. Regardless of whether reverse quotation marks are used or not, spaces are not allowed in the username and role name. Please refer to the instructions in the permission management section for details.
```
# Create user special ` user.
CREATE USER `special``user.` 'write_pwd'

# Create Character 111
CREATE ROLE `111`
```

When encountering the above special situations in continuous query identification, reverse quotation marks should be used to reference:

# Create continuous query test.cq
CREATE CONTINUOUS QUERY `test.cq` 
BEGIN 
  SELECT max_value(temperature) 
  INTO temperature_max 
  FROM root.ln.*.* 
  GROUP BY time(10s) 
END

When the names Pipe and PipeSink encounter the above special situations, reverse quotation marks should be used for reference:

# Create PipeSink test. * 1
CREATE PIPESINK `test.*1` AS IoTDB ('ip' = '输入你的IP')

# Create Pipe Test. * 2
CREATE PIPE `test.*2` TO `test.*1` FROM 
(select ** from root WHERE time>=yyyy-mm-dd HH:MM:SS) WITH 'SyncDelOp' = 'true'

In the Select clause, an alias can be specified for the value in the result set, which can be defined as a string or identifier. Examples are as follows:

select s1 as temperature, s2 as speed from root.ln.wf01.wt01;
# 表头如下所示
+-----------------------------+-----------+-----+
|                         Time|temperature|speed|
+-----------------------------+-----------+-----+

Used to represent key value pairs, the keys and values of key value pairs can be defined as constants (including strings) or identifiers. Please refer to the Key Value Pair section for details.
Non database nodes in the path are allowed to contain the symbol *. When using it, the node needs to be enclosed in reverse quotes (as shown below), but this usage is only recommended when the path inevitably contains *.
```
`root.db.*`
```