The STRING
data type stores a string of Unicode characters.
Aliases
In CockroachDB, the following are aliases for STRING
:
CHARACTER
CHAR
VARCHAR
TEXT
And the following are aliases for STRING(n)
:
CHARACTER(n)
CHARACTER VARYING(n)
CHAR(n)
CHAR VARYING(n)
VARCHAR(n)
Length
To limit the length of a string column, use STRING(n)
, where n
is the maximum number of Unicode code points (normally thought of as "characters") allowed.
When inserting a string:
- If the value exceeds the column's length limit, CockroachDB gives an error.
- If the value is cast as a string with a length limit (e.g.,
CAST('hello world' AS STRING(5))
), CockroachDB truncates to the limit. - If the value is under the column's length limit, CockroachDB does not add padding. This applies to
STRING(n)
and all its aliases.
Syntax
A value of type STRING
can be expressed using a variety of formats.
See string literals for more details.
When printing out a STRING
value in the SQL shell, the shell uses the simple
SQL string literal format if the value doesn't contain special character,
or the escaped format otherwise.
Collations
STRING
values accept collations, which lets you sort strings according to language- and country-specific rules.
Size
The size of a STRING
value is variable, but it's recommended to keep values under 64 kilobytes to ensure performance. Above that threshold, write amplification and other considerations may cause significant performance degradation.
Examples
> CREATE TABLE strings (a STRING PRIMARY KEY, b STRING(4), c TEXT);
> SHOW COLUMNS FROM strings;
column_name | data_type | is_nullable | column_default | generation_expression | indices | is_hidden
+-------------+-----------+-------------+----------------+-----------------------+-------------+-----------+
a | STRING | false | NULL | | {"primary"} | false
b | STRING(4) | true | NULL | | {} | false
c | STRING | true | NULL | | {} | false
(3 rows)
> INSERT INTO strings VALUES ('a1b2c3d4', 'e5f6', 'g7h8i9');
> SELECT * FROM strings;
a | b | c
+----------+------+--------+
a1b2c3d4 | e5f6 | g7h8i9
(1 row)
> CREATE TABLE aliases (a STRING PRIMARY KEY, b VARCHAR, c CHAR);
> SHOW COLUMNS FROM aliases;
column_name | data_type | is_nullable | column_default | generation_expression | indices | is_hidden
+-------------+-----------+-------------+----------------+-----------------------+-------------+-----------+
a | STRING | false | NULL | | {"primary"} | false
b | VARCHAR | true | NULL | | {} | false
c | CHAR | true | NULL | | {} | false
(3 rows)
Supported casting and conversion
STRING
values can be cast to any of the following data types:
Type | Details |
---|---|
BOOL |
Requires supported BOOL string format, e.g., 'true' . |
BYTES |
For more details, see here. |
DATE |
Requires supported DATE string format, e.g., '2016-01-25' . |
DECIMAL |
Requires supported DECIMAL string format, e.g., '1.1' . |
FLOAT |
Requires supported FLOAT string format, e.g., '1.1' . |
INET |
Requires supported INET string format, e.g, '192.168.0.1' . |
INT |
Requires supported INT string format, e.g., '10' . |
INTERVAL |
Requires supported INTERVAL string format, e.g., '1h2m3s4ms5us6ns' . |
TIME |
Requires supported TIME string format, e.g., '01:22:12' (microsecond precision). |
TIMESTAMP |
Requires supported TIMESTAMP string format, e.g., '2016-01-25 10:10:10.555555' . |
STRING
vs. BYTES
While both STRING
and BYTES
can appear to have similar behavior in many situations, one should understand their nuance before casting one into the other.
STRING
treats all of its data as characters, or more specifically, Unicode code points. BYTES
treats all of its data as a byte string. This difference in implementation can lead to dramatically different behavior. For example, let's take a complex Unicode character such as ☃ (the snowman emoji):
> SELECT length('☃'::string);
length
+--------+
1
> SELECT length('☃'::bytes);
length
+--------+
3
In this case, LENGTH(string)
measures the number of Unicode code points present in the string, whereas LENGTH(bytes)
measures the number of bytes required to store that value. Each character (or Unicode code point) can be encoded using multiple bytes, hence the difference in output between the two.
Translating literals to STRING
vs. BYTES
A literal entered through a SQL client will be translated into a different value based on the type:
BYTES
give a special meaning to the pair\x
at the beginning, and translates the rest by substituting pairs of hexadecimal digits to a single byte. For example,\xff
is equivalent to a single byte with the value of 255. For more information, see SQL Constants: String literals with character escapes.STRING
does not give a special meaning to\x
, so all characters are treated as distinct Unicode code points. For example,\xff
is treated as aSTRING
with length 4 (\
,x
,f
, andf
).