The BYTES
data type stores binary strings of variable length.
Aliases
In CockroachDB, the following are aliases for BYTES
:
BYTEA
BLOB
Syntax
To express a byte array constant, see the section on
byte array literals for more
details. For example, the following three are equivalent literals for the same
byte array: b'abc'
, b'\141\142\143'
, b'\x61\x62\x63'
.
In addition to this syntax, CockroachDB also supports using
string literals, including the
syntax '...'
, e'...'
and x'....'
in contexts where a byte array
is otherwise expected.
Size
The size of a BYTES
value is variable, but it's recommended to keep values under 1 MB to ensure performance. Above that threshold, write amplification and other considerations may cause significant performance degradation.
Example
> CREATE TABLE bytes (a INT PRIMARY KEY, b BYTES);
> -- explicitly typed BYTES literals
> INSERT INTO bytes VALUES (1, b'\141\142\143'), (2, b'\x61\x62\x63'), (3, b'\141\x62\c');
> -- string literal implicitly typed as BYTES
> INSERT INTO bytes VALUES (4, 'abc');
> SELECT * FROM bytes;
+---+-----+
| a | b |
+---+-----+
| 1 | abc |
| 2 | abc |
| 3 | abc |
| 4 | abc |
+---+-----+
(4 rows)
Supported conversions
BYTES
values can be
cast explicitly to
STRING
. This conversion always succeeds. Two
conversion modes are supported, controlled by the
session variable bytea_output
:
hex
(default): The output of the conversion starts with the two characters\
,x
and the rest of the string is composed by the hexadecimal encoding of each byte in the input. For example,x'48AA'::STRING
produces'\x48AA'
.escape
: The output of the conversion contains each byte in the input, as-is if it is an ASCII character, or encoded using the octal escape format\NNN
otherwise. For example,x'48AA'::STRING
produces'0\252'
.
STRING
values can be cast explicitly to BYTES
. This conversion
will fail if the hexadecimal digits are not valid, or if there is an
odd number of them. Two conversion modes are supported:
If the string starts with the two special characters
\
andx
(e.g.,\xAABB
), the rest of the string is interpreted as a sequence of hexadecimal digits. The string is then converted to a byte array where each pair of hexadecimal digits is converted to one byte.Otherwise, the string is converted to a byte array that contains its UTF-8 encoding.
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
).