9.5. 位元字串函式及運算子
This section describes functions and operators for examining and manipulating values of type bytea
.
SQL defines some string functions that use key words, rather than commas, to separate arguments. Details are in Table 9.12. PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9.13).
Note
The sample results shown on this page assume that the server parameter bytea_output
is set to escape
(the traditional PostgreSQL format).
Table 9.12. SQL Binary String Functions and Operators
Additional binary string manipulation functions are available and are listed in Table 9.13. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.12.
Table 9.13. Other Binary String Functions
get_byte
and set_byte
number the first byte of a binary string as byte 0. get_bit
and set_bit
number bits from the right within each byte; for example bit 0 is the least significant bit of the first byte, and bit 15 is the most significant bit of the second byte.
Note that for historic reasons, the function md5
returns a hex-encoded value of type text
whereas the SHA-2 functions return type bytea
. Use the functions encode
and decode
to convert between the two, for example encode(sha256('abc'), 'hex')
to get a hex-encoded text representation.
See also the aggregate function string_agg
in Section 9.20 and the large object functions in Section 34.4.
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