On 14/05/2009 12:23 AM, Salvatore Di Guida wrote:
> Hi all!
> Since I am a newcomer in SQLite, as a preliminary question, what is the
> difference between
> sqlite> select length(X'01');
> and
> sqlite> select length('01');
> It seems that the former gives the size in bytes, the latter the length of
> the string.
>
> The SQLite documentation says that the length function returns the
> string length of /X/ in characters if /X/ is a string, or in bytes if
> /X/ is a blob.
The concept "blob length in characters" is meaningless. The first "b" in
"blob" means "Binary". A blob contains whatever you know/hope it
contains, or something completely different ... it could be an 80-bit
float or a 128-bit integer; it could be some complicated structure that
you have serialised; etc etc. Only the length in bytes has any meaning.
"Characters" have meaning only with TEXT data. A (Unicode) character
will occupy 1, 2, or 3 bytes depending on the character itself, if
encoded in UTF-8 (the SQLite default); 2 bytes if UTF-16.
>
> However, I tried this example:
>
> sqlite3 test.db
>
> SQLite version 3.6.10
>
> Enter ".help" for instructions
>
> Enter SQL statements terminated with a ";"
>
> sqlite> create table x ( a TEXT, b BLOB );
>
> sqlite> insert into x values ( 'a', 'a' );
I see no blobs here.
>
> sqlite> insert into x values ( 'abcd', 'abcd' );
Nor here.
Igor has already pointed you at http://www.sqlite.org/datatype3.html --
do read it carefully and ask questions here if some of it is puzzling.
>
> sqlite> select length(a), length(b) from x;
>
> 1|1
>
> 4|4
>
>
> The length function, then, measures the length in characters of the
> blob.
That is a non sequitur, to put it mildly.
> What can I do in order to obtain the size in bytes of the blob?
length(the_blob)
HTH,
John
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