the doc of Postgres Ltree said that
A label is a sequence of alphanumeric characters and underscores (for example, in C locale the characters A-Za-z0-9_ are allowed). Labels must be less than 256 bytes long.
However, it does not said that if we set the locale to 'en_US.UTF-8', what is the valid character can be used in Postgres Ltree. So, can dash(hyphen) be used in the label of Ltree?
Sorry for not updating the answer.
Yes, i have finally figured out that it is one of our DBA that changed the source of ltree and recompile it with supporting the dash(-) char. We have a single table with more than 6B records.
Related
I have a table in my Postgres DB. In this table, there is a column city this column has type character and length 255.
When I try to add a city in this column, for example, London and after that, I try to get this city I get a value with 255 lengths.
Looks likes [London....................-255] where dots are empty characters
When I add value in db always doing trim.
I use pg for node js
As the comment says, you don't want to use character(255) as the field type, which is always 255 characters, padded with whitespace.
Instead, you might consider using varchar(255), but even so, you probably don't actually want to limit the length here – Postgres doesn't care, storage-wise!, whereas MySQL does – so just use text.
we are in a phase of migration of some tables from AS400 DB to DB2 LUW(V11.1).
While migrating we found some special character(€) in the source database(AS400)- (Column with CHAR) and that lead to error if we are unable to alter table column with CODEUNITS32, DB2 LUW Database configuration Byte Encoding Set at UTF-8.
We want to understand, what would be the behavior of the application after changing the char column to CODEUNITS32, Do I need to update any Configuration at the application level (C & Java Application) to handle both Character Encoding Set?
After changing to CODEUNITS32
- My C application able to compile and able to handle change in Character byte from 8 bit per character(UTF-8) to 4 Byte Per Character(CODEUNITS32)?
- My Java application is able to handle change in Character byte from 8 bit per character(UTF-8) to 4 Byte Per Character(CODEUNITS32)?
We did some pilot testing by inserting Special character manually to the table after setting column definition to CODEUNITS32 from CHAR and testing was successful.
Using a string units specification of CODEUNITS32 for a column does not change the encoding of a column, the data is still stored in UTF-8 for CHAR/VARCHAR columns.
It alters the physical length (CHAR) or max length (VARCHAR) of the column by a factor of 4.
It also enables "character semantics" in some functions such as SUBSTR(), such that they work on characters, not bytes when processing CODEUNITS32 columns. (SUBSTRING() will always use character semantics (unless processing a FOR BIT DATA column))
So a CHAR(4) is CHAR(4 OCTETS) is 4 bytes long, and can hold at most 4 characters if they are all single byte in UTF-8. For € which is 3 bytes long, it could only hold say €4 but not €42
ACHAR(4 CODEUNTIS32) is 16 bytes long, and is allowed to hold up to 4 characters. It could hold €€€€ but not €2345
It is worth considering avoiding CHAR(x CODEUNITS32) and prefering VARCHAR(x CODEUNITS32). UTF-8 does not really play well with fixed width data types. The more common UTF-8 characters are 1 or 2 bytes long, so typically a CHAR(x CODEUNITS32) column will hold be more than 50% space padding.
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.1.0/com.ibm.db2.luw.sql.ref.doc/doc/r0008470.html
CODEUNITS32
Indicates that the units for the length attribute are Unicode UTF-32 code units which approximate counting in characters.
This unit of length does not affect the underlying code page of the data type.
The actual length of a data value is determined by counting the UTF-32
code units as if the data was converted to UTF-32.
A string unit of CODEUNITS32 can be used only in a Unicode database.
CODEUNITS32 can be
explicitly specified or determined based on an environment setting.
Also, out of interest, GRAPHIC/VARGRAPHIC and columns are stored in UTF-16, and default to CODEUNITS16, but can also use CODEUNITS32.
https://www.ibm.com/support/knowledgecenter/en/SSEPGG_11.1.0/com.ibm.db2.luw.sql.ref.doc/doc/r0008471.html
I'm migrating from MySQL to PostgreSQL because Oracle. There is a great MySQL text type reference, here is the relevant information for MySQL...
CHAR( ) A fixed section from 0 to 255 characters long.
VARCHAR( ) A variable section from 0 to 255 characters long.
TINYTEXT A string with a maximum length of 255 characters.
TEXT A string with a maximum length of 65535 characters.
BLOB A string with a maximum length of 65535 characters.
MEDIUMTEXT A string with a maximum length of 16777215 characters.
MEDIUMBLOB A string with a maximum length of 16777215 characters.
LONGTEXT A string with a maximum length of 4294967295 characters.
LONGBLOB A string with a maximum length of 4294967295 characters.
PostgreSQL seems a bit different, there is a text type looking through phppgAdmin, not sure what else there is and I'm not finding any good comparison tables.
What are all the available text types in PostgreSQL?
PostgreSQL has more advanced types but doesn't need the distinction between text sizes.
There are 3 string types in PostgreSQL and a binary type:
text
Just a text object with a non-specified size. You can put anything in here and it will be stored. Size doesn't matter.
varchar(n) / character varying(n)
Basically a text which has a size check, there is virtually no (except for checking the size while inserting) performance difference here.
char(n) / character(n)
Just a text where all the extra characters will be padded with space characters so you always get n characters back.
bytea
The blob type you've mentioned is a totally different type alltogether. You could replace it with the bytea type: http://www.postgresql.org/docs/9.3/static/datatype-binary.html
Source: http://www.postgresql.org/docs/9.3/static/datatype-character.html
I have a 1,000,000 rows plus string table, that has some garbage inside due to encoding errors.
The garbage is minimal, but needs to be found.
The column in question is a NVARCHAR column that normally contains text in one of 11 languages.
All of the text should be unicode (utf-8 when we process it application side).
The corrupt columns contain ? characters and or a very limited unusual glyph set, by eye they can be very easily seen not to be valid language. It is likely that these columns have been encoded backwards and forwards into total garbage.
So in the name of speed, is there anything I can do on SQL Server to detect bad encoding / string garbage?
Thanks.
EDIT to add garbage example:
This was Russian или Ð˜Ð¼Ñ Ð£Ñ‡Ð°Ñтника
I don't have much experience with MS SQL server 2008 R2 but here is the issue if you would help me please:
I have a table with a column/field (type : nvarchar) that stores text. The text is read from a text file and written to the database using vb.net application.
The text in the text file contains Turkish characters such as the u with 2 dots on top(in the future it will be in different languages )
When I open the table, the text in the column is not readable. It converts the Turkish special character to some unreadable characters.
Is there anyway to make the text readable in the table?
Thank you so much.
SQL Server doesn't change any character stored in tables, I think the problem is displaying the text in different character set. Try using UTF-8 character set.