Character Datatypes

NLS parameters (V$NLS_PARAMETERS)

NLS_LENGTH_SEMANTICS
1. BYTE (default)
2. CHAR
NLS_CHARACTERSET
Character encoding of CHAR, VARCHAR2 and CLOB datatypes
eg: AL32UTF8 (UTF8 not recommended)
1. Latin characters -> 1 byte
2. Chinese characters(in BMP) -> 3 bytes
NLS_NCHAR_CHARACTERSET
Character encoding of NCHAR, NVARCHAR2 and NCLOB datatypes
eg: AL16UTF16 (UTF8 not recommended)
1. Latin characters -> 2 bytes
2. Chinese characters(in BMP) -> 2 bytes

Char

Store character data encoded by NLS_CHARACTERSET
Char(2000 byte)
We can store up to 666 Chinese characters(666 * 3 = 1998 bytes) and 2 Latin characters(2 * 1 = 2 bytes).
Char(n char)
We can store n chars as long as the length of encoded chars <= 2000 bytes
1. 0 < n <= 666
  We can store n(bytes = 3*n <= 1998) Chinese chars.
2. 666 < n <= 2000
  You can't store n(bytes = 3*n > 2000) Chinese chars.

VarChar2

Store character data encoded by NLS_CHARACTERSET
MAX_STRING_SIZE
1. STANDARD 4000 bytes
2. EXTENDED 32767 bytes
VarChar2(4000 byte)
We can store up to 1333 Chinese characters(1333 * 3 = 3999 bytes) and 1 Latin characters(1 * 1 = 1 bytes).
VarChar2(n char)
We can store n chars as long as the length of encoded chars <= 4000 bytes
1. 0 < n <= 1333
  We can store n(bytes = 3*n <= 3999) Chinese chars.
2. 1333 < n <= 4000
  You can't store n(bytes = 3*n > 2000) Chinese chars.

NChar

Store unicode character data encoded by NLS_NCHAR_CHARACTERSET

For a Unicode Standard-enabled database(NLS_CHARACTERSET is set to AL32UTF8), we can also use datatype char to store unicode character data. NChar is NOT the preferred option to store unicode character data.

NVarChar2

Store unicode character data encoded by NLS_NCHAR_CHARACTERSET
MAX_STRING_SIZE
1. STANDARD 4000 bytes
2. EXTENDED 32767 bytes

For a Unicode Standard-enabled database(NLS_CHARACTERSET is set to AL32UTF8), we can also use datatype VarChar2 to store unicode character data. NVarChar is NOT the preferred option to store unicode character data.

Internal Storage

We can use dump function to inspect how data is stored.

Sample output Typ=96 Len=5: 230,177,137,49,32
Typ=96 represent data type is Char
Len=5 represent data is stored by 5 bytes
'230,177,137,49,32' represent the actual data

DROP TABLE zz_char;

CREATE TABLE zz_char (
   char_b_1       CHAR(5 BYTE),
   varchar2_b_1   VARCHAR2(4000 BYTE),
   nchar_1        NCHAR(5),
   nvarchar2_1    NVARCHAR2(2000)
);

INSERT INTO zz_char (
   char_b_1,
   varchar2_b_1,
   nchar_1,
   nvarchar2_1
) VALUES (
   '汉1',
   '汉2',
   '字3',
   '字4'
);

SELECT char_b_1, dump(char_b_1),
       varchar2_b_1, dump(varchar2_b_1),
       nchar_1, dump(nchar_1),
       nvarchar2_1, dump(nvarchar2_1)
FROM zz_char;

Datatype	Characters	Encoding	Dump
char(5 byte)	汉1	AL32UTF8	Typ=96 Len=5: 230,177,137,49,32
varchar2(4000 byte)	汉2	AL32UTF8	Typ=1 Len=4: 230,177,137,50
nchar(5)	字3	AL16UTF16	Typ=96 Len=10: 91,87,0,51,0,32,0,32,0,32
nvarchar2(2000)	字4	AL16UTF16	Typ=1 Len=4: 91,87,0,52

汉1 -> AL32UTF8 (230,177,137,49,32)
230,177,137 -> 11100110 10110001 10001001 -> 11100110 10110001 10001001 -> 0110 1100 0100 1001 -> 0x 6C 49 -> 汉
49 -> character 1
32 -> blank character(blank-padded)
字3 -> AL16UTF16(91,87,0,51,0,32,0,32,0,32)
91,87 -> 0x 5B 57 -> 字
0,51 -> character 3
0,32,0,32,0,32 -> 3 blank characters(blank-padded)

Character Datatypes Summary

	Char	VarChar2	NChar	NVarChar2
Definition	char(n [byte\|char])	varchar2(n [byte\|char])	nchar(n)	nvarchar2(n)
Fixed-Variable	Fixed	Variable	Fixed	Variable
Length Semantics	byte(default) char	byte(default) char	char	char
Range in Bytes	1~2000	1~4000	1~2000	1~4000
Character Encoding	AL32UTF8	AL32UTF8	AL16UTF16	AL16UTF16
Maximum Latin Chars	2000	4000	1000	2000
Maximum Chinese Chars(BMP)	666 (2000/3)	1333 (4000/3)	1000	2000

Numeric Datatypes

Number Datatype

Number[(p[,s])]
p - Precision(total number of digits) (1~38)
s - Scale(number of digits to the right of decimal point) (-84~127)
1~21 bytes (see dump in Internal Numeric Format section)
Fixed-point Number(p,s)
Floating-point Number

N	Number(p,s)	Stored As
123.45	Number	123.45
123.45	Number(3)	123
123.45	Number(3,1)	exceeds precision
123.45	Number(3,-1)	120
123.45	Number(3,-2)	100
123.45	Number(3,-3)	0
123.45	Number(3,-4)	0
123.45	Number(5)	123
123.45	Number(5,1)	123.5
123.45	Number(5,2)	123.45
123.45	Number(5,3)	exceeds precision
0.012	Number(2,3)	0.012

Internal Storage

SELECT '9.9999999999999999999999999999999999999e125',
       dump(9.9999999999999999999999999999999999999E125),
       '1e-130',
       dump(1E-130),
       '-1e-130',
       dump(-1E-130),
       '-9.9999999999999999999999999999999999999e125',
       dump(-9.9999999999999999999999999999999999999E125),
       0,
       dump(0),
       utl_raw.cast_to_number('FF65'),
       dump(utl_raw.cast_to_number('FF65') ),
       utl_raw.cast_to_number('00'),
       dump(utl_raw.cast_to_number('00') )
FROM dual;

N	DUMP(N)	Description
9.99...9e125 (9 repeated 38 times)	Typ=2 Len=20: 255,100,...,100 (100 repeated 19 times)	Maximum Positive
1e-130	Typ=2 Len=2: 128,2	Minimum Positive
-1e-130	Typ=2 Len=3: 127,100,102	Maximum Negative
-9.99...9e125 (9 repeated 38 times)	Typ=2 Len=21: 0,2,...,2,102 (2 repeated 19 times)	Minimum Negative
0	Typ=2 Len=1: 128	Zero
utl_raw.cast_to_number('FF65')	Typ=2 Len=2: 255,101	Infinity
utl_raw.cast_to_number('00')	Typ=2 Len=1: 0	-Infinity

Positive Number 12345.6789
Typ=2 Len=6: 195,2,24,46,68,90
1. First byte 195 -> 1100 0011
  Sign -> positive, the first bit is 1
  Exponent -> 3, the following 7 bits (100 0011) - 64 (100 0000) = 3
2. The other data (2,24,46,68,90) subtract 1
  01, 23, 45, 67, 89
3. Get the result
  0.0123456789*100^3 = 12345.6789
Negative Number -12345.6789
Typ=2 Len=7: 60,100,78,56,34,12,102
1. First byte 60 -> 0011 1100
  Sign -> negative, the first bit is 0
  Exponent -> 3, the following 7 bits (011 1100) transfer to ones’ complement (100 0011) - 64 (100 0000) = 3
2. 100 subtract each of (100,78,56,34,12) then plus 1
  The last byte is 102 for every negative number (exclude it)
  01, 23, 45, 67, 89
  - Why 102? -2 > -2.0001 and 62,99,102 > 62,99,101,100,102
    
    Why 102?.png
3. Get the result
  -0.0123456789*100^3 = -12345.6789
Zero, Infinite, -Infinite

Float Datatype

Float[(p)]
p - binary precision (1-126)
binary precision * 0.30103 = decimal precision (digits = ceil(bits / log(2,10))

Float(n)	Float Value(1/3)	Number(n)	Number Value(1/3)
Float(1~3)	0.3	Number(1)	0.3
Float(4~6)	0.33	Number(2)	0.33
Float(126)	0.3...3(3 repeated 38 times)	Number(38)	0.3...3(3 repeated 38 times)

Binary_Float Datatype

Single-precision floating-point
5 bytes (4 data bytes + 1 length byte)

Internal Storage

IEEE754 Format wiki

wiki 4 bytes float - bits

wiki 4 byte float - result formula

Sign (-1) ^ b³¹ = (-1) ^ 0= (+1)
Exponent b₃₀...b₂₃ (0111 1100) = 124
(1.b₂₂...b₀)₂ = 1 + b₂₂ ^(-1) + b₂₁^(-2) + ... + b₀^(-23) = 1 + 1^(-2) = 1.25
Result = (+1) * 2 ^(124-127) * 1.25 = 0.15625

Oracle Format

select dump(0.15625f,16) from dual;
Typ=100 Len=4: be,20,0,0
Binary format 1011 1110 0010 0000 0000 0000 0000 0000

The first bit(sign bit) is different from IEEE754 format, all other bits are identical.

Binary_Double Datatype

Double-precision floating-point
9 bytes (8 data bytes + 1 length byte)

Internal Storage

IEEE754 Format wiki

wiki 8 bytes double - bits

wiki 8 bytes double - result formula

Numeric Datatypes Summary

Datatype	Precision	Value	Positive Range	Negative Range
Number	Decimal(0-9)	extract	1.0E-130 ~ 1.0E126(not inclusive)	-1.0E126(not inclusive) ~ -1.0E-130
Float	Binary(0-1)	extract	1.0E-130 ~ 1.0E126(not inclusive)	-1.0E126(not inclusive) ~ -1.0E-130
Binary_Float	Binary(0-1)	approximate	1.17549E-38F ~ 3.40282E+38F	-3.40282E+38F ~ -1.17549E-38F
Binary_Double	Binary(0-1)	approximate	2.22507485850720E-308 ~ 1.79769313486231E+308	-1.79769313486231E+308 ~ -2.22507485850720E-308

Date Datatypes

Alter date/timestamp/timestamp with tz format.
alter session set nls_date_format = 'yyyy-mm-dd hh24:mi:ss';
alter session set nls_timestamp_format = 'yyyy-mm-dd hh24:mi:ssxff';
alter session set nls_timestamp_tz_format = 'yyyy-mm-dd hh24:mi:ssxff tzr';

Datetime Datatypes

Date

Timestamp

Timestamp[(fractional_seconds_precision)]
fractional_seconds_precision (0-9, default 6)

Timestamp with time zone

TIMESTAMP [(fractional_seconds_precision)] WITH TIME ZONE
fractional_seconds_precision (0-9, default 6)

Timestamp with local time zone

TIMESTAMP [(fractional_seconds_precision)] WITH LOCAL TIME ZONE
fractional_seconds_precision (0-9, default 6)

Internal Storage and Summary

DROP TABLE zz_date;

CREATE TABLE zz_date (
   date_1        DATE,
   timestamp_1   TIMESTAMP(9),
   timestamp_2   TIMESTAMP(9) WITH TIME ZONE,
   timestamp_3   TIMESTAMP(9) WITH LOCAL TIME ZONE
);

INSERT INTO zz_date (
   date_1,
   timestamp_1,
   timestamp_2,
   timestamp_3
) VALUES (
   ( '2019-03-04 17:30:40' ),
   ( '2019-03-04 17:30:40.000000256' ),
   ( '2019-03-04 17:30:40.000000512 +08:00' ),
   ( '2019-03-04 17:30:40.000001024' )
);

SELECT date_1,
       dump(date_1),
       timestamp_1,
       dump(timestamp_1),
       timestamp_2,
       dump(timestamp_2),
       timestamp_3,
       dump(timestamp_3)
FROM zz_date;

	Date	Timestamp	Timestamp TZ	Timestamp LTZ
Value	2019-03-04 17:30:40	2019-03-04 17:30:40.000000256	2019-03-04 17:30:40.000000512 +08:00	2019-03-04 17:30:40.000001024
Dump	Typ=12 Len=7: 120,119,3,4,18,31,41	Typ=180 Len=11: 120,119,3,4,18,31,41,0,0,1,0	Typ=181 Len=13: 120,119,3,4,10,31,41,0,0,2,0,28,60	Typ=231 Len=11: 120,119,3,4,10,31,41,0,0,4,0
Length	7 bytes	11 bytes	13 bytes	11 bytes
Century	1st byte 120 20 = 120 - 100	<<	<<	<<
Year in century	2nd byte 119 19 = 119 - 100	<<	<<	<<
Month	3rd byte 3	<<	<<	<<
Day	4th byte 4	<<	<<	<<
Hour	5th byte 18 17 = 18 - 1	<<	<<	<<
Minute	6th byte 31 30 = 31 - 1	<<	<<	<<
Second	7th byte 41 40 = 41 - 1	<<	<<	<<
Nanosecond	-	8~11th bytes 0,0,1,0 256 = 0x 00 00 01 00	8~11th bytes 0,0,2,0 512 = 0x 00 00 02 00	8~11th bytes 0,0,4,0 1024 = 0x 00 00 04 00
Timezone hour	-	-	12th byte 28 8 = 28 - 20	-
Timezone minute	-	-	13th byte 60 0 = 60 - 60	-

Interval Datatypes

Interval year to month

INTERVAL YEAR [(year_precision)] TO MONTH
year_precision (0-9, default 2)

Interval day to second

INTERVAL DAY [(day_precision)] TO SECOND [(fractional_seconds_precision)]
day_precision (0-9, default 2)
fractional_seconds_precision (0-9, default 6)

Internal Storage and Summary

DROP TABLE zz_interval;

CREATE TABLE zz_interval (
   timestamp_1       TIMESTAMP(9),
   interval_year_1   INTERVAL YEAR(9) TO MONTH,
   interval_day_1    INTERVAL DAY(9) TO SECOND(9)
);

INSERT INTO zz_interval ( timestamp_1, interval_year_1, interval_day_1 ) VALUES (
   ( '2019-03-05 17:30:40.000000256' ),
   INTERVAL '+100-2' YEAR ( 9 ) TO MONTH,
   INTERVAL '10 1:2:3.000000001' DAY TO SECOND ( 9 )
);

INSERT INTO zz_interval ( timestamp_1, interval_year_1, interval_day_1 ) VALUES (
   ( '2019-03-05 17:30:40.000000256' ),
   to_yminterval('100-2'),
   to_dsinterval('10 1:2:3.000000001')
);

SELECT timestamp_1,
       timestamp_1 + interval_year_1,
       timestamp_1 + interval_day_1,
       dump(interval_year_1),
       dump(interval_day_1)
FROM zz_interval;

	Interval year to month	Interval day to second
Literal value	INTERVAL '+100-2' YEAR ( 9 ) TO MONTH	INTERVAL '10 1:2:3.000000001' DAY TO SECOND ( 9 )
To_interval value	to_yminterval('100-2')	to_dsinterval('10 1:2:3.000000001')
Dump	Typ=182 Len=5: 128,0,0,100,62	Typ=183 Len=11: 128,0,0,10,61,62,63,128,0,0,1
Length	5 bytes	11 bytes
Description	A interval of 100 years and 2 months	A interval of 10d,1h,2m,3s and 1 nanosecond
Year	1~4th bytes 128,0,0,100 100 = 0x(80 00 00 64) - 0x(80 00 00 00)	-
Month	5th byte 62 2 = 62 - 60	-
Day	-	1~4th bytes 128,0,0,10 10 = 0x(80 00 00 0A) - 0x(80 00 00 00)
Hour	-	5th byte 61 1 = 61 - 60
Minute	-	6th byte 62 2 = 62 - 60
Second	-	7th byte 63 3 = 63 - 60
Nanosecond	-	8~11th bytes 128,0,0,1 1 = 0x(80 00 00 01) - 0x(80 00 00 00)

LOB Datatypes

Create file /tmp/abc.txt in database server file system
sh-4.2# echo 123456 > /tmp/abc.txt
Create oracle directory object
CREATE DIRECTORY TMP_DIR AS '/tmp';
Create lob table

CREATE TABLE zz_lob (
   lob_id    NUMBER,
   clob_1    CLOB,
   nclob_1   NCLOB,
   blob_1    BLOB,
   bfile_1   BFILE
);

CLOB

Store large object data of characters encoded by NLS_CHARACTERSET
Maximum size is (4 gigabytes - 1) * (database block size)

INSERT INTO zz_lob ( clob_1 ) VALUES (to_clob('123'));

NCLOB

Store large object data of unicode character encoded by NLS_NCHAR_CHARACTERSET
Maximum size is (4 gigabytes - 1) * (database block size)

INSERT INTO zz_lob ( nclob_1 ) VALUES (to_nclob('123'));

BLOB

Store binary large object(image, video, audio..)
Maximum size is (4 gigabytes - 1) * (database block size)

Store BLOB

DECLARE
   src_lob    BFILE := bfilename('TMP_DIR', 'abc.txt');
   dest_lob   BLOB;
BEGIN
   INSERT INTO zz_lob ( lob_id, blob_1 ) VALUES ( 2, empty_blob() ) RETURNING blob_1 INTO dest_lob;
   dbms_lob.open(src_lob, dbms_lob.lob_readonly);
   dbms_lob.loadfromfile(
      dest_lob   => dest_lob,
      src_lob    => src_lob,
      amount     => dbms_lob.getlength(src_lob)
   );
   dbms_lob.close(src_lob);
   COMMIT;
END;

BFILE

Store a BFILE locator which points to a binary file in file system outside the database
The BFILE locator (directory name and file name)
Maximum size of BFILE is 4 gigabytes

Store BFILE

bfilename

INSERT INTO zz_lob ( lob_id, bfile_1 ) VALUES (
   1,
   bfilename('TMP_DIR', 'abc.txt')
);

Read BFILE by dbms_lob api

DECLARE
   fil   BFILE;
   pos   NUMBER := 1;
   bat   NUMBER := 5;
   buf   RAW(5);
BEGIN
   SELECT bfile_1 INTO fil FROM zz_lob WHERE lob_id = 1;
--   fil:=BFILENAME('TMP_DIR','abc.txt');

   dbms_lob.open(fil, dbms_lob.lob_readonly);

   FOR i IN 1..ceil(dbms_lob.getlength(fil) / bat) LOOP
      pos   := 1 + bat * ( i - 1 );
      dbms_output.put_line('i ' ||  i || ' start ' || pos || ' end ' || (pos + bat) );
      dbms_lob.read(fil, bat, pos, buf);
      dbms_output.put_line(utl_raw.cast_to_varchar2(buf) );
   END LOOP;
   dbms_lob.close(fil);
END;

BFILE output

--i 1 start 1 end 6
12345
--i 2 start 6 end 11
6

Other Datatypes

Raw

Raw(n)
Store binary data/byte string
Variable length
MAX_STRING_SIZE
1. STANDARD 2000 bytes
2. EXTENDED 32767 bytes

DROP TABLE zz_raw;

CREATE TABLE zz_raw (
   raw_1   RAW(5),
   raw_2   RAW(5)
);

DELETE FROM zz_raw;

INSERT INTO zz_raw VALUES (
   utl_raw.cast_to_raw('a'),
   utl_raw.cast_from_number(1)
);

SELECT raw_1,
       dump(raw_1, 16),
       utl_raw.cast_to_varchar2(raw_1),
       raw_2,
       dump(raw_2, 16),
       utl_raw.cast_to_number(raw_2)
FROM zz_raw;

Raw	Dump(Raw,16)	value
utl_raw.cast_to_raw('a') 0x61	Typ=23 Len=1: 61	utl_raw.cast_to_varchar2 = a
utl_raw.cast_from_number(1) 0xC102	Typ=23 Len=2: c1,2	utl_raw.cast_to_number = 1

RowId URowId

RowId

Base64 string representing unique physical address of each row in heap-organized table.

RowId Type
RowId type: 0 is restricted, 1 is extended
dbms_rowid.rowid_type(ROWID)
Data Object Number
The unique indentifier of the object.
dbms_rowid.rowid_object(ROWID)
File Number
The relative number of the datafile in the tablespace.
dbms_rowid.rowid_relative_fno(ROWID)
Data Block Number
The relative block number in the datafile.
dbms_rowid.rowid_block_number(ROWID)
Row Number
The relative rownum within the block.
dbms_rowid.rowid_row_number(ROWID)

URowId

Base 64 string representing the logical address of a row of an index-organized table.

UROWID [(size)]
size (4000bytes)

Reference

Oracle Datatypes

Fixed-point and floating-point representations of numbers
Introduction to Fixed Point Number Representation

How numbers are saved in oracle
Oracle dump number

Single-precision_floating-point
Double-precision_floating-point_format

ORAFAQ Data_types

Oracle Datatypes

Character Datatypes

Char

VarChar2

NChar

NVarChar2

Internal Storage

Character Datatypes Summary

Numeric Datatypes

Number Datatype

Internal Storage

Float Datatype

Binary_Float Datatype

Internal Storage

IEEE754 Format wiki

Oracle Format

Binary_Double Datatype

Internal Storage

IEEE754 Format wiki

Numeric Datatypes Summary

Date Datatypes

Datetime Datatypes

Date

Timestamp

Timestamp with time zone

Timestamp with local time zone

Internal Storage and Summary

Interval Datatypes

Interval year to month

Interval day to second

Internal Storage and Summary

LOB Datatypes

CLOB

NCLOB

BLOB

Store BLOB

BFILE

Store BFILE

Other Datatypes

Raw

RowId URowId

RowId

URowId

Reference

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