Data Type

Note:

1. SYMBOL is a special STRING type.
2. ANY DICTIONARY is the data type in DolphinDB for JSON.
3. COMPRESS can only be generated with function compress .
4. The DURATION type can be generated with function duration or by combining an integer with a unit of time (case sensitive): y, M, w, d, B, H, m, s, ms, us, ns. The range of a DURATION value is -2 ³¹ +1~2 ³¹ -1. If a data type overflow occurs, the data is treated as NULL value.
5. DolphinDB uses IEEE 754 standard for the data types DOUBLE and FLOAT. If a data type overflow occurs, the data is treated as NULL value.
6. Only in-memory tables or DFS tables in TSDB databases support BLOB types.
7. The character "S" of DECIMAL32(S), DECIMAL64(S) and DECIMAL128(S) means scale, which determines how many decimal digits a fraction can have. The value range of S for DECIMAL32(S) is [0,9], for DECIMAL64(S) is [0,18], for DECIMAL128(S) is [0,38]. DECIMAL32 is stored as the int32_t type and takes 4 bytes; DECIMAL64 is stored as the int64_t type and takes 8 bytes; DECIMAL128 is stored as the int128_t type and takes 16 bytes. DECIMAL(0) can represent integers in the range of [-999,999,999, 999,999,999], while the 4-byte integer (INT32) is in the range of [-2,147,483,648, 2,147,483,647]. Therefore, if the integral range of a numeric value exceeds the valid range of DECIMAL32 but is within the range of [-2147483648, 2147483647], it can still be converted to DECIMAL 32. However, when converting a string to DECIMAL32, if its length exceeds the range, the system raises an exception.

decimal32(1000000000, 0)
            // output
            1000000000
            
            decimal32(`1000000000, 0)
            // output
            Convert string to DECIMAL failed: Decimal math overflow

Type check

typestr 3l;
// output
LONG

type 3l;
// output
5

x=3;
if(type(x) == INT){y=10};
y;

// output
10

Data Range

x=-128c;
x;
// output
00c
typestr x;
// output
CHAR

Data type symbols

A data type symbol is used for declaring a data type of a constant. In the example below, without specifying a data type symbol, number 3 is stored in memory by default as an integer. If you would like to save it as a floating number, it should be declared as 3f(float) or 3F(double).

typestr 3;
// output
INT

typestr 3f;
// output
FLOAT

typestr 3F;
// output
DOUBLE

typestr 3l;
// output
LONG

typestr 3h;
// output
SHORT

typestr 3c;
// output
CHAR

typestr 3b;
// output
BOOL

typestr 3P;   // New in version 2.00.9.4
// output
DECIMAL64

Symbol and String

In some circumstances it might be optimal to save strings as SYMBOL types in DolphinDB. SYMBOL types are stored as integers in DolphinDB to allow more efficient sorting and comparison. Therefore, SYMBOL types could potentially improve operating performance and save storage space. On the other hand, mapping strings to integers (hashing) takes time and the hash table consumes memory.

The following rules could help you decide whether to use SYMBOL types or not:

Symbol vector creation

syms=array(SYMBOL, 0, 100);
// create an empty symbol array;

typestr syms;
// output
FAST SYMBOL VECTOR
syms.append!(`IBM`C`MS);
syms;
// output
["IBM","C","MS"]

syms=`IBM`C`MS;
typestr syms;
// output
STRING VECTOR

// converting to a symbol vector;
sym=syms$SYMBOL;

typestr sym;
// output
FAST SYMBOL VECTOR
typestr syms;
// output
STRING VECTOR

syms=`IBM`C`MS;
symRand=rand(syms, 10);
//generate a random SYMBOL vector

symRand;
// output
["IBM","IBM","IBM","MS","C","C","MS","IBM","C","MS"]
typestr symRand;
// output
FAST SYMBOL VECTOR