Floating-point types
Floating-point types are fixed-length, non-precise numeric types. The value range and precision depend on the type length, precision, and scale, and whether the type is unsigned.
Precision and scale represent the maximum number of significant digits in decimal and the maximum number of significant digits in the fractional part, respectively. The maximum number of significant digits in the integer part is equal to the precision minus the scale. The maximum value of precision is 255 (scale can only be 0), and the maximum value of scale is 30.
The precision of floating-point types is only the theoretical value specified by the IEEE standard. In practice, it may vary slightly due to hardware or operating system limitations.
The following table shows the storage length and value range of floating-point types when precision and scale are not specified.
| Type | Length (bytes) | Value range | Precision |
|---|---|---|---|
FLOAT | 4 | [-3.402823466E+38, -1.175494351E-38], 0, and [1.175494351E-38,3.402823466E+38] | 7 digits |
DOUBLE | 8 | [-1.7976931348623157E+308, -2.2250738585072014E-308], 0, and [2.2250738585072014E-308,1.7976931348623157E+308] | 15 digits |
If precision and scale are specified, the value range is determined in the same way as for fixed-point types.
FLOAT
FLOAT is used to represent a small (single-precision) floating-point number. The syntax is as follows:
FLOAT[(M,D)] [UNSIGNED] [ZEROFILL]
M is the total number of digits that can be stored, and D is the number of digits after the decimal point. If M and D are omitted, the value is stored within the hardware's allowed limits. Single-precision floating-point numbers are accurate to about 7 decimal places.
If you specify ZEROFILL for a numeric column, seekdb automatically adds the UNSIGNED attribute to the column. If UNSIGNED is specified, negative values are not allowed.
FLOAT(M,D) is an outdated syntax and is not recommended for use.
FLOAT also supports the following syntax:
FLOAT(p) [UNSIGNED] [ZEROFILL]
p represents the precision in bits, but it is only used to determine whether the result data type is FLOAT or DOUBLE. If p is between 0 and 24, the data type becomes FLOAT without M or D values. If p is between 25 and 53, the data type becomes DOUBLE without M or D values. The value range of the result column is the same as that of the single-precision FLOAT or double-precision DOUBLE data types described earlier.
DOUBLE
DOUBLE is used to represent a normal-sized (double-precision) floating-point number. The syntax is as follows:
DOUBLE[(M,D)] [UNSIGNED] [ZEROFILL]
M is the total number of digits that can be stored, and D is the number of digits after the decimal point. If M and D are omitted, the value is stored within the hardware's allowed limits. Double-precision floating-point numbers are accurate to about 15 decimal places.
If you specify ZEROFILL for a numeric column, seekdb automatically adds the UNSIGNED attribute to the column. If UNSIGNED is specified, negative values are not allowed.
DOUBLE[(M,D)] is an outdated syntax from MySQL and is not recommended for use. If you need precise queries, it is recommended to use the DECIMAL type.
DOUBLE PRECISION
DOUBLE PRECISION is a synonym for DOUBLE. The syntax is as follows:
DOUBLE PRECISION[(M,D)] [UNSIGNED] [ZEROFILL], REAL[(M,D)] [UNSIGNED] [ZEROFILL]
Binary floating-point numbers do not currently support special values such as infinity and NaN.