DECIMAL Data Type (Impala 3.0 or higher only)
DECIMAL data type is a numeric data type with fixed scale and
The data type is useful for storing and doing operations on precise decimal values.
precision represents the total number of digits that can be represented regardless of the location of the decimal point.
This value must be between 1 and 38, specified as an integer literal.
The default precision is 9.
scale represents the number of fractional digits.
This value must be less than or equal to the precision, specified as an integer literal.
The default scale is 0.
When the precision and the scale are omitted, a
DECIMAL is treated as
The range of
DECIMAL type is -10^38 +1 through 10^38 –1.
The largest value is represented by
The most precise fractional value (between 0 and 1, or 0 and -1) is represented by
DECIMAL(38, 38), with 38 digits to the right of the decimal point. The
value closest to 0 would be .0000...1 (37 zeros and the final 1). The value closest to 1
would be .999... (9 repeated 38 times).
Memory and disk storage:
Only the precision determines the storage size for
DECIMAL values, and
the scale setting has no effect on the storage size. The following table describes the
in-memory storage once the values are loaded into memory.
|1 - 9||4 bytes|
|10 - 18||8 bytes|
|19 - 38||16 bytes|
The on-disk representation varies depending on the file format of the table.
Text, RCFile, and SequenceFile tables use ASCII-based formats as below:
- Leading zeros are not stored.
- Trailing zeros are stored.
DECIMALvalue takes up as many bytes as the precision of the value, plus:
- One extra byte if the decimal point is present.
- One extra byte for negative values.
Parquet and Avro tables use binary formats and offer more compact storage for
DECIMAL values. In these tables, Impala stores each value in fewer bytes
where possible depending on the precision specified for the
column. To conserve space in large tables, use the smallest-precision
Precision and scale in arithmetic operations:
For all arithmetic operations, the resulting precision is at most 38.
If the resulting precision would be greater than 38, Impala truncates the result from the back, but keeps at least 6 fractional digits in scale and rounds.
DECIMAL(38, 20) * DECIMAL(38, 20) returns
DECIMAL(38, 6). According to the table below, the resulting precision and
scale would be
(77, 40), but they are higher than the maximum precision
and scale for
DECIMAL. So, Impala sets the precision to the maximum
allowed 38, and truncates the scale to 6.
DECIMALvalues in arithmetic operations, the precision and scale of the result value are determined as follows. For better readability, the following terms are used in the table below:
P1, P2: Input precisions
S1, S2: Input scales
L1, L2: Leading digits in input
DECIMALs, i.e., L1 = P1 - S1 and L2 = P2 - S2
|Operation||Resulting Precision||Resulting Scale|
|Addition and Subtraction||
max (L1, L2) + max (S1, S2) + 1
1 is for carry-over.
|max (S1, S2)|
|Multiplication||P1 + P2 + 1||S1 + S2|
|Division||L1 + S2 + max (S1 + P2 + 1, 6)||max (S1 + P2 + 1, 6)|
|Modulo||min (L1, L2) + max (S1, S2)||max (S1, S2)|
Precision and scale in functions:
DECIMALvalues in built-in functions, the precision and scale of the result value are determined as follows:
The result of the
SUMaggregate function on a
Scale: The same scale as the input column
The result of
AVGaggregate function on a
Scale: max(Scale of input column, 6)
Implicit conversions in DECIMAL assignments:
Impala enforces strict conversion rules in decimal assignments like in
UNION statements, or in functions like
If there is not enough precision and scale in the destination, Impala fails with an error.
DECIMALand other numeric types as below:
DECIMALis implicitly converted to
FLOATwhen necessary even with a loss of precision. It can be necessary, for example when inserting a
DECIMALvalue into a
DOUBLEcolumn. For example:
CREATE TABLE flt(c FLOAT); INSERT INTO flt SELECT CAST(1e37 AS DECIMAL(38, 0)); SELECT CAST(c AS DECIMAL(38, 0)) FROM flt; Result: 9999999933815812510711506376257961984
The result has a loss of information due to implicit casting. This is why we discourage using the
FLOATtypes in general.
FLOATcannot be implicitly converted to
DECIMAL. An error is returned.
DECIMALis implicitly converted to
DECIMALif all digits fit in the resulting
DECIMAL.For example, the following query returns an error because the resulting type that guarantees that all digits fit cannot be determined .
SELECT GREATEST (CAST(1 AS DECIMAL(38, 0)), CAST(2 AS DECIMAL(38, 37)));
Integer values can be implicitly converted to
DECIMALwhen there is enough room in the
DECIMALto guarantee that all digits fit. The integer types require the following numbers of digits to the left of the decimal point when converted to
BIGINT: 19 digits
INT: 10 digits
SMALLINT: 5 digits
TINYINT: 3 digits
CREATE TABLE decimals_10_8 (x DECIMAL(10, 8)); INSERT INTO decimals_10_8 VALUES (CAST(1 AS TINYINT));
INSERTstatement fails because
TINYINTrequires room for 3 digits to the left of the decimal point in the
CREATE TABLE decimals_11_8(x DECIMAL(11, 8)); INSERT INTO decimals_11_8 VALUES (CAST(1 AS TINYINT));
INSERTstatement succeeds because there is enough room for 3 digits to the left of the decimal point that
UNION, the resulting precision and scales are determined as follows.
Precision: max (L1, L2) + max (S1, S2)
If the resulting type does not fit in the
DECIMALtype, an error is returned. See the first example below.
- Scale: max (S1, S2)
DECIMAL(20, 0) UNION DECIMAL(20, 20)would require a
DECIMAL(40, 20)to fit all the digits. Since this is larger than the max precision for
DECIMAL, Impala returns an error. One way to fix the error is to cast both operands to the desired type, for example
DECIMAL(20, 2) UNION DECIMAL(8, 6)returns
INT UNION DECIMAL(9, 4)returns
INThas the precision 10 and the scale 0, so it is treated as
DECIMAL(10, 0) UNION DECIMAL(9. 4).
Casting between DECIMAL and other data types:
CASTto explicitly convert between
DECIMALand other types in decimal assignments like in
UNIONstatements, or in functions like
You can cast the following types to
You can cast
DECIMALto the following types:
DECIMALand other numeric types as below:
Precision: If you cast a value with bigger precision than the precision of the destination type, Impala returns an error. For example,
CAST(123456 AS DECIMAL(3,0))returns an error because all digits do not fit into
Scale: If you cast a value with more fractional digits than the scale of the destination type, the fractional digits are rounded. For example,
CAST(1.239 AS DECIMAL(3, 2))returns
Casting STRING to DECIMAL:
STRINGof numeric characters in columns, literals, or expressions to
DECIMALas long as number fits within the specified target
DECIMALtype without overflow.
If scale in
STRING> scale in
DECIMAL, the fractional digits are rounded to the
CAST('98.678912' AS DECIMAL(15, 1))returns
If # leading digits in
STRING> # leading digits in
DECIMAL, an error is returned.
CAST('123.45' AS DECIMAL(2, 2))returns an error.
Exponential notation is supported when casting from
CAST('1.0e6' AS DECIMAL(32, 0)) returns
Casting any non-numeric value, such as
'ABC' to the
DECIMAL type returns an error.
Casting DECIMAL to TIMESTAMP:
DECIMAL value N to
TIMESTAMP produces a value
that is N seconds past the start of the epoch date (January 1, 1970).
DECIMAL vs FLOAT consideration:
DOUBLE types can cause problems or
unexpected behavior due to inability to precisely represent certain fractional values, for
example dollar and cents values for currency. You might find output values slightly
different than you inserted, equality tests that do not match precisely, or unexpected
GROUP BY columns. The
DECIMAL type can help
reduce unexpected behavior and rounding errors, but at the expense of some performance
overhead for assignments and comparisons.
Literals and expressions:
Numeric literals without a decimal point
The literals are treated as the smallest integer that would fit the literal. For
Large literals that do not fit into any integer type are treated as
The literals too large to fit into a
DECIMAL(38, 0)are treated as
- The literals are treated as the smallest integer that would fit the literal. For example,
Numeric literals with a decimal point
The literal with less than 38 digits are treated as
The literals with 38 or more digits are treated as a
- The literal with less than 38 digits are treated as
Exponential notation is supported in
To represent a very large or precise
DECIMALvalue as a literal, for example one that contains more digits than can be represented by a
BIGINTliteral, use a quoted string or a floating-point value for the number and
CASTthe string to the desired
CAST('999999999999999999999999999999' AS DECIMAL(38, 5)))
File format considerations:
DECIMALdata type can be stored in any of the file formats supported by Impala.
Impala can query Avro, RCFile, or SequenceFile tables that contain
DECIMALcolumns, created by other Hadoop components.
Impala can query and insert into Kudu tables that contain
DECIMALdata type is fully compatible with HBase tables.
DECIMALdata type is fully compatible with Parquet tables.
Values of the
DECIMALdata type are potentially larger in text tables than in tables using Parquet or other binary formats.
When writing a C++ UDF, use the
DecimalVal data type defined in
Changing precision and scale:
ALTER TABLE ... REPLACE COLUMNSstatement to change the precision and scale of an existing
For text-based formats (text, RCFile, and SequenceFile tables)
If the values in the column fit within the new precision and scale, they are returned correctly by a query.
If any values that do not fit within the new precision and scale:
Impala returns an error if the query option
ABORT_ON_ERRORis set to
Impala returns a
NULLand warning that conversion failed if the query option
ABORT_ON_ERRORis set to
- Impala returns an error if the query option
Leading zeros do not count against the precision value, but trailing zeros after the decimal point do.
For binary formats (Parquet and Avro tables)
ALTER TABLE ... REPLACE COLUMNSstatement that changes the precision or scale of a
DECIMALcolumn succeeds, any subsequent attempt to query the changed column results in a fatal error. This is because the metadata about the columns is stored in the data files themselves, and
ALTER TABLEdoes not actually make any updates to the data files. The other unaltered columns can still be queried successfully.
If the metadata in the data files disagrees with the metadata in the metastore database, Impala cancels the query.
DECIMAL column as a partition key provides you a better match
between the partition key values and the HDFS directory names than using a
FLOAT partitioning column.
Column statistics considerations:
DECIMAL type has a fixed size, the maximum and average size
fields are always filled in for column statistics, even before you run the
Compatibility with older version of DECIMAL:
This version of
DECIMAL type is the default in
Impala 3.0 and higher. The key differences between this
DECIMAL and the previous
DECIMAL V1 in Impala
2.x include the following.
|DECIMAL in Impala 3.0 or higher||DECIMAL in Impala 2.12 or lower|
|Overall behavior||Returns either the result or an error.||Returns either the result or
|Overflow behavior||Aborts with an error.||Issues a warning and returns
|Truncation / rounding behavior in arithmetic||Truncates and rounds digits from the back.||Truncates digits from the front.|
|String cast||Truncates from the back and rounds.||Truncates from the back.|
DECIMALtype for the backward compatibility of your queries, set the
DECIMAL_V2query option to
Compatibility with other databases:
DECIMAL data type in Impala for applications where you used the
NUMBER data type in Oracle.
DECIMAL type does not support the Oracle idioms of
* for scale.
DECIMAL type does not support negative values for precision.