Supported Data Types

In the big data field, the mainstream file format is ORC, which is supported by GaussDB(DWS). You can use Hive to export data to an ORC file and use a read-only foreign table to query and analyze the data in the ORC file. Therefore, you need to map the data types supported by the ORC file format with the data types supported by GaussDB(DWS). For details, see Table 1. Similarly, GaussDB(DWS) exports data through a write-only foreign table, and stores the data in the ORC format. Using Hive to read the ORC file content also requires matched data types. Table 2 shows the matching relationship.

**Table 1** Mapping between ORC read-only foreign tables and Hive data types
Type	Type Supported by GaussDB(DWS) Foreign Tables	Hive Table Type
1-byte integer	TINYINT (not recommended)	TINYINT
1-byte integer	SMALLINT (recommended)	TINYINT
2-byte integer	SMALLINT	SMALLINT
4-byte integer	INTEGER	INT
8-byte integer	BIGINT	BIGINT
Single-precision floating point number	FLOAT4 (REAL)	FLOAT
Double-precision floating point number	FLOAT8(DOUBLE PRECISION)	DOUBLE
Scientific data type	DECIMAL[p (,s)] (The maximum precision can reach up to 38.)	DECIMAL (The maximum precision can reach up to 38.) (HIVE 0.11)
Date type	DATE	DATE
Time type	TIMESTAMP	TIMESTAMP
Boolean type	BOOLEAN	BOOLEAN
CHAR type	CHAR(n)	CHAR (n)
VARCHAR type	VARCHAR(n)	VARCHAR (n)
String (large text object)	TEXT(CLOB)	STRING

**Table 2** Mapping between ORC write-only foreign tables and Hive data types
Type	Type Supported by GaussDB(DWS) Internal Tables (Data Source Table)	Type Supported by GaussDB(DWS) Write-only Foreign Tables	Hive Table Type
1-byte integer	TINYINT	TINYINT (not recommended)	SMALLINT
1-byte integer	TINYINT	SMALLINT (recommended)	SMALLINT
2-byte integer	SMALLINT	SMALLINT	SMALLINT
4-byte integer	INTEGER, BINARY_INTEGER	INTEGER	INT
8-byte integer	BIGINT	BIGINT	BIGINT
Single-precision floating point number	FLOAT4, REAL	FLOAT4, REAL	FLOAT
Double-precision floating point number	DOUBLE PRECISION, FLOAT8, BINARY_DOUBLE	DOUBLE PRECISION, FLOAT8, BINARY_DOUBLE	DOUBLE
Scientific data type	DECIMAL, NUMERIC	DECIMAL[p (,s)] (The maximum precision can reach up to 38.)	precision ≤ 38: DECIMAL; precision > 38: STRING
Date type	DATE	TIMESTAMP[(p)] [WITHOUT TIME ZONE]	TIMESTAMP
Time type	TIME [(p)] [WITHOUT TIME ZONE], TIME [(p)] [WITH TIME ZONE]	TEXT	STRING
	TIMESTAMP[(p)] [WITHOUT TIME ZONE], TIMESTAMP[(p)][WITH TIME ZONE], SMALLDATETIME	TIMESTAMP[(p)] [WITHOUT TIME ZONE]	TIMESTAMP
	INTERVAL DAY (l) TO SECOND (p), INTERVAL [FIELDS] [(p)]	VARCHAR(n)	VARCHAR(n)
Boolean type	BOOLEAN	BOOLEAN	BOOLEAN
CHAR type	CHAR(n), CHARACTER(n), NCHAR(n)	CHAR(n), CHARACTER(n), NCHAR(n)	n ≤ 255: CHAR(n); n > 255: STRING
VARCHAR type	VARCHAR(n), CHARACTER VARYING(n), VARCHAR2(n)	VARCHAR(n)	n ≤ 65535: VARCHAR(n); n > 65535: STRING
VARCHAR type	NVARCHAR2(n)	TEXT	STRING
String (large text object)	TEXT, CLOB	TEXT, CLOB	STRING
Monetary type	MONEY	NUMERIC	BIGINT

The GaussDB(DWS) foreign table supports the NULL definition, and the Hive data table supports and uses the corresponding NULL definition.
The value range of TINYINT in the Hive data table is [-128, 127], and the value range of TINYINT in GaussDB(DWS) is [0, 255]. You are advised to use the SMALLINT type when creating the GaussDB(DWS) read-only foreign table for TINYINT in the Hive table. If TINYINT is used, the read value may be different from the actual value. Similarly, when exporting data of the TINYINT type from GaussDB(DWS), you are advised to use the SMALLINT type for write-only foreign tables and Hive tables.
The time zone definition is not supported by the date and time types of the GaussDB(DWS) foreign table, or by the Hive table.
The date type in Hive contains only date. The date type in GaussDB(DWS) contains date and time.
In GaussDB(DWS), ORC files can be compressed in ZLIB, SNAPPY, LZ4, or NONE mode.
The FLOAT4 format itself is not accurate, and the sum operation results vary with environments. You are advised to use the DECIMAL type in high-precision scenarios.
In Teradata-compatible mode, foreign tables do not support the DATE type.