Data Type Mappings

The driver maps types from the data source to the corresponding data type available in the schema. The table below documents these mappings.

Note that the NUMERIC type supports 38 digits of precision and the BIGDECIMAL type supports 76 digits of precision. Most platforms do not have a decimal type that supports the full precision of these values (.NET decimal supports 28 digits, and Java BigDecimal supports 38 by default). If this is the case then these columns can be cast to a string when queried, or the connection can be configured to ignore them by setting IgnoreTypes=decimal.

STRUCT and ARRAY Types

Google BigQuery supports two kinds of types for storing compound values in a single row, STRUCT and ARRAY. In some places within Google BigQuery these are also known as RECORD and REPEATED types.

A STRUCT is a fixed-size group of values which are accessed by name and can have different types. The driver flattens structs so their individual fields can be accessed using dotted names. Note that these dotted names must be quoted.

-- trade_value STRUCT<currency STRING, value FLOAT>
SELECT CONCAT([trade_value.value], ' ', NULLIF([trade_value.currency], 'USD'))
FROM trades

An ARRAY is a group of values with the same type that can have any size. The driver treats the array as a single compound value and reports it as a JSON aggregate.

These types may be combined such that a STRUCT type contains an ARRAY field, or an ARRAY field is a list of STRUCT values. The outer type takes precedence in how the field is processed:

/* Table contains fields: 
  stocks STRUCT<symbol STRING, prices ARRAY<FLOAT>>
  offers: ARRAY<STRUCT<currency STRING, value FLOAT>> 
*/

SELECT [stocks.symbol], /* ARRAY field can be read from STRUCT, but is converted to JSON */
       [stocks.prices], 
       [offers]         /* STRUCT fields in an ARRAY cannot be accessed */
FROM market

Type Parameters

The driver exposes parameters on the following types. In each case the type parameters are optional, Google BigQuery has default values for types that are not parameterized.

• STRING(length)
• BYTES(length)
• NUMERIC(precision) or NUMERIC(precision, scale)
• BIGNUMERIC(precision) or BIGNUMERIC(precision, scale)

These parameters are primarily for restricting the data written to the table. They are included in the table metadata as the column size for STRING and BYTES, and the numeric precision and scale for NUMERIC and BIGNUMERIC.

Type parameters have no effect on queries and are not reported within query metadata. For example, here the output of CONCAT is a plain STRING even though its inputs are a STRING(100) and b STRING(100).

SELECT CONCAT(a, b) FROM table_with_length_params