Conversion rules (original) (raw)
GoogleSQL for BigQuery supports conversion. Conversion includes, but isn't limited to, casting, coercion, and supertyping.
- Casting is explicit conversion and uses theCAST() function.
- Coercion is implicit conversion, which GoogleSQL performs automatically under the conditions described below.
- A supertype is a common type to which two or more expressions can be coerced.
There are also conversions that have their own function names, such asPARSE_DATE(). To learn more about these functions, seeConversion functions.
Comparison of casting and coercion
The following table summarizes all possible cast and coercion possibilities for GoogleSQL data types. The Coerce to column applies to all expressions of a given data type, (for example, a column), but literals and parameters can also be coerced. Seeliteral coercion andparameter coercion for details.
| From type | Cast to | Coerce to |
|---|---|---|
| INT64 | BOOLINT64NUMERICBIGNUMERICFLOAT64STRING | NUMERICBIGNUMERICFLOAT64 |
| NUMERIC | INT64NUMERICBIGNUMERICFLOAT64STRING | BIGNUMERICFLOAT64 |
| BIGNUMERIC | INT64NUMERICBIGNUMERICFLOAT64STRING | FLOAT64 |
| FLOAT64 | INT64NUMERICBIGNUMERICFLOAT64STRING | |
| BOOL | BOOLINT64STRING | |
| STRING | BOOLINT64NUMERICBIGNUMERICFLOAT64STRINGBYTESDATEDATETIMETIMETIMESTAMPRANGE | |
| BYTES | STRINGBYTES | |
| DATE | STRINGDATEDATETIMETIMESTAMP | DATETIME |
| DATETIME | STRINGDATEDATETIMETIMETIMESTAMP | |
| TIME | STRINGTIME | |
| TIMESTAMP | STRINGDATEDATETIMETIMETIMESTAMP | |
| ARRAY | ARRAY | |
| STRUCT | STRUCT | |
| RANGE | RANGESTRING |
Casting
Most data types can be cast from one type to another with the CAST function. When using CAST, a query can fail if GoogleSQL is unable to perform the cast. If you want to protect your queries from these types of errors, you can use SAFE_CAST. To learn more about the rules for CAST, SAFE_CAST and other casting functions, seeConversion functions.
Coercion
GoogleSQL coerces the result type of an argument expression to another type if needed to match function signatures. For example, if function func()is defined to take a single argument of type FLOAT64and an expression is used as an argument that has a result type ofINT64, then the result of the expression will be coerced to FLOAT64 type before func() is computed.
Literal coercion
GoogleSQL supports the following literal coercions:
| Input data type | Result data type | Notes |
|---|---|---|
| FLOAT64 literal | NUMERIC | Coercion may not be exact, and returns a close value. |
| STRING literal | DATEDATETIMETIMETIMESTAMP |
Literal coercion is needed when the actual literal type is different from the type expected by the function in question. For example, if function func() takes a DATE argument, then the expression func("2014-09-27") is valid because the string literal "2014-09-27" is coerced toDATE.
Literal conversion is evaluated at analysis time, and gives an error if the input literal can't be converted successfully to the target type.
Parameter coercion
GoogleSQL supports the following parameter coercions:
| Input data type | Result data type |
|---|---|
| STRING parameter | DATEDATETIMETIMETIMESTAMP |
If the parameter value can't be coerced successfully to the target type, an error is provided.
Supertypes
A supertype is a common type to which two or more expressions can be coerced. Supertypes are used with set operations such as UNION ALL and expressions such as CASE that expect multiple arguments with matching types. Each type has one or more supertypes, including itself, which defines its set of supertypes.
| Input type | Supertypes |
|---|---|
| BOOL | BOOL |
| INT64 | INT64FLOAT64NUMERICBIGNUMERIC |
| FLOAT64 | FLOAT64 |
| NUMERIC | NUMERICBIGNUMERICFLOAT64 |
| DECIMAL | DECIMALBIGDECIMALFLOAT64 |
| BIGNUMERIC | BIGNUMERICFLOAT64 |
| BIGDECIMAL | BIGDECIMALFLOAT64 |
| STRING | STRING |
| DATE | DATE |
| TIME | TIME |
| DATETIME | DATETIME |
| TIMESTAMP | TIMESTAMP |
| BYTES | BYTES |
| STRUCT | STRUCT with the same field position types. |
| ARRAY | ARRAY with the same element types. |
| GEOGRAPHY | GEOGRAPHY |
| RANGE | RANGE with the same subtype. |
If you want to find the supertype for a set of input types, first determine the intersection of the set of supertypes for each input type. If that set is empty then the input types have no common supertype. If that set is non-empty, then the common supertype is generally themost specific type in that set. Generally, the most specific type is the type with the most restrictive domain.
Examples
| Input types | Common supertype | Returns | Notes |
|---|---|---|---|
| INT64FLOAT64 | FLOAT64 | FLOAT64 | If you apply supertyping to INT64 andFLOAT64, supertyping succeeds because they they share a supertype,FLOAT64. |
| INT64BOOL | None | Error | If you apply supertyping to INT64 and BOOL, supertyping fails because they don't share a common supertype. |
Exact and inexact types
Numeric types can be exact or inexact. For supertyping, if all of the input types are exact types, then the resulting supertype can only be an exact type.
The following table contains a list of exact and inexact numeric data types.
| Exact types | Inexact types |
|---|---|
| INT64NUMERICBIGNUMERIC | FLOAT64 |
Examples
| Input types | Common supertype | Returns | Notes |
|---|---|---|---|
| INT64FLOAT64 | FLOAT64 | FLOAT64 | If supertyping is applied to INT64 and FLOAT64, supertyping succeeds because there are exact and inexact numeric types being supertyped. |
Types specificity
Each type has a domain of values that it supports. A type with a narrow domain is more specific than a type with a wider domain. Exact types are more specific than inexact types because inexact types have a wider range of domain values that are supported than exact types. For example,INT64 is more specific than FLOAT64.
Supertypes and literals
Supertype rules for literals are more permissive than for normal expressions, and are consistent with implicit coercion rules. The following algorithm is used when the input set of types includes types related to literals:
- If there exists non-literals in the set, find the set of common supertypes of the non-literals.
- If there is at least one possible supertype, find themost specific type to which the remaining literal types can be implicitly coerced and return that supertype. Otherwise, there is no supertype.
- If the set only contains types related to literals, compute the supertype of the literal types.
- If all input types are related to
NULLliterals, then the resulting supertype isINT64. - If no common supertype is found, an error is produced.
Examples
| Input types | Common supertype | Returns |
|---|---|---|
| INT64 literal UINT64 expression | UINT64 | UINT64 |
| TIMESTAMP expression STRING literal | TIMESTAMP | TIMESTAMP |
| NULL literal NULL literal | INT64 | INT64 |
| BOOL literal TIMESTAMP literal | None | Error |