Type Conversion

In Doris, each expression has a type, such as 1, col1, and from_unixtime(col2) in the expression select 1, col1, from_unixtime(col2) from table1. The process of converting an expression from one type to another is called "type conversion."

Type conversion occurs in two cases: explicit conversion and implicit conversion.

All type conversions follow specific rules. We describe the related rules according to the target type of the conversion. For example, converting from INT to DOUBLE and converting from STRING to DOUBLE are both described in the Conversion to FLOAT/DOUBLE document.

Whether a conversion can occur and whether the result is a nullable type depends on whether strict mode is enabled (session variable enable_strict_cast). Generally, when strict mode is enabled, data that fails conversion will immediately cause an error and result in SQL failure. When strict mode is disabled, data rows that fail conversion will result in NULL.

Explicit Conversion

Explicit conversion is done through the CAST function, for example:

CAST(1.23 as INT) converts the number 1.23 to INT type.

CAST(colA as DATETIME(6)) converts the column/expression colA to DATETIME(6) type (i.e., a DATETIME type with microsecond precision).

The following describes the type conversion relationships between different types under strict mode (enable_strict_cast = true) and non-strict mode (enable_strict_cast = false), including the following four cases:

Symbol	Meaning
x	Not allowed to convert
P	The return type will be Nullable only when the input parameter is already a Nullable type, i.e., the conversion will not convert non-Null values to Null
A	The return type is always Nullable. The conversion may convert non-Null values to Null
O	The return type is Nullable when the conversion from input type to output type may cause overflow. For non-Null input values, if the conversion actually causes overflow, the conversion result may be Null

The specific type conversion rules and Nullable properties, please check the type conversion documents in the current directory.

Strict Mode

From\To	bool	tinyint	smallint	int	bigint	largeint	float	double	decimal	date	datetime	time	IPv4	IPv6	char	varchar	string	bitmap	hll	json	array	map	struct
bool	P	P	P	P	P	P	P	P	P	x	x	x	x	x				x	x	P	x	x	x
tinyint	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
smallint	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
int	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
bigint	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
largeint	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
float	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
double	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
decimal	P	P	P	P	P	P	P	P	P	P	P	P	x	x				x	x	P	x	x	x
date	x	x	x	P	P	P	x	x	x	P	P	x	x	x				x	x	x	x	x	x
datetime	x	x	x	x	P	P	x	x	x	P	P	P	x	x				x	x	x	x	x	x
time	x	P	P	P	P	P	x	x	x	P	P	P	x	x				x	x	x	x	x	x
IPv4	x	x	x	x	x	x	x	x	x	x	x	x	P	P				x	x	x	x	x	x
IPv6	x	x	x	x	x	x	x	x	x	x	x	x	x	P				x	x	x	x	x	x
char	P	P	P	P	P	P	P	P	P	P	P	P	P	P				x	x	P	P	P	P
varchar	P	P	P	P	P	P	P	P	P	P	P	P	P	P				x	x	P	P	P	P
string	P	P	P	P	P	P	P	P	P	P	P	P	P	P				x	x	P	P	P	P
bitmap	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	P	x	x	x	x	x
hll	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	P	x	x	x	x
json	A	A	A	A	A	A	A	A	A	x	x	x	x	x	A	A	A	x	x	P	A	x	A
array	x	x	x	x	x	x	x	x	x	x	x	x	x	x				x	x	P	P	x	x
map	x	x	x	x	x	x	x	x	x	x	x	x	x	x				x	x	x	x	P	x
struct	x	x	x	x	x	x	x	x	x	x	x	x	x	x				x	x	P	x	x	P
variant

Non-strict Mode

From\To	bool	tinyint	smallint	int	bigint	largeint	float	double	decimal	date	datetime	time	IPv4	IPv6	char	varchar	string	bitmap	hll	json	array	map	struct
bool	P	P	P	P	P	P	P	P	O	x	x	x	x	x				x	x	P	x	x	x
tinyint	P	P	P	P	P	P	P	P	O	A	A	A	x	x				x	x	P	x	x	x
smallint	P	A	P	P	P	P	P	P	O	A	A	A	x	x				x	x	P	x	x	x
int	P	A	A	P	P	P	P	P	O	A	A	A	x	x				x	x	P	x	x	x
bigint	P	A	A	A	P	P	P	P	O	A	A	A	x	x				x	x	P	x	x	x
largeint	P	A	A	A	A	P	P	P	O	A	A	A	x	x				x	x	P	x	x	x
float	P	A	A	A	A	A	P	P	A	A	A	A	x	x				x	x	P	x	x	x
double	P	A	A	A	A	A	P	P	A	A	A	A	x	x				x	x	P	x	x	x
decimal	P	O	O	O	O	O	P	P	O	A	A	A	x	x				x	x	P	x	x	x
date	x	x	x	P	P	P	P	P	x	P	P	x	x	x				x	x	x	x	x	x
datetime	x	x	x	x	P	P	P	P	x	P	A	P	x	x				x	x	x	x	x	x
time	x	A	A	A	P	P	P	P	x	P	P	A	x	x				x	x	x	x	x	x
IPv4	x	x	x	x	x	x	x	x	x	x	x	x	P	P				x	x	x	x	x	x
IPv6	x	x	x	x	x	x	x	x	x	x	x	x	x	P				x	x	x	x	x	x
char	A	A	A	A	A	A	A	A	A	A	A	A	A	A				x	x	A	A	A	A
varchar	A	A	A	A	A	A	A	A	A	A	A	A	A	A				x	x	A	A	A	A
string	A	A	A	A	A	A	A	A	A	A	A	A	A	A				x	x	A	A	A	A
bitmap	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	P	x	x	x	x	x
hll	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	x	P	x	x	x	x
json	A	A	A	A	A	A	A	A	A	x	x	x	x	x	A	A	A	x	x	P	A	x	A
array	x	x	x	x	x	x	x	x	x	x	x	x	x	x				x	x	P	P	x	x
map	x	x	x	x	x	x	x	x	x	x	x	x	x	x				x	x	x	x	P	x
struct	x	x	x	x	x	x	x	x	x	x	x	x	x	x				x	x	P	x	x	P
variant

Implicit Conversion

Implicit conversion occurs in certain situations where the input SQL does not explicitly specify, but Doris automatically plans the CAST expression. It mainly occurs in scenarios such as:

When a function call is made, the type of the actual parameter does not match the type of the function signature.
When the types on both sides of a mathematical expression are inconsistent.

etc.

Conversion matrix

TODO

Common Type

When an implicit conversion is required due to the operands being used as mathematical operations, the first step is to determine the common type. If the operands on both sides are not consistent with the common type, each will plan a CAST expression to the common type.

TODO

Explicit Conversion​

Strict Mode​

Non-strict Mode​

Implicit Conversion​

Conversion matrix​

Common Type​