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docs(sql): add FLOAT/REAL type casting and precision info 

- Add FLOAT and REAL to numeric types table
- Document precision differences (~7 vs ~15 significant digits)
- Add warning about precision loss when casting to FLOAT
- Note PostgreSQL behavior difference

Note: DAR-584 referenced Cloud Dedicated, but this behavior is shared
across all InfluxDB 3 products via DataFusion SQL engine.

Closes DAR-584
dar-584-float-precision
Jason Stirnaman 2026-02-19 16:49:03 -06:00
parent ba28e124b1
commit adfece559f
1 changed files with 32 additions and 7 deletions
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39
content/shared/sql-reference/data-types.md
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@ -61,11 +61,13 @@ during query execution and returned in query results.
The following numeric types are supported:
| SQL data type | Arrow data type | Description |
| :-------------- | :-------------- | :--------------------------- |
| BIGINT | INT64 | 64-bit signed integer |
| BIGINT UNSIGNED | UINT64 | 64-bit unsigned integer |
| DOUBLE | FLOAT64 | 64-bit floating-point number |
| SQL data type | Arrow data type | Description |
| :-------------- | :-------------- | :----------------------------------------- |
| BIGINT | INT64 | 64-bit signed integer |
| BIGINT UNSIGNED | UINT64 | 64-bit unsigned integer |
| DOUBLE | FLOAT64 | 64-bit floating-point number (~15 digits) |
| FLOAT | FLOAT32 | 32-bit floating-point number (~7 digits) |
| REAL | FLOAT32 | 32-bit floating-point number (alias for FLOAT) |
### Integers
@ -101,11 +103,22 @@ Unsigned integer literals are comprised of an integer cast to the `BIGINT UNSIGN
### Floats
InfluxDB SQL supports the 64-bit double floating point values.
Floats can be a decimal point, decimal integer, or decimal fraction.
InfluxDB SQL supports both 32-bit (single precision) and 64-bit (double precision) floating-point values.
| Type | Precision | Significant Digits | Use Case |
| :----- | :-------- | :----------------- | :------- |
| FLOAT | 32-bit | ~7 digits | Memory-efficient storage when full precision isn't needed |
| DOUBLE | 64-bit | ~15-16 digits | Default for most numeric operations |
> [!Note]
> InfluxDB stores float field values as 64-bit (FLOAT64) internally.
> Casting to FLOAT (32-bit) may lose precision for values with more than ~7 significant digits.
> Unlike PostgreSQL where FLOAT defaults to double precision, InfluxDB SQL treats FLOAT as single precision (32-bit).
##### Example float literals
Float literals are stored as 64-bit double precision:
```sql
23.8
-446.89
@ -113,6 +126,18 @@ Floats can be a decimal point, decimal integer, or decimal fraction.
0.033
```
##### Example float casting
```sql
-- Cast to 32-bit float (may lose precision)
SELECT 3.141592653589793::FLOAT;
-- Returns: 3.1415927 (truncated to ~7 digits)
-- Cast to 64-bit double (preserves precision)
SELECT 3.141592653589793::DOUBLE;
-- Returns: 3.141592653589793
```
## Date and time data types
InfluxDB SQL supports the following DATE/TIME data types: