[BUG] Casting rounded float to string returns "0E0" instead of "0.0"

[penghuo]

What is the bug?
Casting rounded float to string returns "0E0" instead of "0.0"

How can one reproduce the bug?

source=test002 
| eval vv=round((cast(1 as double)/100000)*100, 2) 
| eval sv=cast(vv as string) 
| fields sv

sv = "0E0"

What is the expected behavior?

sv = "0.0"

What is your host/environment?

• OS: [e.g. iOS]
• Version [e.g. 22]
• Plugins

Do you have any screenshots?
n/a

Do you have any additional context?
n/a

[yuancu]

Root cause:

Calcite's builtin cast operator leverages the following implementation ( from
https://github.com/apache/calcite/blob/cfaadedd8fd34c480395f9e843a73bf4bb8fe459/core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java#L4430)

  /** CAST(DOUBLE AS VARCHAR). */
  public static String toString(double x) {
    if (x == 0) {
      return "0E0";
    }
    return Double.toString(x);
  }

If the input equals to 0, it returns a hard-coded 0E0.

[yuancu]

Btw, I found that casting decimal to string also has special rules in Calcite:

... | eval s1 = cast(0.0 as string), s2 = cast(0.99 as string)

s1 = ".0"
s2 = ".99"

This may not be a bug, but it does cause disparity with the behavior of v2.

[LantaoJin]

Em, I think we should fix them both. ".99" is a not making sense. If we fix "0E0" to "0.0", no reason to keep the ".0". @yuancu