mihaibudiu commented on code in PR #4353:
URL: https://github.com/apache/calcite/pull/4353#discussion_r2072653286
##########
core/src/main/java/org/apache/calcite/sql/validate/implicit/TypeCoercionImpl.java:
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@@ -422,6 +439,34 @@ protected boolean booleanEquality(SqlCallBinding binding,
return false;
}
+ /**
+ * COALESCE type coercion, collect all the branches types to find a common
type,
+ * then cast the operands to the common type when needed.
+ */
+ private boolean coalesceCoercion(SqlCallBinding callBinding) {
+ List<RelDataType> argTypes = new ArrayList<>();
+ SqlValidatorScope scope = getScope(callBinding);
+ for (SqlNode node : callBinding.operands()) {
+ argTypes.add(validator.deriveType(scope, node));
+ }
+ RelDataType widerType = getWiderTypeFor(argTypes, true);
+ if (null != widerType) {
+ return coerceOperandsType(scope, callBinding.getCall(), widerType);
+ }
+ return false;
+ }
+
+ /**
+ * NULLIF type coercion, cast the second operand type to the first operand
type when needed.
Review Comment:
Maybe there is a misunderstanding, I didn't say that the NULLIF coercion has
to be removed, I said it has to behave like the other two coercions, using the
wider type.
There is a commutative diagram which must hold at all times:
```
NULLIF ----------------> CASE
| coercion | coercion
v v
NULLIF-----------------> CASE
```
In other words, if you choose to expand NULLIF into CASE and then coerce, or
if you coerce first and then expand, you should get the exact same result. So
once you fix the coercion for CASE (which is fixed in the original code), you
get a fixed coercion rule for NULLIF. All this is true for COALESCE as well.
BTW: I would recommend putting this diagram in the comments of the coercion
for NULLIF; if someone implements a new validator, this rule has to be obeyed.
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