rubenada commented on code in PR #3258:
URL: https://github.com/apache/calcite/pull/3258#discussion_r1231883768
##########
core/src/main/java/org/apache/calcite/sql/fun/SqlLibraryOperators.java:
##########
@@ -831,16 +831,43 @@ static RelDataType deriveTypeSplit(SqlOperatorBinding
operatorBinding,
new SqlLikeOperator("NOT RLIKE", SqlKind.RLIKE, true, true);
/** The "CONCAT(arg, ...)" function that concatenates strings.
- * For example, "CONCAT('a', 'bc', 'd')" returns "abcd". */
- @LibraryOperator(libraries = {MYSQL, POSTGRESQL, BIG_QUERY})
+ * For example, "CONCAT('a', 'bc', 'd')" returns "abcd".
+ *
+ * <p>It accepts at least 1 argument and returns null if any of
+ * the arguments is null. */
+ @LibraryOperator(libraries = {MYSQL, BIG_QUERY})
public static final SqlFunction CONCAT_FUNCTION =
SqlBasicFunction.create("CONCAT",
ReturnTypes.MULTIVALENT_STRING_SUM_PRECISION_NULLABLE,
- OperandTypes.repeat(SqlOperandCountRanges.from(2),
+ OperandTypes.repeat(SqlOperandCountRanges.from(1),
OperandTypes.STRING),
SqlFunctionCategory.STRING)
.withOperandTypeInference(InferTypes.RETURN_TYPE);
+ /** The "CONCAT(arg, ...)" function that concatenates strings,
+ * which never returns null.
+ * For example, "CONCAT('a', 'bc', 'd')" returns "abcd".
+ *
+ * <p>If one of the arguments is null, it will be treated as empty string.
+ * "CONCAT('a', null)" returns "a".
+ * "CONCAT('a', null, 'b')" returns "ab".
+ *
+ * <p>Returns empty string only when all arguments are null.
Review Comment:
Nit pick: this does not seem entirely correct, I assume it should be
"Returns empty string only when all arguments are null *or the empty string"*,
is that correct?
```
"CONCAT('')" returns ""
"CONCAT('', null, '')" returns ""
```
Maybe the new tests added by this PR should have some scenarios with the
empty string, just to cover these cases.
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