dawidwys commented on code in PR #22785:
URL: https://github.com/apache/flink/pull/22785#discussion_r1242395208
##########
flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/api/internal/BaseExpressions.java:
##########
@@ -1408,6 +1409,24 @@ public OutType arrayUnion(InType array) {
unresolvedCall(ARRAY_UNION, toExpr(),
objectToExpression(array)));
}
+ /**
+ * Returns a string that represents the concatenation of the elements in
the given array and the
+ * elements' data type in the given array is string. The `delimiter` is a
string that separates
+ * each pair of consecutive elements of the array. The optional
`nullReplacement` is a string
+ * that replaces null elements in the array.
+ *
+ * <p>Returns null if input array or delimiter or nullReplacement are null.
+ */
+ public OutType arrayJoin(InType delimiter, InType... nullReplacement) {
Review Comment:
Can we accept multiple null replacements? Shouldn't we rather overload it:
```
public OutType arrayJoin(InType delimiter);
public OutType arrayJoin(InType delimiter, InType nullReplacement);
```
##########
flink-table/flink-table-common/src/main/java/org/apache/flink/table/functions/BuiltInFunctionDefinitions.java:
##########
@@ -285,6 +286,20 @@ ANY, and(logical(LogicalTypeRoot.BOOLEAN), LITERAL)
"org.apache.flink.table.runtime.functions.scalar.ArrayUnionFunction")
.build();
+ public static final BuiltInFunctionDefinition ARRAY_JOIN =
+ BuiltInFunctionDefinition.newBuilder()
+ .name("ARRAY_JOIN")
+ .kind(SCALAR)
+ .inputTypeStrategy(
+ varyingSequence(
+ new
ArrayOfStringArgumentTypeStrategy("ARRAY<STRING>"),
+
logical(LogicalTypeFamily.CHARACTER_STRING),
+
logical(LogicalTypeFamily.CHARACTER_STRING)))
Review Comment:
The null replacement is an optional argument, not a var arg, isn't it?
Please take a look here:
https://github.com/apache/flink/blob/cc6ccecf9232d3bd8bfe8cb46207fbc92769a9e3/flink-table/flink-table-common/src/main/java/org/apache/flink/table/functions/BuiltInFunctionDefinitions.java#L106
how it can be done.
##########
flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/inference/strategies/ArrayOfStringArgumentTypeStrategy.java:
##########
@@ -0,0 +1,84 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.table.types.inference.strategies;
+
+import org.apache.flink.annotation.Internal;
+import org.apache.flink.table.functions.FunctionDefinition;
+import org.apache.flink.table.types.DataType;
+import org.apache.flink.table.types.inference.ArgumentTypeStrategy;
+import org.apache.flink.table.types.inference.CallContext;
+import org.apache.flink.table.types.inference.Signature.Argument;
+import org.apache.flink.table.types.logical.ArrayType;
+import org.apache.flink.table.types.logical.LogicalTypeRoot;
+
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+
+/** Strategy for an argument that must be an array of strings. */
+@Internal
+public final class ArrayOfStringArgumentTypeStrategy implements
ArgumentTypeStrategy {
+
+ private final String constraintMessage;
+
+ public ArrayOfStringArgumentTypeStrategy(String constraintMessage) {
+ this.constraintMessage = constraintMessage;
+ }
+
+ @Override
+ public Optional<DataType> inferArgumentType(
+ CallContext callContext, int argumentPos, boolean throwOnFailure) {
+
+ final List<DataType> actualDataTypes =
callContext.getArgumentDataTypes();
+ DataType actualType = actualDataTypes.get(argumentPos);
+
+ // Check if the type is an array and its element is string
+ if (actualType.getLogicalType().getTypeRoot() == LogicalTypeRoot.ARRAY
+ && (((ArrayType)
actualType.getLogicalType()).getElementType().getTypeRoot()
+ == LogicalTypeRoot.VARCHAR
+ || ((ArrayType)
actualType.getLogicalType()).getElementType().getTypeRoot()
+ == LogicalTypeRoot.CHAR)) {
+ return Optional.of(actualType);
+ }
Review Comment:
We should rather check if we can implicitly cast to `VARCHAR`. You can
reuse:
https://github.com/apache/flink/blob/fbc086f2fd63dac4af3e104ba4011e864781139a/flink-table/flink-table-common/src/main/java/org/apache/flink/table/types/inference/strategies/StrategyUtils.java#L56
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