fix: Add user-friendly error message for SELECT null AS column (#8276)

confluentinc · Oct 25, 2021 · 57b7dea · 57b7dea
1 parent 2cb82cd
commit 57b7dea
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diff --git a/ksqldb-engine/src/main/java/io/confluent/ksql/planner/plan/SelectionUtil.java b/ksqldb-engine/src/main/java/io/confluent/ksql/planner/plan/SelectionUtil.java
@@ -126,6 +126,10 @@ public static LogicalSchema buildProjectionSchema(
       } else {
         final Expression expression = select.getExpression();
         final SqlType type = expressionTypeManager.getExpressionSqlType(expression);
+        if (type == null) {
+          throw new IllegalArgumentException("Can't infer a type of null. Please explicitly cast "
+              + "it to a required type, e.g. CAST(null AS VARCHAR).");
+        }
         builder.valueColumn(select.getAlias(), type);
       }
     }

diff --git a/ksqldb-functional-tests/src/test/resources/query-validation-tests/null.json b/ksqldb-functional-tests/src/test/resources/query-validation-tests/null.json
@@ -260,6 +260,17 @@
         "message": "Invalid comparison expression 'null' in join '(L.A = null)'. Each side of the join comparision must contain references from exactly one source."
       }
     },
+    {
+      "name": "null as column",
+      "statements": [
+        "CREATE STREAM INPUT (COL0 INT KEY) WITH (kafka_topic='test_topic', value_format='JSON');",
+        "CREATE STREAM OUTPUT AS SELECT COL0, null as COL2 FROM INPUT;"
+      ],
+      "expectedException": {
+        "type": "io.confluent.ksql.util.KsqlStatementException",
+        "message": "Can't infer a type of null. Please explicitly cast it to a required type, e.g. CAST(null AS VARCHAR)."
+      }
+    },
     {
       "name": "null if",
       "statements": [