gengliangwang commented on code in PR #51146:
URL: https://github.com/apache/spark/pull/51146#discussion_r2162200500
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sql/catalyst/src/main/java/org/apache/spark/sql/connector/expressions/filter/AlwaysNull.java:
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@@ -0,0 +1,32 @@
+package org.apache.spark.sql.connector.expressions.filter;
+
+import org.apache.spark.annotation.Evolving;
+import org.apache.spark.sql.connector.expressions.Literal;
+import org.apache.spark.sql.types.DataType;
+import org.apache.spark.sql.types.DataTypes;
+
+/**
+ * A predicate that always evaluates to {@code null}.
+ *
+ * @since 4.1.0
+ */
+@Evolving
+public final class AlwaysNull extends Predicate implements Literal<Boolean> {
Review Comment:
Databases supports `CHECK(null)`:
* PostgreSQL
* Oracle
Databases doesn't support `CHECK(null)`:
* MySQL: `ERROR 3813 (HY000) at line 2: Column check constraint
'product_chk_1' references other column.`
* SQL server: The bare token NULL has no boolean meaning: `An expression of
non-boolean type specified in a context where a condition is expected`
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