flink 1.18.0
例如我写下一条SQL：
select * from KafkaTable where id is not null;
IS NOT NULL应该属于系统内建函数，于是我找到相关代码：
public static final BuiltInFunctionDefinition IS_NOT_NULL =
BuiltInFunctionDefinition.newBuilder()
.name("isNotNull")
.kind(SCALAR)
.inputTypeStrategy(wildcardWithCount(ConstantArgumentCount.of(1)))
.outputTypeStrategy(explicit(DataTypes.BOOLEAN().notNull()))
.build();
发现他的name是“ isNotNull”，和“is not null”对应不上。并且经过实际测验，确实证实了我的猜想：
DEBUG org.apache.flink.table.module.ModuleManager [] - Cannot
find FunctionDefinition 'is not null' from any loaded modules.
所以我很疑惑，SQL到底是在哪里找到了”is not null”这个函数的呢？
以下是调用栈：
@org.apache.flink.table.planner.catalog.FunctionCatalogOperatorTable.lookupOperatorOverloads()
at
org.apache.calcite.sql.util.ChainedSqlOperatorTable.lookupOperatorOverloads(ChainedSqlOperatorTable.java:69)
at
org.apache.calcite.sql.SqlUtil.lookupSubjectRoutinesByName(SqlUtil.java:609)
at
org.apache.calcite.sql.SqlUtil.lookupSubjectRoutines(SqlUtil.java:535)
at org.apache.calcite.sql.SqlUtil.lookupRoutine(SqlUtil.java:486)
at org.apache.calcite.sql.SqlOperator.deriveType(SqlOperator.java:595)
at
org.apache.calcite.sql.validate.SqlValidatorImpl$DeriveTypeVisitor.visit(SqlValidatorImpl.java:6302)
at
org.apache.calcite.sql.validate.SqlValidatorImpl$DeriveTypeVisitor.visit(SqlValidatorImpl.java:6287)
at org.apache.calcite.sql.SqlCall.accept(SqlCall.java:161)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.deriveTypeImpl(SqlValidatorImpl.java:1869)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.deriveType(SqlValidatorImpl.java:1860)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validateWhereOrOn(SqlValidatorImpl.java:4341)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validateWhereClause(SqlValidatorImpl.java:4333)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validateSelect(SqlValidatorImpl.java:3606)
at
org.apache.calcite.sql.validate.SelectNamespace.validateImpl(SelectNamespace.java:64)
at
org.apache.calcite.sql.validate.AbstractNamespace.validate(AbstractNamespace.java:89)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validateNamespace(SqlValidatorImpl.java:1050)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validateQuery(SqlValidatorImpl.java:1025)
at org.apache.calcite.sql.SqlSelect.validate(SqlSelect.java:248)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validateScopedExpression(SqlValidatorImpl.java:1000)
at
org.apache.calcite.sql.validate.SqlValidatorImpl.validate(SqlValidatorImpl.java:749)
at
org.apache.flink.table.planner.calcite.FlinkPlannerImpl.org$apache$flink$table$planner$calcite$FlinkPlannerImpl$$validate(FlinkPlannerImpl.scala:196)
at
org.apache.flink.table.planner.calcite.FlinkPlannerImpl.validate(FlinkPlannerImpl.scala:117)
at
org.apache.flink.table.planner.operations.SqlNodeToOperationConversion.convert(SqlNodeToOperationConversion.java:261)
at
org.apache.flink.table.planner.delegation.ParserImpl.parse(ParserImpl.java:106)
at
org.apache.flink.table.gateway.service.operation.OperationExecutor.executeStatement(OperationExecutor.java:187)
at
org.apache.flink.table.gateway.service.SqlGatewayServiceImpl.lambda$executeStatement$1(SqlGatewayServiceImpl.java:212)
at
org.apache.flink.table.gateway.service.operation.OperationManager.lambda$submitOperation$1(OperationManager.java:119)
at
org.apache.flink.table.gateway.service.operation.OperationManager$Operation.lambda$run$0(OperationManager.java:258)
at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:750)
