Replace this "switch" statement by "if" statements to increase readability.

Code Path:server/src/main/java/org/apache/iotdb/db/mpp/plan/analyze/ExpressionUtils.java

switch statements are useful when there are many different cases depending on the value of the same expression. For just one or two cases however, the code will be more readable with if statements.

Open server/src/main/java/org/apache/iotdb/db/mpp/plan/analyze/ExpressionUtils.java and inspect the switch statement identified by the issue. Replace it with equivalent if statements for the existing cases, then verify that the file still compiles and the relevant checks pass.

Written by the indexing model from the issue text.