Write custom H2 DB function Java

Question

I am trying to run the below code using H2DB (via junit test), while doing so i get error message as below. I understand that, there are no function available as "days" in H2. So i am trying to write a custom function, but it does not work out, can any one help on writing this function.

SQLBuilder class code:

public String dummy() {
        return new StringBuilder(new SQL() {
            {
                SELECT("date(CREATE_TMS)");
                SELECT("CASE WHEN date(CREATE_TMS) >= (CURRENT DATE - cast('1' AS integer) days) THEN 'Y' ELSE 'N' END NEW_B");
                FROM("Q.DUMMY");
            }
        }.toString().concat(" FOR READ ONLY WITH UR")).toString();
    }

Error message:

org.springframework.jdbc.BadSqlGrammarException: 
### Error querying database.  Cause: org.h2.jdbc.JdbcSQLSyntaxErrorException: Syntax error in SQL statement "SELECT DATE(CREATE_TMS), CASE WHEN DATE(CREATE_TMS) >= (CURRENT DATE - CAST('1' AS INTEGER) DAYS[*]) THEN 'Y' ELSE 'N' END NEW_BILLING
FROM Q.DUMMY FOR READ ONLY WITH UR "; expected "[, ::, *, /, %, +, -, ||, ~, !~, NOT, LIKE, ILIKE, REGEXP, IS, IN, BETWEEN, AND, OR, ,, )"; SQL statement:
SELECT date(CREATE_TMS), CASE WHEN date(CREATE_TMS) >= (CURRENT DATE - cast('1' AS integer) days) THEN 'Y' ELSE 'N' END NEW_BILLING
FROM Q.DUMMY FOR READ ONLY WITH UR [42001-199]

For some reason days are converted to DAYS[*] , we can see that in error message.

Customer method i tried in schema-db2.sql:

drop ALIAS if exists days; 
CREATE ALIAS days as '
import java.lang.String;
@CODE
java.lang.String days() throws Exception { 
  return "days";
} 
';

applicaiton.properties:

spring.datasource.url=jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=false;Mode=DB2

Answer 1

DAYS is not a function and is not a something that other databases support. Db2 also uses non-standard interval literals.

If you can build H2 from its current sources, you can use cast('1' AS integer) day in it (not the day s ) and such construction is also supported by Db2. You can also simply use 1 DAY , it is supported by current H2 and Db2 too.

(CURRENT_DAY - 1 DAY)

Sources of H2 are available on GitHub:

https://github.com/h2database/h2database

Building instructions are here:

https://h2database.com/html/build.html#building

You need a jar target.

To compile H2 from the current sources you need JDK 8, 9, 10, 11, or 12. Compiled jar will be compatible with more recent versions.