Write custom H2 DB function Java - spring-boot

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 days) 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.