How can I use CONCAT()
and GROUP_CONCAT()
in HQL queries?
About concat
: it works exactly the same way as it does in MySQL (it concatenates strings, it is not an aggregate function).
You can add group_concat
as an sql function to your configuration. This way you assume that the underlaying DB knows this function, and you tie your program to MySQL.
import org.hibernate.cfg.Configuration;
import org.hibernate.dialect.function.StandardSQLFunction;
import org.hibernate.type.StringType;
// ...
myConf.addSqlFunction("group_concat", new StandardSQLFunction("group_concat", new StringType()));
You also indicate that the output of the function is a string. Without this when you group_concat
numeric fields Hibernate will assume the result also to be numeric and crash.