如何在HQL查询中使用CONCAT()
和GROUP_CONCAT()
?
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.
If you are using createSQLQuery, use addScalar to that column as String.
SQLQuery query = sessionObj.createSQLQuery("select group_concat(column1,column2) as mycolumn from some table group by someThing");
query.addScalar("mycolumn ", Hibernate.STRING);
subclass the dialect
and
registerFunction("group_concat", new StandardSQLFunction("group_concat", Hibernate.STRING));
or use SQLFunctionTemplate
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