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HHH-465 - order by nulls first / last

This commit is contained in:
Steve Ebersole 2015-03-25 09:34:45 -05:00
parent 52fabe70bc
commit 9901f85f77
1 changed files with 28 additions and 25 deletions
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53
hibernate-core/src/main/java/org/hibernate/dialect/DB2Dialect.java
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@ -48,7 +48,6 @@ import org.hibernate.exception.spi.SQLExceptionConversionDelegate;
import org.hibernate.internal.CoreLogging;
import org.hibernate.internal.CoreMessageLogger;
import org.hibernate.internal.util.JdbcExceptionHelper;
import org.hibernate.internal.util.StringHelper;
import org.hibernate.type.StandardBasicTypes;
import org.hibernate.type.descriptor.sql.SmallIntTypeDescriptor;
import org.hibernate.type.descriptor.sql.SqlTypeDescriptor;
@ -531,8 +530,8 @@ public class DB2Dialect extends Dialect {
}
/**
* DB2 allows NULLS LAST only if the order is ASC, and NULLS FIRST only if the order is DESC.
* Handle DB2 "support" for null precedence...
*
* @param expression The SQL order expression. In case of {@code @OrderBy} annotation user receives property placeholder
* (e.g. attribute name enclosed in '{' and '}' signs).
* @param collation Collation string in format {@code collate IDENTIFIER}, or {@code null}
@ -545,32 +544,36 @@ public class DB2Dialect extends Dialect {
*/
@Override
public String renderOrderByElement(String expression, String collation, String order, NullPrecedence nullPrecedence) {
// DB2 FTW!
if ( nullPrecedence == null || nullPrecedence == NullPrecedence.NONE ) {
return super.renderOrderByElement( expression, collation, order, NullPrecedence.NONE );
}
if ( nullPrecedence == NullPrecedence.FIRST ) {
// an explicit NullPrecedence request for NULLS FIRST
if ( order == null || "asc".equals( order ) ) {
// ASC + NULLS FIRST is ok, but unnecessary
return super.renderOrderByElement( expression, collation, order, NullPrecedence.NONE );
}
else {
// DESC + NULLS FIRST is not supported, so hack it
return "order by case when " + expression + " is null then 0 else 1 end, " + expression + " desc";
}
}
else {
// an explicit NullPrecedence request for NULLS LAST
if ( order == null || "asc".equals( order ) ) {
// ASC + NULLS LAST is not supported, so hack it
return "order by case when " + expression + " is null then 1 else 0 end, " + expression + " asc";
}
else {
// DESC + NULLS LAST is ok, but unnecessary
return super.renderOrderByElement( expression, collation, order, NullPrecedence.NONE );
}
// DB2 FTW! A null precedence was explicitly requested, but DB2 "support" for null precedence
// is a joke. Basically it supports combos that align with what it does anyway. Here is the
// support matrix:
// * ASC + NULLS FIRST -> case statement
// * ASC + NULLS LAST -> just drop the NULLS LAST from sql fragment
// * DESC + NULLS FIRST -> just drop the NULLS FIRST from sql fragment
// * DESC + NULLS LAST -> case statement
if ( ( nullPrecedence == NullPrecedence.FIRST && "desc".equalsIgnoreCase( order ) )
|| ( nullPrecedence == NullPrecedence.LAST && "asc".equalsIgnoreCase( order ) ) ) {
// we have one of:
// * ASC + NULLS LAST
// * DESC + NULLS FIRST
// so just drop the null precedence. *NOTE: we could pass along the null precedence here,
// but only DB2 9.7 or greater understand it; dropping it is more portable across DB2 versions
return super.renderOrderByElement( expression, collation, order, NullPrecedence.NONE );
}
return String.format(
Locale.ENGLISH,
"case when %s is null then %s else %s end, %s %s",
expression,
nullPrecedence == NullPrecedence.FIRST ? "0" : "1",
nullPrecedence == NullPrecedence.FIRST ? "1" : "0",
expression,
order
);
}
}