private void GenerateSetOperationHelper(SetOperationBase setOperation)
{
_relationalCommandBuilder.AppendLine("(");
using (_relationalCommandBuilder.Indent())
{
this.GenerateSetOperation(setOperation);
}
_relationalCommandBuilder.AppendLine()
.Append(")")
.Append(AliasSeparator)
.Append(_sqlGenerationHelper.DelimitIdentifier(setOperation.Alias));
}
protected virtual void GenerateSetOperation(SetOperationBase setOperation)
{
string getSetOperation() => setOperation switch
{
ExceptExpression _ => "EXCEPT",
IntersectExpression _ => "INTERSECT",
UnionExpression _ => "UNION",
_ => throw new InvalidOperationException("Unknown SetOperationType."),
};
GenerateSetOperationOperand(setOperation, setOperation.Source1);
_relationalCommandBuilder.AppendLine();
_relationalCommandBuilder.AppendLine($"{getSetOperation()}{(setOperation.IsDistinct ? "" : " ALL")}");
GenerateSetOperationOperand(setOperation, setOperation.Source2);
}
protected virtual void GenerateSetOperationOperand(SetOperationBase setOperation, SelectExpression operand)
{
// INTERSECT has higher precedence over UNION and EXCEPT, but otherwise evaluation is left-to-right.
// To preserve meaning, add parentheses whenever a set operation is nested within a different set operation.
if (IsNonComposedSetOperation(operand) &&
operand.Tables[0].GetType() != setOperation.GetType())
{
_relationalCommandBuilder.AppendLine("(");
using (_relationalCommandBuilder.Indent())
{
Visit(operand);
}
_relationalCommandBuilder.AppendLine().Append(")");
}
else
{
Visit(operand);
}
}
