Translating a QueryExpression into SQL: what's a Natural join?

I am trying to translate a QueryExpression that is in some existing code into a T-SQL select statement.

I've run across the following statement and I'm having trouble understanding what they mean by a Natural Join:

linkEntity1.JoinOperator = JoinOperator.Natural;

Would this be equivalent to an Inner Join in T-SQL? Googling has not been much help.

Here's the rest of the QueryExpression Code:

QueryExpression query = new QueryExpression();

query.EntityName = "showinfo";

ColumnSet columns = new ColumnSet();
columns.Attributes = new String[] { "company" };
query.ColumnSet = columns;

query.Criteria = new FilterExpression();
query.Criteria.FilterOperator = LogicalOperator.And;

ConditionExpression condition1 = new ConditionExpression();
condition1.AttributeName = "company";
condition1.Operator = ConditionOperator.NotNull;
query.Crite开发者_JS百科ria.Conditions = new ConditionExpression[] { condition1 };

LinkEntity linkEntity1 = new LinkEntity();
linkEntity1.JoinOperator = JoinOperator.Natural;
linkEntity1.LinkFromEntityName = "show";
linkEntity1.LinkFromAttributeName = "showid";
linkEntity1.LinkToEntityName = "showintegration";
linkEntity1.LinkToAttributeName = "showcode";

linkEntity1.LinkCriteria = new FilterExpression();
linkEntity1.LinkCriteria.FilterOperator = LogicalOperator.And;

ConditionExpression condition2 = new ConditionExpression();
condition2.AttributeName = "showend";
condition2.Operator = ConditionOperator.Null;

linkEntity1.LinkCriteria.Conditions = new ConditionExpression[] { condition2 };
query.LinkEntities = new LinkEntity[] { linkEntity1 };

There is no equivalent in SQL Server of a natural join where table intersect is based on column names by the RDBMS.

I'm glad of that because it is at best ambiguous and at worst dangerous. JOINs should be explicit. Examples why:

• having a InsertedBy column in both tables (quite common): should we have to prefix with the table name to remove ambiguity?
• future DDL that add columns that change JOIN semantics

See

• Natural join in SQL Server
• SQL Server - lack of NATURAL JOIN / x JOIN y USING(field)

Edit:

It looks like natural join means "don't repeat the column in the output" (like USING in MySQL would do) according to the JoinOperator Enumeration.

If I understand this (debatable!) it's misleading. Especially when I read the "LeftOuter" narrative..

A natural join compares all columns in the two tables that have the same column names. It's equivalent to an inner join with the matching columns explicitly listed.

Yes - the natural join is inner join - so you can write:

select * from tab1, tab2 where tab1.col1 = tab2.col1

as

select * from tab1 inner join tab2 on tab1.col1 = tab2.col1