Often, I have seen developers use code that does not conform to the ANSI standards. The reasons are many, but that is not we are discussing today. What we would discuss is that these non-standard practices need to be stopped, in some cases, by eliminating the feature all-together. The result of this effort is that the code ends up in a lot of rework because the product (in this case, Microsoft SQL Server) ends up either adopting newer standards or discontinuing support of the older, non-standardized code.
One such coding practice is the use of non-ANSI standard OUTER operators (*= and =*, for right outer join and left outer join respectively). Such code would typically look like:
FROM EmployeeTerritories, Territories
WHERE EmployeeTerritories.TerritoryID =* Territories.TerritoryID
Effectively, the operator *= indicates that all rows from the left table need to be taken and matched with those on the right-hand side table, i.e. it is similar to a LEFT OUTER JOIN. Similarly, the operator =* is the RIGHT OUTER JOIN.
Running such code on any database with a compatibility level of 90 or higher (SQL Server 2005 or higher) will result in the following error:
Msg 4147, Level 15, State 1, Line 3
The query uses non-ANSI outer join operators ("*=" or "=*"). To run this query without modification, please set the compatibility level for current database to 80, using the SET COMPATIBILITY_LEVEL option of ALTER DATABASE. It is strongly recommended to rewrite the query using ANSI outer join operators (LEFT OUTER JOIN, RIGHT OUTER JOIN). In the future versions of SQL Server, non-ANSI join operators will not be supported even in backward-compatibility modes.
The solution to this is to use the ANSI standard, SQL-92 syntax of LEFT and RIGHT OUTER JOIN. The query above, can therefore be represented in ANSI standard code as:
RIGHT OUTER JOIN Territories ON EmployeeTerritories.TerritoryID = Territories.TerritoryID
If yours is a product that has evolved from the days when Microsoft SQL Server was in it’s infancy, then chances are that fragments of your code still uses such non-ANSI standard code. It would be a good idea to take a couple of days to revisit the code and make it ANSI compliant to avoid further rework.
Until we meet next time,
Be courteous. Drive responsibly.