Reprint: SQL statements use aliases in where to judge conditions

Original address: http://www.cnblogs.com/dwfbenben/p/3307941.html

When we use an expression as a column of output, we cannot use that column directly in the Where condition as a criterion. For example, the following SQL statement:select id (C1 + C2 ) as s from t1  where s > 100 & nbsp SQL Server Error:      Select Id (C1 + c2) as s from t1  where (C1 + c2) >

The

is no problem.   But when the expression is complex, it is cumbersome.     is there a way to use such a column name in the Where?   or is there any other way to solve such problems? Workaround:

sql code copy code

 select t2. *from  (select id (C1 + c2) as C from t1 T2 where C > + --or select t2.< span class= "C" >*from  (select id, C  = C1+c2 from t1 T2where C > 100
                                                  

                        because column aliases cannot be used directly in the where statement, we need to wrap the SQL statement                         in Oracle, referencing column aliases in a WHERE clause can be an error , what is this for?                         because: The order of execution of the SELECT statement                         1. From Statement                         2. Where statement (binding condition)                         3. Start with statement            &Nbsp;           4. Connect by Statement                         5. Where statement                         6. GROUP BY Statement                         7. Having statements                         8. Model Statement                         9. SELECT statement                         10. Union, minus, intersect, etc. set calculus calculus     &NBSp;                  11. ORDER BY statement

Reprint: SQL statements use aliases in where to determine conditions