(mysql.info.gz) Problems with alias

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 A.5.4 Problems with Column Aliases
 ----------------------------------
 
 You can use an alias to refer to a column in `GROUP BY', `ORDER BY', or
 `HAVING' clauses.  Aliases can also be used to give columns better
 names:
 
      SELECT SQRT(a*b) AS root FROM TBL_NAME GROUP BY root HAVING root > 0;
      SELECT id, COUNT(*) AS cnt FROM TBL_NAME GROUP BY id HAVING cnt > 0;
      SELECT id AS 'Customer identity' FROM TBL_NAME;
 
 Standard SQL doesn't allow you to refer to a column alias in a `WHERE'
 clause.  This is because when the `WHERE' code is executed, the column
 value may not yet be determined. For example, the following query is
 illegal:
 
      SELECT id, COUNT(*) AS cnt FROM TBL_NAME WHERE cnt > 0 GROUP BY id;
 
 The `WHERE' statement is executed to determine which rows should be
 included in the `GROUP BY' part, whereas `HAVING' is used to decide
 which rows from the result set should be used.
 

Info Catalog

(mysql.info.gz) Problems with NULL

(mysql.info.gz) Query Issues

(mysql.info.gz) Non-transactional tables