Help Center> Data Warehouse Service (DWS)> Tool Guide> DSC> SQL Syntax Migration Reference> Teradata Syntax Migration> Data Manipulation Language (DML)> SELECT> Order of Clauses
Updated on 2024-04-28 GMT+08:00
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Order of Clauses

For Teradata migration of SELECT statements, all the clauses (FROM, WHERE, HAVING and GROUP BY) can be listed in any order. The tool will not migrate the statement if it contains a QUALIFY as an ALIAS before the FROM clause.

Use the tdMigrateALIAS configuration parameter to configure migration of ALIAS.

Input: Order of Clauses

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SELECT expr1 AS alias1
      , expr2 AS alias2 
      , expr3 AS alias3
      , MAX( expr4 ), ...
   FROM tab1 T1 INNER JOIN tab2 T2
     ON T1.c1 = T2.c2 ...
    AND T3.c5 = '010'
    AND ...
  WHERE T1.c7 = '000'
    AND ...
 HAVING alias1 <> 'IC'
         AND alias2 <> 'IC'
         AND alias3 <> ''
  GROUP BY 1, 2, 3 ;

Output

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SELECT
          expr1 AS "alias1"
          ,expr2 AS "alias2"
          ,expr3 AS "alias3"
          ,MAX( expr4 )
          ,...
     FROM
          tab1 T1 INNER JOIN tab2 T2
               ON T1.c1 = T2.c2 ...
          AND T3.c5 = '010'
          AND ...
     WHERE
          T1.c7 = '000'
          AND ...
     GROUP BY
          1 ,2 ,3
     HAVING
          alias1 <> 'IC'
          AND alias2 <> 'IC'
          AND alias3 <> '' ;

Input: Order of Clauses

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SELECT
          TOP 10 *
     GROUP BY
          DeptNo
     WHERE
          empID < 100
FROM
          tbl_employee;

Output

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SELECT
          *
     FROM
          tbl_employee
     WHERE
          empID < 100
     GROUP BY
          DeptNo LIMIT 10
;

If the input script contains QUALIFY as an ALIAS before the FROM clause, the DSC will not migrate the statement and copy the input statement verbatim.

Input: Order of Clauses with QUALIFY as an ALIAS before the FROM clause

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SELECT
          *
     FROM
          table1
     WHERE
          abc = (
               SELECT
                         col1 AS qualify
                    FROM
                         TABLE
                         WHERE
                              col1 = 5
          )
;

Output

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SELECT
          *
     FROM
          table1
     WHERE
          abc = (
               SELECT
                         col1 AS qualify
                    FROM
                         TABLE
                         WHERE
                              col1 = 5
          )
;
Parent topic: SELECT