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更新时间：2024-04-18 GMT+08:00
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子句顺序

从Teradata迁移SELECT语句时，各子句（FROM、WHERE、HAVING和GROUP BY）可按任意顺序排列。如果语句的FROM子句之前包含作为ALIAS的QUALIFY子句，则DSC不会迁移该语句。

可以使用tdMigrateALIAS参数来配置ALIAS的迁移。

输入：子句顺序

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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 ;

输出

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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 <> '' ;

输入：子句顺序

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

输出

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

如果输入脚本的FROM子句之前包含作为ALIAS的QUALIFY子句，DSC将不会迁移该语句，也不会逐字复制输入的语句。

输入：子句顺序，在FROM子句之前使用QUALIFY作为ALIAS

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

输出

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