sql中去重的方式有哪些

sql
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2023/8/2 12:04:56
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在SQL中,可以使用以下方式进行去重:

  1. 使用DISTINCT关键字:SELECT DISTINCT column1, column2 FROM table_name;
  2. 使用GROUP BY子句:SELECT column1, column2 FROM table_name GROUP BY column1, column2;
  3. 使用HAVING子句:SELECT column1, column2 FROM table_name GROUP BY column1, column2 HAVING COUNT(*) > 1;
  4. 使用ROW_NUMBER()函数:WITH cte AS (SELECT column1, column2, ROW_NUMBER() OVER (PARTITION BY column1, column2 ORDER BY column1, column2) AS rn FROM table_name) SELECT column1, column2 FROM cte WHERE rn = 1;
  5. 使用UNION或UNION ALL操作符:SELECT column1, column2 FROM table1 UNION SELECT column1, column2 FROM table2;
  6. 使用EXISTS子查询:SELECT column1, column2 FROM table_name t1 WHERE NOT EXISTS (SELECT 1 FROM table_name t2 WHERE t1.column1 = t2.column1 AND t1.column2 = t2.column2 AND t1.column3 = t2.column3);
  7. 使用TEMPORARY TABLE或CTE:CREATE TEMPORARY TABLE temp_table AS SELECT DISTINCT column1, column2 FROM table_name; SELECT * FROM temp_table;
  8. 使用窗口函数:SELECT column1, column2 FROM (SELECT column1, column2, ROW_NUMBER() OVER (PARTITION BY column1, column2 ORDER BY column1, column2) AS rn FROM table_name) AS subquery WHERE rn = 1;

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