即兴的SQL查询

Question

我有以下sql需要1或2秒才能返回结果。我在游标中调用这个SQL 500多次。我正在尝试重新编写此查询。

SET @row_num=0;
SELECT * FROM 
(SELECT @row_num:=@row_num+1 AS `row_num`, t_table.* FROM t_table WHERE type_id>0 ORDER BY type_id ASC, type_place_id DESC, user_id DESC LIMIT 100) AS counted_view WHERE counted_view.row_num = {$current + 1};

请建议我如何以更好的方式重新编写此查询

Answer 1

不要过滤功能结果。找到替换它的方法：

AND month(OTDate) = Month(@FromDate)
AND year(OTDate) = Year(@FromDate)

这样的事情：

 and OTDate >= the first day of the month for @FromDate
 and OTDate < the first day of the month following @FromDate

Answer 2

首先，重新编写WHERE子句，如下所示：

SELECT . . .
FROM tbl_OTAuthorization
WHERE EmployeeCodeFK = @EmployeeCode AND
      OTDate >= DATEADD(day, 1 - DAY(@FromDate), @FromDate) AND
      OTDate < DATEADD(month, 1, DATEADD(@FromDate, 1 - DAY(@FromDate), @FromDate));

其次，为表创建适当的索引：

CREATE INDEX tbl_OTAuthorization_2 ON tbl_OTAuthorization(EmployeeCodeFK, OTDate, UpdatedAdjustedOT);

第三，返回并修复您的代码，使其不会在员工和日期之间循环。您应该能够在单个查询中处理逻辑。通常，如果要优化使用数据库的性能，请避免使用游标。

Answer 3

试试这个：

SELECT Sum(CONVERT(DECIMAL(18, 2), ISNULL(NULLIF(UpdatedAdjustedOT, ''), 0))) as OTHours
    FROM tbl_OTAuthorization
    WHERE EmployeeCodeFK = @EmployeeCode
        AND month(OTDate) = Month(@FromDate)
        AND year(OTDate) = Year(@FromDate)

Answer 4

WHERE EmployeeCodeFK = @EmployeeCode
    AND OTDate >= DATEADD(MONTH, DATEDIFF(MONTH, 0, @FromDate), 0)
    AND OTDate < DATEADD(MONTH, 1, DATEADD(MONTH, DATEDIFF(MONTH, 0, @FromDate), 0))