我有一个包含一组数据的表，我想使用Mysql显示来自其中的特定记录：

Question

这是表格：很抱歉，此处无法正确显示表格。

Id  Date1   Rank1   date2     Rank2

100 1/1/01  1      1/2/01        1

100 1/2/01  1      1/3/01        1

100 1/3/01  1      1/5/01        4

现在，我想查看排名发生变化的结果，但date1应该显示从Rank = 1开始的日期，这样的输出：

Id    Date1    Rank1      date2    Rank2

100   1/1/01      1     1/5/01        4

谁能让我知道如何在MYSQL中执行此操作？ 我考虑过使用SQL游标，还有其他方法吗？

Answer 1

我将创建一个存储过程和一个游标以遍历每条记录。

我的存储过程将如下所示：

CREATE PROCEDURE `GetChangedRank`()
BEGIN

# Variables containing the final result
DECLARE ID INTEGER;
DECLARE DATE1 DATE;
DECLARE Rank1 INTEGER;
DECLARE DATE2 DATE;
DECLARE Rank2 INTEGER;

DECLARE ROWNUM INTEGER DEFAULT 0;

# Temporary variables to store values of each row.
DECLARE v_finished INTEGER DEFAULT 0;
DECLARE ID_VALUE INT;
DECLARE DATE1_VALUE DATE;
DECLARE Rank1_VALUE INT;
DECLARE DATE2_VALUE DATE;
DECLARE Rank2_VALUE INT;

# testtable is the table that contains data

DECLARE RECORDS_CURSOR CURSOR FOR SELECT *  FROM testtable;

# To check if we reached the end of the result set
DECLARE CONTINUE HANDLER  FOR NOT FOUND SET v_finished = 1;

 # Open cursor
OPEN RECORDS_CURSOR;

# Loop to fetch one row at a time
get_records: LOOP
# Fetch row values to different variables
FETCH RECORDS_CURSOR INTO ID_VALUE, DATE1_VALUE, Rank1_VALUE, DATE2_VALUE, Rank2_VALUE 
# To track the row number
SET ROWNUM = ROWNUM + 1;

# Quit the loop when the end of resultset is reached.
IF v_finished = 1 THEN 
 LEAVE get_records;
 END IF;

# Assign the first row values to the final values. Date2 and Rank2 will be updated when the rank is changed.
IF ROWNUM = 1 THEN
    BEGIN       
        SET ID = ID_VALUE;
        SET DATE1 = DATE1_VALUE;
        SET Rank1 = Rank1_VALUE;
        SET DATE2 = DATE2_VALUE;    
        SET Rank2 = Rank2_VALUE;    
    END;
ELSE 
    BEGIN
        # Date2 and Rank2 is updated with the row values as the rank is changed.
        IF Rank1_VALUE != Rank2_VALUE THEN
            BEGIN
                SET DATE2 =DATE2_VALUE;
                SET Rank2 = Rank2_VALUE;
            END;    
            END IF;
    END;    
END IF;

END LOOP  get_records;

# Select the final values
SELECT ID, DATE1, Rank1, DATE2, Rank2;

# Close cursor
CLOSE RECORDS_CURSOR;

END

创建过程后，您可以按照以下步骤运行此过程

CALL GetChangedRank;

Answer 2

这是你想要的吗？

SELECT * FROM <table name>
WHERE Rank1 <> Rank2

Answer 3

试试这个嵌套查询

Select Id, (select Date1 from TableName group by Rank1) as Date1, Rank1, Date2, Rank2 from TableName where Rank1<>Rank2;