Question

想象一下学生和多位教授一位教授有很多学生学生们在同一时间和日期上课。

表1

ClassName  | ProfessorName |StudentsPresent|ClassStartTime    |ClassDate  |ClassID
Philosophy | Stewart       |10             |8:00              |01/29/2011 | 1
Philosophy | Kyle          |10             |8:00              |01/29/2011 | 1
Religion   | Myke          |11             |8:30              |01/29/2011 | 2
Religion   | Nancy         |11             |8:30              |01/29/2011 | 2

我如何获得以下结果

ClassName  | ProfessorName |StudentsPresent|ClassStartTime    |ClassDate  |ClassID
Philosophy | Stewart,Kyle  |10             |8:00              |01/29/2011 | 1
Religion   | Myke,Nancy    |11             |8:30              |01/29/2011 | 2

正如我们所说，我正在研究游标。

Answer 1

你的桌子似乎非常规范化了。我听说游标在SQL Server中是一个可怕的东西，如果可以的话应该避免。有了它，把它放在一个名为Schedule的表中，这就是我可以满足你的要求的方式。

DECLARE @Schedule TABLE
(
    ClassName VARCHAR(50)
    , ProfessorName VARCHAR(50)
    , StudentsPresent INT
    , ClassStartTime TIME
    , ClassDate DATE
    , ClassID INT
);

INSERT INTO @Schedule
VALUES ('Philosophy', 'Stewart', 10, '8:00', '20110129', 1)
    , ('Philosophy', 'Kyle', 10, '8:00', '20110129', 1)
    , ('Religion', 'Myke', 11, '8:30', '20110129', 2)
    , ('Religion', 'Nancy', 11, '8:30', '20110129', 2);

WITH UniqueClasses AS
(
    SELECT DISTINCT
        ClassName
        , ClassStartTime
        , StudentsPresent
        , ClassDate
        , ClassID
    FROM @Schedule
)
SELECT
    ClassName
    ,   (
            STUFF((
                    SELECT
                        ',' + ProfessorName
                    FROM @Schedule Schedule
                    WHERE Schedule.ClassID = UniqueClasses.ClassID
                    FOR XML PATH('')
                ) , 1, 1, '')
        )AS ProfessorName
    , StudentsPresent
    , StudentsPresent
    ,  ClassStartTime
    , ClassDate
    , ClassID
FROM UniqueClasses

Answer 2

这可能对你有用，但我认为只是在你展示的情况下。

BEGIN
        DECLARE @c CURSOR 
        DECLARE @PrevProfName VARCHAR(250) , @PrevClassDateID INT

        DECLARE @NewTable1 TABLE(
            ClassName           VARCHAR(200),
            ProfessorName       VARCHAR(200),
            StudentsPresent     INT,
            ClassStartTime      DATETIME,
            ClassDateClassID    INT)

        DECLARE 
            @ClassName          VARCHAR(200),
            @ProfessorName      VARCHAR(200),
            @StudentsPresent        INT,
            @ClassStartTime     DATETIME,
            @ClassDateClassID   INT

        OPEN @c SELECT * FROM @NewTable1 ORDER BY ClassDateClassID

        FETCH NEXT FROM @c INTO @ClassName, @ProfessorName, @StudentsPresent, @ClassStartTime, @ClassDateClassID

        WHILE @@FETCH_STATUS = 0
            BEGIN
                IF @PrevProfName <> '' AND @PrevClassDateID > 0
                    BEGIN
                        IF @PrevClassDateID = @ClassDateClassID
                            BEGIN
                                SET @PrevProfName = @PrevProfName + ',' + @ProfessorName
                            END
                        ELSE
                            BEGIN
                                INSERT INTO @NewTable1 VALUES(@ClassName, @PrevProfName, @StudentsPresent, @ClassStartTime, @PrevClassDateID)
                                SET @PrevProfName = @ProfessorName
                                SET @PrevClassDateID = @ClassDateClassID
                            END
                    END
                ELSE
                    BEGIN
                        SET @PrevClassDateID = @ClassDateClassID
                        SET @PrevProfName = @ProfessorName
                    END

                FETCH NEXT FROM @c INTO @ClassName, @ProfessorName, @StudentsPresent, @ClassStartTime, @ClassDateClassID
            END
        CLOSE @c
        DEALLOCATE @c

        SELECT * FROM @NewTable1
    END

SQL将两行或多行合并为一行

2 个答案: