SQL Help: Select statement Concatenate a One to Many relationship

concatenationsqlsql-server

For example I have two tables. The first table is student while the second table are the courses that the a student is taking. How can I use a select statement so that I can see two columns student and courses so that the courses are separated by commas.

Thanks.

Best Solution

Assuming you're using SQL Server 2005:

This should do what you're after - obviously replace fields as you need:

For demo purposes, consider the following two table structures:

Students(
  STU_PKEY Int Identity(1,1) Constraint PK_Students_StuPKey Primary Key,
  STU_NAME nvarchar(64)
)

Courses(
  CRS_PKEY Int Identity(1, 1) Constraint PK_Courses_CrsPKey Primary Key,
  STU_KEY Int Constraint FK_Students_StuPKey Foreign Key References Students(STU_PKEY),
  CRS_NAME nvarchar(64)
)

Now this query should do the job you're after:

Select  s.STU_PKEY, s.STU_NAME As Student,
        Stuff((
            Select  ',' + c.CRS_NAME
            From    Courses c
            Where   s.STU_PKEY = c.STU_KEY
            For     XML Path('')
        ), 1, 1, '') As Courses 
From    Students s
Group By s.STU_PKEY, s.STU_NAME

Way simpler than the currently accepted answer...

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Sql – How to perform an IF…THEN in an SQL SELECT

The CASE statement is the closest to IF in SQL and is supported on all versions of SQL Server.

SELECT CAST(
             CASE
                  WHEN Obsolete = 'N' or InStock = 'Y'
                     THEN 1
                  ELSE 0
             END AS bit) as Saleable, *
FROM Product

You only need to use the CAST operator if you want the result as a Boolean value. If you are happy with an int, this works:

SELECT CASE
            WHEN Obsolete = 'N' or InStock = 'Y'
               THEN 1
               ELSE 0
       END as Saleable, *
FROM Product

CASE statements can be embedded in other CASE statements and even included in aggregates.

SQL Server Denali (SQL Server 2012) adds the IIF statement which is also available in access (pointed out by Martin Smith):

SELECT IIF(Obsolete = 'N' or InStock = 'Y', 1, 0) as Saleable, * FROM Product

Sql-server – Check if table exists in SQL Server

For queries like this it is always best to use an INFORMATION_SCHEMA view. These views are (mostly) standard across many different databases and rarely change from version to version.

To check if a table exists use:

IF (EXISTS (SELECT * 
                 FROM INFORMATION_SCHEMA.TABLES 
                 WHERE TABLE_SCHEMA = 'TheSchema' 
                 AND  TABLE_NAME = 'TheTable'))
BEGIN
    --Do Stuff
END

Best Solution

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Sql – How to perform an IF…THEN in an SQL SELECT

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